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Re:First Loop Experience: Predicted Peformance vs. Actual

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  • Bill McGraw
    I sent two different loop calculators to sernstfortin@yahoo.com plus my difficulties in dealing with any antenna and about my 8 loop that seems to work OK in
    Message 1 of 27 , Jan 6, 2009
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      I sent two different loop calculators to sernstfortin@... plus my
      difficulties in dealing with any antenna and about my 8" loop that seems to
      work OK in the MW band. His narrow frequency range was unusual and makes me
      think to study this some more before making a loop.

      How does one calculate the pf capacitance of a v-cap? I have 9 of them and
      one works well with a crude crystal radio and with 2 inexpensive AM radios
      using the 8" loop. I don't fully understand how to attach the dual v-caps to
      the antenna or loop, sensing coil or without the sensing coil.

      I use my DX 398 to verify frequencies on the AM radios using the 8" loop; I
      have a scanner with an OCF wire taped to my office wall, a square loop
      around my office ceiling for the DX 398 (the regular telescoping antenna
      seems to work as well) and a single loop around a large photo frame that
      seems to work only on FM. All antennas are inside but I had an outside
      aerial at one time.

      "First Loop Experience: Predicted Peformance vs. Actual
      Posted by: "sernstfortin" sernstfortin@... sernstfortin
      Mon Jan 5, 2009 5:08 am (PST)"

      William W."Bill" McGraw
      "Somewhere South of Chicago"
      Greenville, MS 38701
    • C. Beijersbergen
      Others like myself will be interested too, so could you put the article in the Files section? Cor Beijersbergen That is a very nice looking loop John. I use
      Message 2 of 27 , Jan 7, 2009
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        Others like myself will be interested too, so could you put the article in the Files section?

        Cor Beijersbergen


        That is a very nice looking loop John. I use Teflon insulated wire on my
        loops and other antennas. It lasts forever.
        If you can could you send that schematic and article to me? Many thanks.

        Mike
        WE0H



        [Non-text portions of this message have been removed]
      • John Hoopes
        Sam,   One more attachment of the Burhans preamp for you. I will be posting up some more pics in John s Corner of the link coupling I used on the BCB
        Message 3 of 27 , Jan 7, 2009
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          Sam,
           
          One more attachment of the Burhans preamp for you. I will be posting up some more pics in "John's Corner" of the link coupling I used on the BCB antenna later tonight.
           
          John



















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        • John Hoopes
          That s a good idea. I should have done it earlier but didn t think there would be any interest.   John  ... From: C. Beijersbergen
          Message 4 of 27 , Jan 7, 2009
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            That's a good idea. I should have done it earlier but didn't think there would be any interest.
             
            John 

            --- On Wed, 1/7/09, C. Beijersbergen <c.beijersbergen@...> wrote:

            From: C. Beijersbergen <c.beijersbergen@...>
            Subject: Re: [loopantennas] First Loop Experience: Predicted Peformance vs. Actual
            To: loopantennas@yahoogroups.com
            Date: Wednesday, January 7, 2009, 3:05 AM






            Others like myself will be interested too, so could you put the article in the Files section?

            Cor Beijersbergen

            That is a very nice looking loop John. I use Teflon insulated wire on my
            loops and other antennas. It lasts forever.
            If you can could you send that schematic and article to me? Many thanks.

            Mike
            WE0H

            [Non-text portions of this message have been removed]


















            [Non-text portions of this message have been removed]
          • tenorman1952
            ... a ... and ... of ... I ve found Bruce Carter s calculators to be fairly accurate, or at least, in the ballpark. With your figures, 34 x 34 , .19 wire
            Message 5 of 27 , Jan 7, 2009
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              --- In loopantennas@yahoogroups.com, "sernstfortin"
              <sernstfortin@...> wrote:

              > It is composed of 26 turns of 24AWG uninsulated copper wire around
              a
              > square frame made primarily from wood dowels (spent a lot of time
              and
              > effort there). ;)
              >
              > Depth of loop was approx 5inches.
              >
              > Variable air-gap capacitor used was speced by the source that I
              > purchased it from to be 16pF to 390pF.
              >
              > I used the 5/2003 version of Bruce Carter's AM Loop Calculator to
              > predict performance.
              >
              > What I discovered through testing with my radio was a tuning range
              of
              > Freq(lo)= 200KHz, and Freq(hi) = 433KHz...
              >


              I've found Bruce Carter's calculators to be fairly accurate, or at
              least, in the ballpark.

