Loading ...
Sorry, an error occurred while loading the content.

Loop Antenna for WWVB LF Receiver

Expand Messages
  • redsp
    Hi, I m making an all digital WWVB receiver with a goal of having the lowest power consumption possible. I am using an FPGA designed for very low power
    Message 1 of 27 , Jan 6, 2013
    • 0 Attachment
      Hi,

      I'm making an all digital WWVB receiver with a goal of having the lowest power consumption possible. I am using an FPGA designed for very low power dissipation which has differential inputs I can use in a poor man's Delta Sigma ADC. I believe I can make it pretty sensitive with high processing gain to pull the signal out of the noise. Being on the east coast that will be important.

      To minimize the power consumption I want to eliminate the RF amp. I have done a lot of research on the antenna and I think the shielded loop will give the largest signal without an amp.

      After reading a number of web pages on loop antennas, a *very* large number of web pages, I decided to use a 2 foot diameter loop with 8 turns of RG-6 cable (solid copper core) as a reasonable compromise between ease of construction, size and effectiveness. This is 50 feet and I might add another 50 feet so I can use it without hacking the shield in the middle of the cable. I estimate a 2 foot loop with 50 foot of coax will give me a signal of approximately 30 uV from a 100 uV/m signal. To couple the antenna and receiver I am planning to use a ferrite loop with a number of turns of magnet wire as a transformer giving an even higher output voltage of 1 to 3 mV depending on how many turns I can get on the loop.

      Any suggestions or thoughts?

      Rick
    • John Popelish
      On 01/06/2013 08:08 PM, redsp wrote: (snip) ... I suggest you use a pair of ferrite beads, side by side, as the core for the output matching transformer. Any
      Message 2 of 27 , Jan 10, 2013
      • 0 Attachment
        On 01/06/2013 08:08 PM, redsp wrote:
        (snip)
        > To couple the antenna and receiver I am planning to use a
        > ferrite loop with a number of turns of magnet wire as a
        > transformer giving an even higher output voltage of 1 to
        > 3 mV depending on how many turns I can get on the loop.
        >
        > Any suggestions or thoughts?

        I suggest you use a pair of ferrite beads, side by side, as
        the core for the output matching transformer. Any low
        frequency ferrite shield bead. I think the next better form
        is a single high permeability ferrite toroid.

        It will be smaller, lower loss and not pick up any other
        signals from the environment that get added to the received
        signal.

        --
        Regards,

        John Popelish
      • redsp
        ... Hi John, Which do you mean by it , the torroid? Rick
        Message 3 of 27 , Jan 12, 2013
        • 0 Attachment
          --- In loopantennas@yahoogroups.com, John Popelish wrote:
          >
          > On 01/06/2013 08:08 PM, redsp wrote:
          > (snip)
          > > To couple the antenna and receiver I am planning to use a
          > > ferrite loop with a number of turns of magnet wire as a
          > > transformer giving an even higher output voltage of 1 to
          > > 3 mV depending on how many turns I can get on the loop.
          > >
          > > Any suggestions or thoughts?
          >
          > I suggest you use a pair of ferrite beads, side by side, as
          > the core for the output matching transformer. Any low
          > frequency ferrite shield bead. I think the next better form
          > is a single high permeability ferrite toroid.
          >
          > It will be smaller, lower loss and not pick up any other
          > signals from the environment that get added to the received
          > signal.

          Hi John,

          Which do you mean by "it", the torroid?

          Rick
        • John Popelish
          ... I mean either of these closed magnetic path transformers will be smaller, lower loss and not pick up any other signal, compared to a rod form (open
          Message 4 of 27 , Jan 12, 2013
          • 0 Attachment
            On 01/12/2013 01:59 PM, redsp wrote:
            > --- In loopantennas@yahoogroups.com, John Popelish wrote:


            >> I suggest you use a pair of ferrite beads, side by side, as
            >> the core for the output matching transformer. Any low
            >> frequency ferrite shield bead. I think the next better form
            >> is a single high permeability ferrite toroid.
            >>
            >> It will be smaller, lower loss and not pick up any other
            >> signals from the environment that get added to the received
            >> signal.
            >
            > Hi John,
            >
            > Which do you mean by "it", the torroid?

            I mean either of these closed magnetic path transformers
            will be smaller, lower loss and not pick up any other
            signal, compared to a rod form (open magnetic path) of
            transformer.

            --
            Regards,

            John Popelish
          • redsp
            ... Ok, thanks. I ll probably go with the single toroid because I want to get 100 turns or so on the secondary to give me a larger output signal. Might be a
            Message 5 of 27 , Jan 13, 2013
            • 0 Attachment
              --- In loopantennas@yahoogroups.com, John Popelish wrote:
              >
              > On 01/12/2013 01:59 PM, redsp wrote:
              > > --- In loopantennas@yahoogroups.com, John Popelish wrote:
              >
              > >> I suggest you use a pair of ferrite beads, side by side, as
              > >> the core for the output matching transformer. Any low
              > >> frequency ferrite shield bead. I think the next better form
              > >> is a single high permeability ferrite toroid.
              > >>
              > >> It will be smaller, lower loss and not pick up any other
              > >> signals from the environment that get added to the received
              > >> signal.
              > >
              > > Hi John,
              > >
              > > Which do you mean by "it", the toroid?
              >
              > I mean either of these closed magnetic path transformers
              > will be smaller, lower loss and not pick up any other
              > signal, compared to a rod form (open magnetic path) of
              > transformer.

              Ok, thanks. I'll probably go with the single toroid because I want to get 100 turns or so on the secondary to give me a larger output signal. Might be a little harder with two cores. What mu number would be "high"?

              I'll likely get one from a broken PC power supply... if I can find a broken PC power supply. All the PCs I've scrounged from the trash lately have been working when I hooked them up, so I'm still looking.

              One of the many loop antenna pages I visited, and the only one that used a core for coupling, used a toroid from an old PC power supply. He had a ton of them and used a bunch of the voltage switches for a power of 2 cap bank to tune the antenna. Very nicely done.

              Rick
            • John Popelish
              ... Any ferrite that has a measurable resistance when touched with the points of ohm meter leads will probably have usefully high permeability at 60 kHz. If
              Message 6 of 27 , Jan 13, 2013
              • 0 Attachment
                On 01/13/2013 10:32 AM, redsp wrote:

                > Ok, thanks. I'll probably go with the single toroid
                > because I want to get 100 turns or so on the secondary to
                > give me a larger output signal. Might be a little harder
                > with two cores. What mu number would be "high"?