              With your figures, 34" x 34", .19" wire spacing, 26 turns, and your
              tuning cap figures, 16-390 pf, Bruce's calculator shows 165 khz - 815
              khz.

              http://www.mindspring.com/~loop_antenna/umr_emc_calc.htm

              Paul C.
            • Samuel Ernst-Fortin
              I m not an expert, but I know that the construction techniques used could throw a wrench into the predicted. How does one measure the capacitance of a variable
              Message 6 of 27 , Jan 7, 2009
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                I'm not an expert, but I know that the construction techniques used could throw a wrench into the predicted.

                How does one measure the capacitance of a variable cap? Well, one could gen up some form of RC arrangement that is
                either charged or discharged and from the time constant associated with the exponential waveform (oscilloscope or VOM),
                with a known R, you estimate C.

                Or, one could gen up some form of frequency generator (multistable / oscillator) who's freq and period depend on C, and measure
                the frequency or period (oscope most likely, but a frequency meter perhaps) to estimate C, or one could use a suitable Capacitance
                Meter (which ultimately I presume estimates the value of the capacitor under test by one of these methods).

                For all I know, the VOM or oscope may skew the measurement, so I personally may just go out and get a capacitance meter myself.
                They are relatively cheap (you have to make sure you get one that has a resolution of fractional pF if possible).

                If you have a dua-l or tri- or quad-section vcap, I'm thinking you are referring to the number of tunable elements which are essentially
                ganged on the same shaft right? In general, I believe you want to place the sections in parallel to have their individual capacitances sum
                together to give you the widest possible tuning range / span.

                I do not have your vcaps in my hand to look at them, but more than likely, since they share the same shaft, they probably already have
                one leg in common, perhaps the outside shell / frame of the vcap... whatever is in common with the tuning shaft....

                Therefore, to place them all in parallel, you simply tie the stationary portions together electrically (I suspect there would be a solder
                lug for each section). I hope my description is clear.

                OK, now the coils of your loop antenna form the resonant section and the inductance which must be paralleled with the capacitance of your
                vcap to be placed into tunable resonance.

                Your sensing coil: I suspect you either have something wound around the frame (right on top of the resonant windings), or you have
                something smaller forming a loop inside the resonant windings. How many turns? I can't tell you that... like I said I'm a newbee myself.

                If you have a portable shortwave radio, mearly placing your radio inside the resonant coil is enough to provide antenna coupling. No
                sensing coil needed.

                Otherwise, I believe, you have the two wires attached to the antenna plug (you go buy one to fit the radio) wired to the sensing coil.

                Don't ask me what to do if you want to have just some form of aligator clip on with your telescoping antenna.

                I hope others here will help you more as you've about tapped out my working knowledge of loop antennas.

                More reading for me.

                Good luck, and have fun!



                ________________________________
                From: Bill McGraw <mcgr3799@...>
                To: loopantennas@yahoogroups.com
                Sent: Wednesday, January 7, 2009 12:42:08 AM
                Subject: [loopantennas] Re:First Loop Experience: Predicted Peformance vs. Actual


                I sent two different loop calculators to sernstfortin@ yahoo.com plus my
                difficulties in dealing with any antenna and about my 8" loop that seems to
                work OK in the MW band. His narrow frequency range was unusual and makes me
                think to study this some more before making a loop.

                How does one calculate the pf capacitance of a v-cap? I have 9 of them and
                one works well with a crude crystal radio and with 2 inexpensive AM radios
                using the 8" loop. I don't fully understand how to attach the dual v-caps to
                the antenna or loop, sensing coil or without the sensing coil.

                I use my DX 398 to verify frequencies on the AM radios using the 8" loop; I
                have a scanner with an OCF wire taped to my office wall, a square loop
                around my office ceiling for the DX 398 (the regular telescoping antenna
                seems to work as well) and a single loop around a large photo frame that
                seems to work only on FM. All antennas are inside but I had an outside
                aerial at one time.

                "First Loop Experience: Predicted Peformance vs. Actual
                Posted by: "sernstfortin" sernstfortin@ yahoo.com sernstfortin
                Mon Jan 5, 2009 5:08 am (PST)"

                William W."Bill" McGraw
                "Somewhere South of Chicago"
                Greenville, MS 38701






                [Non-text portions of this message have been removed]
              • tenorman1952
                ... could throw a wrench into the predicted. ... could gen up some form of RC arrangement that is ... with the exponential waveform (oscilloscope or VOM), ...
                Message 7 of 27 , Jan 8, 2009
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                  --- In loopantennas@yahoogroups.com, Samuel Ernst-Fortin
                  <sernstfortin@...> wrote:
                  >
                  > I'm not an expert, but I know that the construction techniques used
                  could throw a wrench into the predicted.
                  >
                  > How does one measure the capacitance of a variable cap? Well, one
                  could gen up some form of RC arrangement that is
                  > either charged or discharged and from the time constant associated
                  with the exponential waveform (oscilloscope or VOM),
                  > with a known R, you estimate C.