                Any ferrite that has a measurable resistance when touched
                with the points of ohm meter leads will probably have
                usefully high permeability at 60 kHz. If you have several
                cores to choose from, lower resistance generally indicates
                higher permeability. The stuff made for megahertz signals
                almost always shows an unmeasurably high resistance.

                > I'll likely get one from a broken PC power supply... if I
                > can find a broken PC power supply. All the PCs I've
                > scrounged from the trash lately have been working when I
                > hooked them up, so I'm still looking.

                Yes, power ferrites are pretty good transformer material for
                60 kHz signal use. But many of these are not ferrite, but
                powdered iron, low permeability, energy storage cores.
                Those are almost always painted with bright colors, as a
                material code. Some ferrite is also painted for insulation
                purposes, but not usually. You can nick the paint with a
                file for the resistance test. Ferrite is also black and
                glassy hard, while the powdered iron material is usually
                light grey and soft enough to nick with a file.

                > One of the many loop antenna pages I visited, and the
                > only one that used a core for coupling, used a toroid
                > from an old PC power supply. He had a ton of them and
                > used a bunch of the voltage switches for a power of 2 cap
                > bank to tune the antenna. Very nicely done.

                Cup cores (pot cores) and other two piece transformer types
                are very handy for comparative experiments, because the coil
                is wound on a bobbin (that can be swapped out). You just
                have to find core pairs that do not have a gap between the
                center pegs (which lowers the effective permeability).

                I have a pretty good collection of such things, so if you
                contact me by email, I may be able to send you a little kit
                of parts to play with.

                --
                Regards,

                John Popelish
              • redsp
                ... Sounds like useful info. This is stuff I should know about, but have never worked with. ... More important info. ... Actually, after I sent my last reply
                Message 7 of 27 , Jan 13, 2013
                • 0 Attachment
                  --- In loopantennas@yahoogroups.com, John Popelish wrote:
                  >
                  > On 01/13/2013 10:32 AM, redsp wrote:
                  >
                  > > Ok, thanks. I'll probably go with the single toroid
                  > > because I want to get 100 turns or so on the secondary to
                  > > give me a larger output signal. Might be a little harder
                  > > with two cores. What mu number would be "high"?
                  >
                  > Any ferrite that has a measurable resistance when touched
                  > with the points of ohm meter leads will probably have
                  > usefully high permeability at 60 kHz. If you have several
                  > cores to choose from, lower resistance generally indicates
                  > higher permeability. The stuff made for megahertz signals
                  > almost always shows an unmeasurably high resistance.

                  Sounds like useful info. This is stuff I should know about, but have never worked with.


                  > > I'll likely get one from a broken PC power supply... if I
                  > > can find a broken PC power supply. All the PCs I've
                  > > scrounged from the trash lately have been working when I
                  > > hooked them up, so I'm still looking.
                  >
                  > Yes, power ferrites are pretty good transformer material for
                  > 60 kHz signal use. But many of these are not ferrite, but
                  > powdered iron, low permeability, energy storage cores.
                  > Those are almost always painted with bright colors, as a
                  > material code. Some ferrite is also painted for insulation
                  > purposes, but not usually. You can nick the paint with a
                  > file for the resistance test. Ferrite is also black and
                  > glassy hard, while the powdered iron material is usually
                  > light grey and soft enough to nick with a file.

                  More important info.


                  > > One of the many loop antenna pages I visited, and the
                  > > only one that used a core for coupling, used a toroid
                  > > from an old PC power supply. He had a ton of them and
                  > > used a bunch of the voltage switches for a power of 2 cap
                  > > bank to tune the antenna. Very nicely done.
                  >
                  > Cup cores (pot cores) and other two piece transformer types
                  > are very handy for comparative experiments, because the coil
                  > is wound on a bobbin (that can be swapped out). You just
                  > have to find core pairs that do not have a gap between the
                  > center pegs (which lowers the effective permeability).
                  >
                  > I have a pretty good collection of such things, so if you
                  > contact me by email, I may be able to send you a little kit
                  > of parts to play with.

                  Actually, after I sent my last reply I was doing a search for a toroid core and found an interesting video on toroidal core winding. I couldn't quite see how the machine worked in the video, so I'll watch it again full screen to see if I can pick up some details.

                  While watching the video, I realized that this is pretty much the same as a current transformer. After doing a search on Digikey I found a number of secondary coils that should do the job. But then magnetics are not my strong suit. Certainly it is a lot easier to buy one of these for $3 plus shipping than winding my own core. Do you think this would be a useful transformer for a 60 kHz antenna?

                  http://www.digikey.com/product-detail/en/PE-51688NL/553-1546-ND/2265978

                  Or should I find a good core and wind it myself? My goal is to get the highest output voltage so I think I just need to use as many windings on the coil as practical. It will be driving a very high impedance input, not a coax.

                  Rick
                • John Popelish
                  ... When I wind toroid cores, I find a wooden dowel much smaller than the hole in the core, usually a foot or a little more, long. I notch both ends and wind
                  Message 8 of 27 , Jan 13, 2013
                  • 0 Attachment
                    On 01/13/2013 12:45 PM, redsp wrote:

                    > Actually, after I sent my last reply I was doing a
                    > search for a toroid core and found an interesting video
                    > on toroidal core winding. I couldn't quite see how the
                    > machine worked in the video, so I'll watch it again full
                    > screen to see if I can pick up some details.

                    When I wind toroid cores, I find a wooden dowel much smaller
                    than the hole in the core, usually a foot or a little more,
                    long. I notch both ends and wind the wire between these
                    notches, to make a supply of wire I can easily pass through
                    the core. This long bobbin makes it a lot easier to pass a
                    supply of wire, multiple times through the hole in a toroid.

                    > While watching the video, I realized that this is pretty
                    > much the same as a current transformer.

                    Exactly the same.

                    > After doing a search on Digikey I found a number of
                    > secondary coils that should do the job. But then
                    > magnetics are not my strong suit. Certainly it is a lot
                    > easier to buy one of these for $3 plus shipping than
                    > winding my own core. Do you think this would be a useful
                    > transformer for a 60 kHz antenna?

                    Most current transformers are made with metallic ribbon
                    cores that are optimized for line frequencies, though some
                    are made of ferrite for switching power supply CT
                    applications. The ferrite ones might well serve for the
                    secondary of a 60kHz transformer.

                    > http://www.digikey.com/product-detail/en/PE-51688NL/553-1546-ND/2265978

                    That one is certainly made for your frequency range.

                    > Or should I find a good core and wind it myself? My
                    > goal is to get the highest output voltage so I think I
                    > just need to use as many windings on the coil as
                    > practical. It will be driving a very high impedance
                    > input, not a coax.

                    I think that CT might be a good place to start some
                    experiments. But keep in mind that your pickup coil is not
                    a zero ohm voltage source, but has some impedance. That
                    impedance will limit how high you can jack up the voltage
                    with a transformer, before the transformer starts to load
                    down the voltage from the coil. But you might push it a bit
                    higher by resonating both the coil and transformer with
                    capacitors (reduce their usable bandwidth, but peak the
                    response around the desired frequency).

                    Do you have an oscilloscope or other means to measure the
                    signal you are working with? I made a field generating
                    coil, to produce a stronger drive signal than WWVB, for such
                    experiments, so I had enough signal to make accurate,
                    comparative measurements.

                    --
                    Regards,

                    John Popelish
                  • redsp
                    ... Thanks for the tip. ... Looking at the shape I realize these transformers may just be coils rather than toroids. Will that make a difference? ... Yes, I
                    Message 9 of 27 , Jan 14, 2013
                    • 0 Attachment
                      --- In loopantennas@yahoogroups.com, John Popelish wrote:
                      >
                      > When I wind toroid cores, I find a wooden dowel much smaller
                      > than the hole in the core, usually a foot or a little more,
                      > long. I notch both ends and wind the wire between these
                      > notches, to make a supply of wire I can easily pass through
                      > the core. This long bobbin makes it a lot easier to pass a
                      > supply of wire, multiple times through the hole in a toroid.

                      Thanks for the tip.


                      > Most current transformers are made with metallic ribbon
                      > cores that are optimized for line frequencies, though some
                      > are made of ferrite for switching power supply CT
                      > applications. The ferrite ones might well serve for the
                      > secondary of a 60kHz transformer.

                      Looking at the shape I realize these transformers may just be coils rather than toroids. Will that make a difference?


                      > > http://www.digikey.com/product-detail/en/PE-51688NL/553-1546-ND/2265978
                      >
                      > That one is certainly made for your frequency range.
                      >
                      > I think that CT might be a good place to start some
                      > experiments. But keep in mind that your pickup coil is not
                      > a zero ohm voltage source, but has some impedance. That
                      > impedance will limit how high you can jack up the voltage
                      > with a transformer, before the transformer starts to load
                      > down the voltage from the coil. But you might push it a bit
                      > higher by resonating both the coil and transformer with
                      > capacitors (reduce their usable bandwidth, but peak the
                      > response around the desired frequency).
                      >
                      > Do you have an oscilloscope or other means to measure the
                      > signal you are working with? I made a field generating
                      > coil, to produce a stronger drive signal than WWVB, for such
                      > experiments, so I had enough signal to make accurate,
                      > comparative measurements.

                      Yes, I have an oscope and a signal generator that can make a 60 kHz sine wave. I will be testing the antenna shortly. There are a lot of facets to this project and I tend to bounce around between them rather than work solely on one part at a time.

                      The load (receiver input) will be very high impedance (megohms), so I can't imagine a 10 ohm coil resistance will matter much. I will look into tuning the transformer output as well as the antenna coil. Thanks.

                      Rick
                    • John Popelish
                      ... No, I think the one you linked to, below, has a high permeability, ferrite, toroid core. Without a core, it would have an extremely low output. (snip) ...
                      Message 10 of 27 , Jan 14, 2013
                      • 0 Attachment
                        On 01/14/2013 11:59 AM, redsp wrote:
                        >
                        >
                        > --- In loopantennas@yahoogroups.com, John Popelish
                        > wrote:

                        > Looking at the shape I realize these transformers may
                        > just be coils rather than toroids. Will that make a
                        > difference?

                        No, I think the one you linked to, below, has a high
                        permeability, ferrite, toroid core. Without a core, it
                        would have an extremely low output.

                        (snip)
                        >> Do you have an oscilloscope or other means to measure
                        >> the signal you are working with? I made a field
                        >> generating coil, to produce a stronger drive signal
                        >> than WWVB, for such experiments, so I had enough signal
                        >> to make accurate, comparative measurements.
                        >
                        > Yes, I have an oscope and a signal generator that can
                        > make a 60 kHz sine wave. I will be testing the antenna
                        > shortly. There are a lot of facets to this project and I
                        > tend to bounce around between them rather than work
                        > solely on one part at a time.
                        >
                        > The load (receiver input) will be very high impedance
                        > (megohms), so I can't imagine a 10 ohm coil resistance
                        > will matter much. I will look into tuning the
                        > transformer output as well as the antenna coil. Thanks.

                        It ,may be megohms at DC, but there is also stray
                        capacitance across that 200 turn secondary (most of it,
                        inside the CT, itself. If you use a single turn primary to
                        get the full 200X voltage multiplication, that capacitance
                        looks 200^2=40,000 times larger, across that one turn
                        primary. So several primary turns may be a more optimal
                        load for the loop. Experiment will tell, especially if you
                        sweep frequencies near 60kHz. You may be able to peak the
                        response almost just by selecting the right number of
                        primary turns, leaving only a little need for additional
                        resonating capacitor.

                        --
                        Regards,

                        John Popelish
                      • John Popelish
                        On 01/14/2013 11:59 AM, redsp wrote: (snip) ... Don t forget that that 1:200 transformer will also reflect a 1 megohm amplifier input impedance down to 25 ohms
                        Message 11 of 27 , Jan 14, 2013
                        • 0 Attachment
                          On 01/14/2013 11:59 AM, redsp wrote:
                          (snip)
                          > The load (receiver input) will be very high impedance
                          > (megohms), so I can't imagine a 10 ohm coil resistance
                          > will matter much. I will look into tuning the
                          > transformer output as well as the antenna coil.

                          Don't forget that that 1:200 transformer will also reflect a
                          1 megohm amplifier input impedance down to 25 ohms across
                          the primary.

                          --
                          Regards,

                          John Popelish
                        • redsp
                          ... Are you sure the reflected image of the resistance and capacitance will be proportional to the coil ratio squared and not just the coil ratio? I see I
                          Message 12 of 27 , Jan 14, 2013
                          • 0 Attachment
                            --- In loopantennas@yahoogroups.com, John Popelish wrote:
                            >
                            > On 01/14/2013 11:59 AM, redsp wrote:
                            > (snip)
                            > > The load (receiver input) will be very high impedance
                            > > (megohms), so I can't imagine a 10 ohm coil resistance
                            > > will matter much. I will look into tuning the
                            > > transformer output as well as the antenna coil.
                            >
                            > Don't forget that that 1:200 transformer will also reflect a
                            > 1 megohm amplifier input impedance down to 25 ohms across
                            > the primary.