                  I simply turn the seclector of my digital multimeter to measure
                  capacitance.

                  Paul C.
                • Samuel Ernst-Fortin
                  ... Right, that works. :) In fact, I decided as an early birthday gift to myself, I would purchase one - so this morning I ordered an LCR meter off eBay for a
                  Message 8 of 27 , Jan 8, 2009
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                    Paul writes:
                    >>I simply turn the seclector of my digital multimeter to measure capacitance.

                    Right, that works. :)

                    In fact, I decided as an early birthday gift to myself, I would purchase one - so this morning I ordered an LCR meter off eBay for a reasonable price to complement my VOM.

                    Capacitance from .1pF to 20mF, and inductance from .1uH to 20H.
                    http://www.aidetek.com/New_products_info/Datasheet/Vichy/DM4070.doc

                    I'm aware the accuracy is not that of a more costly high-end meter, but it should be more than sufficient for my purposes.

                    A loop site I like:
                    http://www.mindspring.com/~loop_antenna/
                    Sam
                  • Gary Pewitt
                    Sam, the C and L range you quoted for this model is way off on the lower end of the ranges. I checked it out on e-bay and bought one as the price was quite
                    Message 9 of 27 , Jan 8, 2009
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                      Sam, the C and L range you quoted for this model is way off on the lower
                      end of the ranges. I checked it out on e-bay and bought one as the
                      price was quite good ($50.29 with free shipping. The only ones with the
                      range you quoted cost much more
                      and are probably worth it but more accuracy than I need. thanks for the
                      tip. 73 Gary N9ZSV




                      Samuel Ernst-Fortin wrote:
                      >
                      > Paul writes:
                      > >>I simply turn the seclector of my digital multimeter to measure
                      > capacitance.
                      >
                      > Right, that works. :)
                      >
                      > In fact, I decided as an early birthday gift to myself, I would
                      > purchase one - so this morning I ordered an LCR meter off eBay for a
                      > reasonable price to complement my VOM.
                      >
                      > Capacitance from .1pF to 20mF, and inductance from .1uH to 20H.
                      > http://www.aidetek.com/New_products_info/Datasheet/Vichy/DM4070.doc
                      > <http://www.aidetek.com/New_products_info/Datasheet/Vichy/DM4070.doc>
                      >
                      > I'm aware the accuracy is not that of a more costly high-end meter,
                      > but it should be more than sufficient for my purposes.
                      >
                      > A loop site I like:
                      > http://www.mindspring.com/~loop_antenna/
                      > <http://www.mindspring.com/%7Eloop_antenna/>
                      > Sam
                      >
                      >
                      >
                    • Bill McGraw
                      Thank you Sam as that was clear advice, you answered my questions and I will put your advice to work. I have asked local hams about the cap meter and got
                      Message 10 of 27 , Jan 9, 2009
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                        Thank you Sam as that was clear advice, you answered my questions and I will
                        put your advice to work. I have asked local hams about the cap meter and got
                        insufficient answers from them. From what I can tell you are not a newbie. I
                        am definitely a newbie. I will begin to plan a multi loop antenna that will
                        work for the MW BC band and perhaps higher as well. My inside horizontal
                        loop and outside ground is attached to the stereo plug going into the radio
                        external antenna input, ground to inside and antenna to tip. This subject is
                        taking time away from taking the Technician License test as I have been a
                        frustrated Ham for 50 years due to finding many other interests to pursue.
                        Bill

                        Sam at sernstfortin@... wrote: "so I personally may just go out and
                        get a capacitance meter myself.
                        They are relatively cheap (you have to make sure you get one that has a
                        resolution of fractional pF if possible)."
                        And, "Therefore, to place them all in parallel, you simply tie the
                        stationary portions together electrically (I suspect there would be a solder

                        lug for each section). I hope my description is clear."

                        And, "OK, now the coils of your loop antenna form the resonant section and
                        the inductance which must be paralleled with the capacitance of your
                        vcap to be placed into tunable resonance.

                        Your sensing coil: I suspect you either have something wound around the
                        frame (right on top of the resonant windings), or you have
                        something smaller forming a loop inside the resonant windings. How many
                        turns? I can't tell you that... like I said I'm a newbee myself.