                            Are you sure the reflected image of the resistance and capacitance will be proportional to the coil ratio squared and not just the coil ratio? I see I need to dig into this a bit more.

                            Rick
                          • John Popelish
                            ... Quite. Voltage changes by turns ratio and current by inverse turns ratio. But impedance is the ratio of voltage divided by current, so the turns ratio
                            Message 13 of 27 , Jan 14, 2013
                            • 0 Attachment
                              On 01/14/2013 12:51 PM, redsp wrote:

                              > Are you sure the reflected image of the resistance and
                              > capacitance will be proportional to the coil ratio
                              > squared and not just the coil ratio? I see I need to dig
                              > into this a bit more.

                              Quite.

                              Voltage changes by turns ratio and current by inverse turns
                              ratio. But impedance is the ratio of voltage divided by
                              current, so the turns ratio comes into the impedance ratio,
                              twice (second power).

                              --
                              Regards,

                              John Popelish
                            • redsp
                              ... You ve given me something to think about. What about the inductance of the secondary? How does that impact the primary circuit? Wouldn t that affect the
                              Message 14 of 27 , Jan 16, 2013
                              • 0 Attachment
                                --- In loopantennas@yahoogroups.com, John Popelish wrote:
                                >
                                > On 01/14/2013 12:51 PM, redsp wrote:
                                >
                                > > Are you sure the reflected image of the resistance and
                                > > capacitance will be proportional to the coil ratio
                                > > squared and not just the coil ratio? I see I need to dig
                                > > into this a bit more.
                                >
                                > Quite.
                                >
                                > Voltage changes by turns ratio and current by inverse turns
                                > ratio. But impedance is the ratio of voltage divided by
                                > current, so the turns ratio comes into the impedance ratio,
                                > twice (second power).

                                You've given me something to think about. What about the inductance of the secondary? How does that impact the primary circuit? Wouldn't that affect the tuning of the primary?

                                I fired up my scope today and found it is not working properly. The horizontal sweep seems to be a bit diminished. So I may be in the market for a new one. I also have an equally old HP signal generator which seems to be outputting what looks like a rectified sine wave on the scale that covers 60 kHz. The lower ranges look fine. I took the cover off (for the first time) and it has a bazillion discretes and a number of transistors. Not sure where to start fixing it. Maybe I need a new sig gen as well. :(

                                Rick
                              • jpopelish
                                ... (snip) According to the data sheet, the 200 turn winding has at least 80mH inductance. That means a single turn primary will have only 1/40,000th of that
                                Message 15 of 27 , Jan 16, 2013
                                • 0 Attachment
                                  --- In loopantennas@yahoogroups.com, "redsp" wrote:

                                  > You've given me something to think about. What about the inductance of the secondary? How does that impact the primary circuit? Wouldn't that affect the tuning of the primary?
                                  (snip)

                                  According to the data sheet, the 200 turn winding has at least 80mH inductance. That means a single turn primary will have only 1/40,000th of that or 2uH inductance. This gives you an idea of the core they used, since you know roughly the size, and that it produces about 2uHy with one turn.

                                  But you can add as many turns as you wish to the primary to raise the primary inductance and lower the turns ratio.

                                  You can also tune the inductance with capacitance. This might work best with a series capacitor between the loop and the primary, and a parallel capacitance across the secondary of the transformer.

                                  Sorry to hear about your test equipment.

                                  --
                                  Regards,

                                  John Popelish
                                • jpopelish
                                  ... (snip) The core is probably something like Fair-rite part# 5975000301. http://www.fair-rite.com/cgibin/catalog.pgm#select:onepart It produces at least 2.16
                                  Message 16 of 27 , Jan 16, 2013
                                  • 0 Attachment
                                    --- In loopantennas@yahoogroups.com, "jpopelish" wrote:

                                    > According to the data sheet, the 200 turn winding has at least 80mH inductance. That means a single turn primary will have only 1/40,000th of that or 2uH inductance. This gives you an idea of the core they used, since you know roughly the size, and that it produces about 2uHy with one turn.
                                    (snip)

                                    The core is probably something like Fair-rite part# 5975000301.
                                    http://www.fair-rite.com/cgibin/catalog.pgm#select:onepart
                                    It produces at least 2.16 uH with one turn.

                                    --

                                    Regards,

                                    John Popelish
                                  • redsp
                                    ... I ve been doing some LTspice simulations on this. I think I need to add some passive circuitry to apply a DC bias to put the differential input on the
                                    Message 17 of 27 , Feb 24, 2013
                                    • 0 Attachment
                                      --- In loopantennas@yahoogroups.com, "jpopelish" <jpopelish@...> wrote:
                                      >
                                      > --- In loopantennas@yahoogroups.com, "redsp" wrote:
                                      >
                                      > > You've given me something to think about. What about the inductance of the secondary? How does that impact the primary circuit? Wouldn't that affect the tuning of the primary?
                                      > (snip)
                                      >
                                      > According to the data sheet, the 200 turn winding has at least 80mH inductance. That means a single turn primary will have only 1/40,000th of that or 2uH inductance. This gives you an idea of the core they used, since you know roughly the size, and that it produces about 2uHy with one turn.
                                      >
                                      > But you can add as many turns as you wish to the primary to raise the primary inductance and lower the turns ratio.
                                      >
                                      > You can also tune the inductance with capacitance. This might work best with a series capacitor between the loop and the primary, and a parallel capacitance across the secondary of the transformer.

                                      I've been doing some LTspice simulations on this. I think I need to add some passive circuitry to apply a DC bias to put the differential input on the edge of triggering, so I included this in the simulation along with the parasitic capacitance of the chip input. The antenna has a loop inductance of about 90 uH. In LTspice the transformer turns ratio is indicated by attaching the corresponding inductance on the secondary (L1*N^2). I'm not sure how a real transformer works in this regard, inductance of primary and secondary.

                                      At very high turns ratios the parasitic capacitance creates a resonance with a null when looking at the tuning capacitance on the antenna. If that gets too close in frequency to the peak for the signal, it greatly disrupts the Q and the bandwidth making it very twitchy to tuning. Using the secondary capacitance alone to tune the response seems to drop the output voltage significantly with readings of -dB rather than some +60 to +70 dB when tuned with the primary capacitor. I'm not familiar with analysis of this circuit to understand why a null is created on the primary cap, but not the output...

                                      The optimum balance seems to be a turns ratio around 25 to 33. In this range the difference in tuned output is in the 1 dB ballpark, but if the secondary capacitance drifts 1 pF the offtuning creates anywhere from -4 to -6 dB attenuation. Oddly at the higher turns ratios where the tuned signal is strongest the attenuation is such that the offtuned signal is weaker than at lower turns ratios. I'm not sure how realistic is a 1 pF drift with temperature, etc. of the inductor, PCB traces and the IC input.

                                      Even odder is that if I add some capacitance to the secondary side in an attempt to swamp out the parasitic capacitance, the circuit has a higher Q and becomes *more* sensitive to that same 1 pF change!!!

                                      I think I am a bit concerned with the capacitance of the secondary coil. If it has much capacitance I will have to run the coil with an even lower turns ratio.

                                      No wonder they call it *complex* math.

                                      Rick
                                    • John Popelish
                                      On 02/24/2013 05:30 PM, redsp wrote: (snip) ... (snip) If you upload your simulation file (not raw file), I will take a look and check out your simulation, as
                                      Message 18 of 27 , Feb 24, 2013
                                      • 0 Attachment
                                        On 02/24/2013 05:30 PM, redsp wrote:

                                        (snip)
                                        > At very high turns ratios the parasitic capacitance
                                        > creates a resonance with a null when looking at the
                                        > tuning capacitance on the antenna. If that gets too
                                        > close in frequency to the peak for the signal, it greatly
                                        > disrupts the Q and the bandwidth making it very twitchy
                                        > to tuning. Using the secondary capacitance alone to tune
                                        > the response seems to drop the output voltage
                                        > significantly with readings of -dB rather than some +60
                                        > to +70 dB when tuned with the primary capacitor. I'm not
                                        > familiar with analysis of this circuit to understand why
                                        > a null is created on the primary cap, but not the
                                        > output...
                                        >
                                        > The optimum balance seems to be a turns ratio around 25
                                        > to 33. In this range the difference in tuned output is
                                        > in the 1 dB ballpark, but if the secondary capacitance
                                        > drifts 1 pF the offtuning creates anywhere from -4 to -6
                                        > dB attenuation. Oddly at the higher turns ratios where
                                        > the tuned signal is strongest the attenuation is such
                                        > that the offtuned signal is weaker than at lower turns
                                        > ratios. I'm not sure how realistic is a 1 pF drift with
                                        > temperature, etc. of the inductor, PCB traces and the IC
                                        > input.
                                        >
                                        > Even odder is that if I add some capacitance to the
                                        > secondary side in an attempt to swamp out the parasitic
                                        > capacitance, the circuit has a higher Q and becomes
                                        > *more* sensitive to that same 1 pF change!!!
                                        >
                                        > I think I am a bit concerned with the capacitance of the
                                        > secondary coil. If it has much capacitance I will have
                                        > to run the coil with an even lower turns ratio.
                                        (snip)

                                        If you upload your simulation file (not raw file), I will
                                        take a look and check out your simulation, as best I can.

                                        Maybe I'll be able to suggest some improvement.

                                        --
                                        Regards,

                                        John Popelish
                                      • redsp
                                        ... I uploaded the simulation files to Antenna_LTspice.zip One is just the basic antenna circuit with the parasitic capacitance on the IC inputs. The other
                                        Message 19 of 27 , Feb 26, 2013
                                        • 0 Attachment
                                          --- In loopantennas@yahoogroups.com, John Popelish <jpopelish@...> wrote:
                                          >
                                          > If you upload your simulation file (not raw file), I will
                                          > take a look and check out your simulation, as best I can.
                                          >
                                          > Maybe I'll be able to suggest some improvement.


                                          I uploaded the simulation files to Antenna_LTspice.zip One is just the basic antenna circuit with the parasitic capacitance on the IC inputs. The other includes some circuitry I am adding to make the digital input work for low level AC signals.

                                          I've done some more work with the simulation and I've also been doing some reading on tuned circuit and I think I understand it better. I can calculate the frequency of the various artifacts that I see now. To calculate the resonance peak, I need to reflect the secondary side capacitance to the primary side using the square of the turns ratio. Adding this to the primary capacitance and using that with the primary inductance gives me the frequency of resonance. The null in the primary cap (C1) voltage is just the resonance of the secondary side. When the frequency is reached where the parasitic cap (C2) resonates without the primary cap, the result is that the voltage on the L1 side of the transformer matches the exciting voltage and the C1 capacitor sees no voltage, so a null.

                                          This is really a red herring and I was just confused by it. When this null gets close to the primary resonance, it means the secondary cap is getting very large and the primary cap is getting small. In the limit of using no primary cap the secondary cap will create a resonance but it won't have the advantage of the transformer turns ratio I expect and the resulting peak is not nearly as high as it could be. This limits the turns ratio to around 75 before the circuit becomes self resonant with the secondary parasitic capacitance.

                                          I was seeing higher Q factors when I used a little secondary capacitance. But this doesn't really improve the signal strength at the output a lot. My real circuit has some passives to provide DC biasing so the digital input on the receiver will be most sensitive to the antenna signal. I included these components in the simulation file antenna.asc while antenna_transformer.asc only includes the transformer. These components were made high impedance, but still have some affect on the Q and max signal strength, limiting it to around 70 dB in the simulation.

                                          In the end the best way to operate this circuit is with a turns ratio around 25 to 33 and with a minimum of capacitance on the secondary. This still produces a decent gain without the response being excessively peaky and overly sensitive to small changes in the secondary capacitance.

                                          The coils I ended up with have 300 turns so I will be wrapping some number of turns on the primary to adjust the turns ratio. So that I can experiment with this, I expect to have multiple coils for the primary, 1, 2, 4 and 8 which will let me combine them in 15 combinations to produce turns ratios between 20 and 300.

                                          My main concern is just how much variation I will see from temperature effects on the circuit once it has been tuned for 60,000 Hz. It may be very twitchy depending on how sensitive the parasitic capacitance is to temperature.

                                          BTW, I've learned a lot about LTspice doing this design, not to mention tuned transformer circuits.

                                          Rick
                                        • John Popelish
                                          ... I took a look at your tuned transformer circuit and have altered it to illustrate a few concepts. I changed out the voltage source in the primary loop
                                          Message 20 of 27 , Feb 26, 2013
                                          • 0 Attachment
                                            On 02/26/2013 07:15 PM, redsp wrote:

                                            > I uploaded the simulation files to Antenna_LTspice.zip
                                            > One is just the basic antenna circuit with the parasitic
                                            > capacitance on the IC inputs. The other includes some
                                            > circuitry I am adding to make the digital input work for
                                            > low level AC signals.