                        If you have a portable shortwave radio, mearly placing your radio inside the
                        resonant coil is enough to provide antenna coupling. No
                        sensing coil needed.

                        Otherwise, I believe, you have the two wires attached to the antenna plug
                        (you go buy one to fit the radio) wired to the sensing coil."


                        William W."Bill" McGraw
                        "Somewhere South of Chicago"
                        Greenville, MS 38701
                      • david
                        hi here is the past few weeks receptions here in scotland using a indoor flag antenna http://uk.youtube.com/profile?user=tvdxrools&view=videos also if anyone
                        Message 11 of 27 , Jan 9, 2009
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                          hi here is the past few weeks receptions here in scotland using a indoor flag antenna http://uk.youtube.com/profile?user=tvdxrools&view=videos also if anyone is interested we have a mw dx chat and cluster running on skype which is getting quite popular if interested search for me on skype tvdxrools many thanks david h scotland

                          [Non-text portions of this message have been removed]
                        • Steve
                          I hook this up to my DMM, the ranges are 200.0pF to 20.00uF full scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V full scale for 20uF.
                          Message 12 of 27 , Jan 9, 2009
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                            I hook this up to my DMM, the ranges are 200.0pF to 20.00uF full
                            scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V
                            full scale for 20uF.

                            <http://www.polyphoto.com/tutorials/Dual555CapMeter/Dual555CapMeter150dpi.jpg>

                            I have a 0.1% tolerance capacitor I keep around to calibrate projects
                            like this.

                            Steve Greenfield

                            > --- In loopantennas@yahoogroups.com, Samuel Ernst-Fortin
                            > <sernstfortin@> wrote:
                            > >
                            > > I'm not an expert, but I know that the construction techniques used
                            > could throw a wrench into the predicted.
                            > >
                            > > How does one measure the capacitance of a variable cap? Well, one
                            > could gen up some form of RC arrangement that is
                            > > either charged or discharged and from the time constant associated
                            > with the exponential waveform (oscilloscope or VOM),
                            > > with a known R, you estimate C.
                          • Samuel Ernst-Fortin
                            Steve, ... I weighed the option of constructing a unit. I like that your design leverages a DVM, That s really slick.;) Where did you get the idea for it? From
                            Message 13 of 27 , Jan 9, 2009
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                              Steve,
                              you wrote:
                              >>I hook this up to my DMM, the ranges are 200.0pF to 20.00uF full
                              >>scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V
                              >>full scale for 20uF.

                              I weighed the option of constructing a unit. I like that your design leverages a DVM, That's really slick.;)
                              Where did you get the idea for it? From just the 555 application notes?
                              Thanks for sharing that.
                              Sam
                            • John Hoopes
                              That s pretty cool Steve. Do you have anything for measuring L? John ... From: Steve Subject: [loopantennas] Re:First Loop Experience:
                              Message 14 of 27 , Jan 12, 2009
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                                That's pretty cool Steve. Do you have anything for measuring L?

                                John

                                --- On Fri, 1/9/09, Steve <alienrelics@...> wrote:
                                From: Steve <alienrelics@...>
                                Subject: [loopantennas] Re:First Loop Experience: Predicted Peformance vs. Actual
                                To: loopantennas@yahoogroups.com
                                Date: Friday, January 9, 2009, 11:57 AM











                                I hook this up to my DMM, the ranges are 200.0pF to 20.00uF full

                                scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V

                                full scale for 20uF.



                                <http://www.polyphot o.com/tutorials/ Dual555CapMeter/ Dual555CapMeter1 50dpi.jpg>



                                I have a 0.1% tolerance capacitor I keep around to calibrate projects

                                like this.



                                Steve Greenfield



                                > --- In loopantennas@ yahoogroups. com, Samuel Ernst-Fortin

                                > <sernstfortin@ > wrote:

                                > >

                                > > I'm not an expert, but I know that the construction techniques used

                                > could throw a wrench into the predicted.

                                > >

                                > > How does one measure the capacitance of a variable cap? Well, one

                                > could gen up some form of RC arrangement that is

                                > > either charged or discharged and from the time constant associated

                                > with the exponential waveform (oscilloscope or VOM),

                                > > with a known R, you estimate C.





