                                            I took a look at your tuned transformer circuit and have
                                            altered it to illustrate a few concepts. I changed out the
                                            voltage source in the primary loop with a current fed, field
                                            coil, as a signal source. I also added an inductor in the
                                            primary loop to represent the antenna coil. The field coil
                                            is very loosely coupled to the antenna coil (K = 0.001), to
                                            represent the magnetic field the antenna will pick up from
                                            space, without the field generator coil having any
                                            significant effect on the tuning of the antenna inductor.

                                            I also rearranged the current transformer, so that the
                                            secondary is a fixed inductance (as a prefab CT will have)
                                            and made the primary inductance a function of the primary
                                            turns count (that you will add).

                                            I am working with a very clunky Windows simulator in a Linux
                                            system, so I did not have time to clean up everything and
                                            make sure all your measure commands still made sense. But I
                                            hope the concepts I introduced are clear enough to be useful
                                            for you.

                                            I uploaded the file to the Popelish folder as
                                            Antenna_transformer_w_loop.asc

                                            If I get the chance, I may work on it a bit more.

                                            Let me know if this makes any sense to you.

                                            --
                                            Regards,

                                            John Popelish
                                          • redsp
                                            ... I have wondered about the way I apply the stimulus. I think you misunderstand the circuit. L1 is the antenna coil. This is a large loop of wire which
                                            Message 21 of 27 , Feb 26, 2013
                                            • 0 Attachment
                                              --- In loopantennas@yahoogroups.com, John Popelish <jpopelish@...> wrote:
                                              >
                                              > On 02/26/2013 07:15 PM, redsp wrote:
                                              >
                                              > > I uploaded the simulation files to Antenna_LTspice.zip
                                              > > One is just the basic antenna circuit with the parasitic
                                              > > capacitance on the IC inputs. The other includes some
                                              > > circuitry I am adding to make the digital input work for
                                              > > low level AC signals.
                                              >
                                              > I took a look at your tuned transformer circuit and have
                                              > altered it to illustrate a few concepts. I changed out the
                                              > voltage source in the primary loop with a current fed, field
                                              > coil, as a signal source. I also added an inductor in the
                                              > primary loop to represent the antenna coil. The field coil
                                              > is very loosely coupled to the antenna coil (K = 0.001), to
                                              > represent the magnetic field the antenna will pick up from
                                              > space, without the field generator coil having any
                                              > significant effect on the tuning of the antenna inductor.
                                              >
                                              > I also rearranged the current transformer, so that the
                                              > secondary is a fixed inductance (as a prefab CT will have)
                                              > and made the primary inductance a function of the primary
                                              > turns count (that you will add).

                                              I have wondered about the way I apply the stimulus. I think you misunderstand the circuit. L1 is the antenna coil. This is a large loop of wire which will make N turns around the coil core. I am unclear if the stimulus signal should be in series with the primary loop or if it should be applied across the cap and coil. In one case the primary will be a series resonant circuit in the other a parallel resonant circuit. The manner of stimulus is the only distinction that I can see between the two.

                                              I'm not sure why the transformer should be changed the way you did. The antenna loop (L1) has a defined inductance. I actually had to research pretty hard to find a decent formula for it. Turns out there are *many* inductance formula and it is not so easy to figure out which one applies. How does the inductance of the two coils interact? I haven't found any good info on this. Most references assume both coils are wound in a similar way on a common core. I suppose the N turns around the core will affect the inductance of the primary. I don't have a number for the inductance of the secondary, the data sheet gives a very wide range, 180 - 335mH @1V, 10kHz.


                                              > I am working with a very clunky Windows simulator in a Linux
                                              > system, so I did not have time to clean up everything and
                                              > make sure all your measure commands still made sense. But I
                                              > hope the concepts I introduced are clear enough to be useful
                                              > for you.
                                              >
                                              > I uploaded the file to the Popelish folder as
                                              > Antenna_transformer_w_loop.asc
                                              >
                                              > If I get the chance, I may work on it a bit more.
                                              >
                                              > Let me know if this makes any sense to you.

                                              I appreciate the time you are spending on this. One thing that still doesn't work perfectly is the center frequency measurement. It finds the max output value ok, but finding the frequency of that max value is not so easy. The method I use sometimes seems to "skip" over the match to the max value and gives an error. No information in the error message of course. LTspice is pretty great, but ease of use is not at the top of the list. BTW, they say LTspice runs great under wine. Have you tried that?

                                              Rick
                                            • redsp
                                              Just after I sent the prior message I was looking at the schematic and I get what you are doing with the separate coils in the primary. One is the antenna
                                              Message 22 of 27 , Feb 26, 2013
                                              • 0 Attachment
                                                Just after I sent the prior message I was looking at the schematic and I get what you are doing with the separate coils in the primary. One is the antenna loop itself and the other is the turns around the secondary coil core. That makes sense. I'll play with this new configuration a bit.

                                                Thanks,

                                                Rick
                                              • John Popelish
                                                ... There are probably several equivalent ways to put energy into the antenna, but I like the field coil approach, because I actually made a field coil to
                                                Message 23 of 27 , Feb 26, 2013
                                                • 0 Attachment
                                                  On 02/26/2013 09:40 PM, redsp wrote:

                                                  > I have wondered about the way I apply the stimulus. I
                                                  > think you misunderstand the circuit. L1 is the antenna
                                                  > coil. This is a large loop of wire which will make N
                                                  > turns around the coil core. I am unclear if the stimulus
                                                  > signal should be in series with the primary loop or if it
                                                  > should be applied across the cap and coil. In one case
                                                  > the primary will be a series resonant circuit in the
                                                  > other a parallel resonant circuit. The manner of
                                                  > stimulus is the only distinction that I can see between
                                                  > the two.

                                                  There are probably several equivalent ways to put energy
                                                  into the antenna, but I like the field coil approach,
                                                  because I actually made a field coil to stimulate antennas.

                                                  The problem with your schematic is that the antenna coil
                                                  inductance is a separate inductive component than the
                                                  transformer primary, because one receives energy from the
                                                  external field and the other does not.

                                                  > I'm not sure why the transformer should be changed the
                                                  > way you did. The antenna loop (L1) has a defined
                                                  > inductance. I actually had to research pretty hard to
                                                  > find a decent formula for it. Turns out there are *many*
                                                  > inductance formula and it is not so easy to figure out
                                                  > which one applies. How does the inductance of the two
                                                  > coils interact? I haven't found any good info on this.
                                                  > Most references assume both coils are wound in a similar
                                                  > way on a common core. I suppose the N turns around the
                                                  > core will affect the inductance of the primary. I don't
                                                  > have a number for the inductance of the secondary, the
                                                  > data sheet gives a very wide range, 180 - 335mH @1V,
                                                  > 10kHz.

                                                  And the secondary inductance is not very high Q (it includes
                                                  significant core loss that shows up as something like a
                                                  parallel resistance across the secondary, because the high
                                                  permeability core is quite conductive). That is why the
                                                  entire system should not be tuned at the output of the
                                                  transformer. You don't want all the resonant stored energy
                                                  to have to slosh back and forth through that core. Most of
                                                  the inductive energy should be stored only in the high Q
                                                  antenna coil.

                                                  >> I am working with a very clunky Windows simulator in a
                                                  >> Linux system, so I did not have time to clean up
                                                  >> everything and make sure all your measure commands
                                                  >> still made sense.

                                                  (snip)

                                                  > BTW, they say LTspice runs great under wine. Have
                                                  > you tried that?

                                                  I tried, once, to install Wine, and hit a roadblock. My son
                                                  is the Linux expert in the family, and one of these days, I
                                                  want to try again, with his help.

                                                  --
                                                  Regards,

                                                  John Popelish
                                                • jpopelish
                                                  One other point. There are two completely complementary ways to use a coupling transformer, in an attempt to increase the signal output of your loop. The
                                                  Message 24 of 27 , Feb 27, 2013
                                                  • 0 Attachment
                                                    One other point. There are two completely complementary ways to use a coupling transformer, in an attempt to increase the signal output of your loop. The transformer primary can be in series with both the loop and the tuning capacitor, when the primary inductance is low (relative to the loop inductance), or in parallel with both the loop inductor and tuning capacitor, when the primary inductance is high (relative to the loop inductance). If the turns ratio is not large, you might also find a small improvement by putting the secondary in series with the primary (correctly phased to have their voltages add), since you do not need electrical isolation from the transformer, That way, both windings contribute to the output voltage.

                                                    In your simulations, I think you should compare the possibilities for both these approaches with connecting your amplifier input directly across the parallel combination of loop and tuning capacitor.

                                                    One of the three might be a clear winner.

                                                    --
                                                    Regards,

                                                    John Popelish
                                                  • redsp
                                                    ... ll And the secondary inductance is not very high Q (it includes ... But is this core loss included in the simulation? I don t see a term for that
                                                    Message 25 of 27 , Feb 27, 2013
                                                    • 0 Attachment
                                                      --- In loopantennas@yahoogroups.com, John Popelish <jpopelish@...> wrote:
                                                      >
                                                      > On 02/26/2013 09:40 PM, redsp wrote:
                                                      >
                                                      ll> And the secondary inductance is not very high Q (it includes
                                                      > significant core loss that shows up as something like a
                                                      > parallel resistance across the secondary, because the high
                                                      > permeability core is quite conductive). That is why the
                                                      > entire system should not be tuned at the output of the
                                                      > transformer. You don't want all the resonant stored energy
                                                      > to have to slosh back and forth through that core. Most of
                                                      > the inductive energy should be stored only in the high Q
                                                      > antenna coil.

                                                      But is this core loss included in the simulation? I don't see a term for that anywhere.

                                                      Actually I get a higher Q by adding some capacitance to the secondary which increases the secondary currrent, but requires a lowering of the primary capacitance. I assume this is because the reduced primary current raises the Q of the primary circuit. So in the simulation I think the Q of the secondary is higher than the Q of the primary.


                                                      > >> I am working with a very clunky Windows simulator in a
                                                      > >> Linux system, so I did not have time to clean up
                                                      > >> everything and make sure all your measure commands
                                                      > >> still made sense.
                                                      >
                                                      > (snip)
                                                      >
                                                      > > BTW, they say LTspice runs great under wine. Have
                                                      > > you tried that?
                                                      >
                                                      > I tried, once, to install Wine, and hit a roadblock. My son
                                                      > is the Linux expert in the family, and one of these days, I
                                                      > want to try again, with his help.

                                                      Some folks use a dual boot arrangement. Others run one OS and then run another in a sandbox under the first. I expect this takes a pretty good machine with lots of memory. Not something I have.

                                                      I worked on the measurement scripts a bit today. I am trying to measure all three features I see. I can calculate the frequency of the Vcap null exactly. That is the resonance of secondary inductance and capacitance. I can get within 5% of the first peak which is due to the total capacitance and the sum of the two inductors in the primary. But it is always low. I can't come up with any explanation of the higher frequency peak. No combination of inductance and capacitance in the circuit seems to produce this. I'm not comfortable not understanding what the simulation is telling me. That is rather the idea I think, to see what it does and make sure it fits with the model. Otherwise the model may not be right. Obviously I don't understand the model.

                                                      I don't fully understand the field coil circuit. Why did you pick 1 mH for the radiator L4? I have no idea how to include that into the calculations and I don't know if this changes the signal strength value, not that it necessarily is a meaningful number anyway. But in my original circuit I assume the generator is the "untuned" voltage the antenna would receive and so the signal strength at Vout would be a realistic estimate of the level at the receiver input. I will try the other two methods of stimulating the circuit.

                                                      I also have some trouble getting LTspice to display "measured" data in meaningful ways. If it displays some data in dB, then *all* data is measured in dB. So if you want to see a straight numbmer it has to be reversed to anti-dB before being displayed. That is what some of my measurement statements were doing. lol

                                                      If you are interested I've uploaded a new file to your directory. Antenna_trans_LTspice.zip This contains the schematic with the radiator inductance set to match the antenna coil inductance along with the measurement file that can be run from the menu, File - Execute MEAS. Script. It is also in the schematic as commands, but the measure script can be run subsequent to the simulation.

                                                      I'm learning a few things about LTspice, but I still find the .MEAS command to be very cryptic.

                                                      Rick
                                                    • John Popelish
                                                      ... If you put a resistor across the secondary, you have a rough approximation of it. I think something in the decade of 1meg is close. You might also add a
                                                      Message 26 of 27 , Feb 27, 2013
                                                      • 0 Attachment
                                                        On 02/27/2013 06:11 PM, redsp wrote:
                                                        > jpopelish@...> wrote:
                                                        >>... includes
                                                        >> significant core loss that shows up as something like
                                                        >> a parallel resistance across the secondary, because the
                                                        >> high permeability core is quite conductive). That is
                                                        >> why the entire system should not be tuned at the output
                                                        >> of the transformer. You don't want all the resonant
                                                        >> stored energy to have to slosh back and forth through
                                                        >> that core. Most of the inductive energy should be
                                                        >> stored only in the high Q antenna coil.
                                                        >
                                                        > But is this core loss included in the simulation? I
                                                        > don't see a term for that anywhere.