                                [Non-text portions of this message have been removed]
                              • Steve
                                ... leverages a DVM, That s really slick.;) ... I saw a project for one in a magazine long ago that used logic gates. It drifted badly with temp and voltage
                                Message 15 of 27 , Jan 12, 2009
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                                  --- In loopantennas@yahoogroups.com, Samuel Ernst-Fortin
                                  <sernstfortin@...> wrote:
                                  >
                                  > Steve,
                                  > you wrote:
                                  > >>I hook this up to my DMM, the ranges are 200.0pF to 20.00uF full
                                  > >>scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V
                                  > >>full scale for 20uF.
                                  >
                                  > I weighed the option of constructing a unit. I like that your design
                                  leverages a DVM, That's really slick.;)
                                  > Where did you get the idea for it? From just the 555 application notes?
                                  > Thanks for sharing that.

                                  I saw a project for one in a magazine long ago that used logic gates.
                                  It drifted badly with temp and voltage changes and was sensitive to
                                  which revision of gate used. Since the 555 is very stable, I designed
                                  it using a couple 555 gates. It is solid enough, after all my DMM is
                                  only rated at 3% accuracy.

                                  I do have the LCR meter from AADE, too. It works great, although I'm
                                  not that please with the physical design of it. I worry about the
                                  banana jacks getting broken in my toolbox.

                                  Steve Greenfield
                                • Steve
                                  I drew up a design for a double 555 inductance meter, but haven t built one yet. Steve Greenfield ... Peformance vs. Actual ... 20.00uF full ...
                                  Message 16 of 27 , Jan 12, 2009
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                                    I drew up a design for a double 555 inductance meter, but haven't
                                    built one yet.

                                    Steve Greenfield

                                    --- In loopantennas@yahoogroups.com, John Hoopes <jdh1812@...> wrote:
                                    >
                                    > That's pretty cool Steve. Do you have anything for measuring L?
                                    >
                                    > John
                                    >
                                    > --- On Fri, 1/9/09, Steve <alienrelics@...> wrote:
                                    > From: Steve <alienrelics@...>
                                    > Subject: [loopantennas] Re:First Loop Experience: Predicted
                                    Peformance vs. Actual
                                    > To: loopantennas@yahoogroups.com
                                    > Date: Friday, January 9, 2009, 11:57 AM
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    > I hook this up to my DMM, the ranges are 200.0pF to
                                    20.00uF full
                                    >
                                    > scale, using the 200mV scale on the meter for 200pF to 2uF, and 2V
                                    >
                                    > full scale for 20uF.
                                    >
                                    >
                                    >
                                    > <http://www.polyphot o.com/tutorials/ Dual555CapMeter/
                                    Dual555CapMeter1 50dpi.jpg>
                                    >
                                    >
                                    >
                                    > I have a 0.1% tolerance capacitor I keep around to calibrate projects
                                    >
                                    > like this.
                                    >
                                    >
                                    >
                                    > Steve Greenfield
                                    >
                                    >
                                    >
                                    > > --- In loopantennas@ yahoogroups. com, Samuel Ernst-Fortin
                                    >
                                    > > <sernstfortin@ > wrote:
                                    >
                                    > > >
                                    >
                                    > > > I'm not an expert, but I know that the construction techniques used
                                    >
                                    > > could throw a wrench into the predicted.
                                    >
                                    > > >
                                    >
                                    > > > How does one measure the capacitance of a variable cap? Well, one
                                    >
                                    > > could gen up some form of RC arrangement that is
                                    >
                                    > > > either charged or discharged and from the time constant associated
                                    >
                                    > > with the exponential waveform (oscilloscope or VOM),
                                    >
                                    > > > with a known R, you estimate C.
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    >
                                    > [Non-text portions of this message have been removed]
                                    >
                                  • Samuel Ernst-Fortin
                                    ... I like and appreciate very much the large LCD display. Yes, the banana jacks seem a little marginal, but you can pull them out and attach the measured cap
                                    Message 17 of 27 , Jan 12, 2009
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                                      Steve, you wrote:
                                      >>
                                      >>I do have the LCR meter from AADE, too. It works great, although I'm
                                      >>not that please with the physical design of it. I worry about the
                                      >>banana jacks getting broken in my toolbox.

                                      I like and appreciate very much the large LCD display. Yes, the banana jacks
                                      seem a little marginal, but you can pull them out and attach the measured
                                      cap or inductor to the metal clips. This isn't practical with a var cap nor the
                                      windings, specially if the gauge of the wire is small.

                                      But, for a $40, i'm not complaining. When I started adding everything up for
                                      making one, and putting it in a case, etc, powering it, paying for shipping of
                                      parts, the purchase off eBay made absolute sense.
                                      Sam
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