                                                        If you put a resistor across the secondary, you have a rough
                                                        approximation of it. I think something in the decade of
                                                        1meg is close. You might also add a series resistance to
                                                        that 300 turn secondary, since it is wound of pretty fine
                                                        wire. Something about two times the specified DC resistance
                                                        (to account for skin effect) might be about right. Of
                                                        course, you can use the alternate Chan model of a core and
                                                        get a lot closer for the distortion across the waveform, but
                                                        that adds little to an AC analysis.

                                                        > Actually I get a higher Q by adding some capacitance to
                                                        > the secondary which increases the secondary currrent, but
                                                        > requires a lowering of the primary capacitance. I assume
                                                        > this is because the reduced primary current raises the Q
                                                        > of the primary circuit. So in the simulation I think the
                                                        > Q of the secondary is higher than the Q of the primary.

                                                        This is especially true if the transformer primary is
                                                        connected in parallel to the loop and tuning capacitor
                                                        (voltage transformer, rather than current transformer),
                                                        since resonating the transformer will raise its overall
                                                        impedance at the signal frequency.

                                                        (snip)
                                                        > Some folks use a dual boot arrangement. Others run one
                                                        > OS and then run another in a sandbox under the first. I
                                                        > expect this takes a pretty good machine with lots of
                                                        > memory. Not something I have.

                                                        I have a pretty spiffy machine. So I think it will handle
                                                        Wine okay, once I get it installed, correctly.

                                                        > I worked on the measurement scripts a bit today. I am
                                                        > trying to measure all three features I see. I can
                                                        > calculate the frequency of the Vcap null exactly. That
                                                        > is the resonance of secondary inductance and capacitance.
                                                        > I can get within 5% of the first peak which is due to the
                                                        > total capacitance and the sum of the two inductors in the
                                                        > primary. But it is always low. I can't come up with any
                                                        > explanation of the higher frequency peak. No combination
                                                        > of inductance and capacitance in the circuit seems to
                                                        > produce this. I'm not comfortable not understanding what
                                                        > the simulation is telling me. That is rather the idea I
                                                        > think, to see what it does and make sure it fits with the
                                                        > model. Otherwise the model may not be right. Obviously
                                                        > I don't understand the model.

                                                        I am not sure I am following you, here. We may have to get
                                                        together via email and work on the sane schematic, at the
                                                        same time.
                                                        >
                                                        > I don't fully understand the field coil circuit. Why did
                                                        > you pick 1 mH for the radiator L4? I have no idea how to
                                                        > include that into the calculations and I don't know if
                                                        > this changes the signal strength value, not that it
                                                        > necessarily is a meaningful number anyway. But in my
                                                        > original circuit I assume the generator is the "untuned"
                                                        > voltage the antenna would receive and so the signal
                                                        > strength at Vout would be a realistic estimate of the
                                                        > level at the receiver input. I will try the other two
                                                        > methods of stimulating the circuit.

                                                        The field coil inductance and driving current source are
                                                        completely arbitrary. They both function only as a signal
                                                        scale. It would probably be a good idea to pick a field
                                                        coil inductance and current so that a plain loop inductance,
                                                        possibly terminated with a meg ohm resistor or some such,
                                                        produced a 0db output at 60kHz. Then all other signal
                                                        strengths would be equivalent to gains.

                                                        > I also have some trouble getting LTspice to display
                                                        > "measured" data in meaningful ways. If it displays some
                                                        > data in dB, then *all* data is measured in dB. So if you
                                                        > want to see a straight numbmer it has to be reversed to
                                                        > anti-dB before being displayed. That is what some of my
                                                        > measurement statements were doing. lol
                                                        >
                                                        > If you are interested I've uploaded a new file to your
                                                        > directory. Antenna_trans_LTspice.zip This contains the
                                                        > schematic with the radiator inductance set to match the
                                                        > antenna coil inductance along with the measurement file
                                                        > that can be run from the menu, File - Execute MEAS.
                                                        > Script. It is also in the schematic as commands, but the
                                                        > measure script can be run subsequent to the simulation.
                                                        >
                                                        > I'm learning a few things about LTspice, but I still find
                                                        > the .MEAS command to be very cryptic.

                                                        I'll take a look. I have more problems with measure
                                                        commands than all other features of LTspice, put together.

                                                        I'm hoping for an expanded help section on this feature,
                                                        eventually.

                                                        --
                                                        Regards,

                                                        John Popelish
                                                      • jpopelish
                                                        ... (snip) ... I added a second loop inductor to the schematic, loaded only with 1meg and also coupled to both the field coil and the antenna coil by the same
                                                        Message 27 of 27 , Feb 27, 2013
                                                        • 0 Attachment
                                                          <jpopelish@...> wrote:
                                                          > redsp wrote:
                                                          (snip)
                                                          > > I don't fully understand the field coil circuit. Why did
                                                          > > you pick 1 mH for the radiator L4? I have no idea how to
                                                          > > include that into the calculations and I don't know if
                                                          > > this changes the signal strength value, not that it
                                                          > > necessarily is a meaningful number anyway. But in my
                                                          > > original circuit I assume the generator is the "untuned"
                                                          > > voltage the antenna would receive and so the signal
                                                          > > strength at Vout would be a realistic estimate of the
                                                          > > level at the receiver input. I will try the other two
                                                          > > methods of stimulating the circuit.
                                                          >
                                                          > The field coil inductance and driving current source are
                                                          > completely arbitrary. They both function only as a signal
                                                          > scale. It would probably be a good idea to pick a field
                                                          > coil inductance and current so that a plain loop inductance,
                                                          > possibly terminated with a meg ohm resistor or some such,
                                                          > produced a 0db output at 60kHz. Then all other signal
                                                          > strengths would be equivalent to gains.

                                                          I added a second loop inductor to the schematic, loaded only with 1meg and also coupled to both the field coil and the antenna coil by the same 0.001 K factor, and it looks like a field coil inductance of about 80mHy produces a 0db signal across that calibration inductor at 60 kHz. It also shows about a +-0.2 db signal swing as the antenna circuit passes through resonance, so this gives you an idea of how approximate the field coil is at representing a far field. Perhaps it would be a bit better to lower the K factor to 0.0001 and raise the field coil inductance to 800mHy. (a 0.02db coupling of the antenna back into the field coil.)

                                                          --
                                                          Regards,

                                                          John Popelish
                                                        Your message has been successfully submitted and would be delivered to recipients shortly.