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[loopantennas] Re: Remote_Tuned_Loop By Portstevos

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  • mwwong@qbe.com.my
    Howday Mate..... thanks Michael for sharing with us on what you went through.... well, my MVAM108 has yet to arrive from the States and once i ve assemble the
    Message 1 of 12 , Jul 5, 2007
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      Howday Mate.....

      thanks Michael for sharing with us on what you went through....

      well, my MVAM108 has yet to arrive from the States and once i've
      assemble the board, will definately post it in this Group on its
      outcome....

      Alan Wong.




      "portstevos" <portstevos@...>
      Sent by: loopantennas@yahoogroups.com
      07/05/2007 06:40 PM
      Please respond to loopantennas

      To: loopantennas@yahoogroups.com
      cc:
      Subject: [loopantennas] Re: Remote_Tuned_Loop By Portstevos


      --- In loopantennas@yahoogroups.com, "alamdamai1" <mwwong@...> wrote:
      >
      > Hi,
      >
      > I'm currently in the process of purchasing parts for fabricating the
      > loop that Portstevos had posted in the Files Section whereby i would
      > like to seek members further knowledge on the original Kyle KOLR
      > Remote-tuned Loop Pre-amp design....
      >
      > May i enquire is the loop as indicated in Kyle's schematic is
      > referring to the main loop or the smaller coupling loop? (pls refer
      > to filename loopdiagram1 for the schematic....)
      >
      > Reason being i would like to try out Kyle's design of using varactor
      > (tuning) diodes as a tuning capacitor for the main loop...
      >
      > However, if the loop in the schematic is referring to the main loop,
      > then i'm a bit confused at which point in the Pre-amp circuit board
      > do i solder the coupling loop feedline for signal pre-amplification
      > before going out to the receiver?
      >
      > best regards,
      >
      > Alan Wong
      >
      Hello, The Kyle schematic is for the main loop because when using
      varicaps with Kyle's design then there is no coupling loop. I have
      tried various experiments and variations of design such as varicaps
      onto the main loop with and without the pre-amp, I also tried using
      the varicaps to tune the main loop while using a coupling loop with
      and without the pre-amp and I have tried varicaps and pre-amp coming
      from the coupling loop.

      I don't know if I used the incorrect type of varicaps or if there are
      any better types available but I could not get anywhere near the same
      sensitivity and signal to noise ratio, peaking, bandwidth or 'Q' from
      any of the designs using varicaps in comparison to an old fashioned
      tuning gang on the main loop and the pre-amp on the coupling loop, it
      just seem's to be a magic combination for me and has proved to be
      reliable with excellant sensitivity and signal to noise ratio right
      across the frequencies it tunes which is from 2.3 up to 18 MHz (tuning
      to the lower frequencies below 4.7 MHz with the help of a remote
      switching relay to pull in extra capacitance across the main tuning gang!)

      I have also tried an old fashioned tuning gang on the main loop
      without a coupling loop with and without a pre-amp but the best
      performance still comes down to the design that has been posted.

      Best wishes from down under where it is freezing tonight!

      Michael S




      [Non-text portions of this message have been removed]
    • dldorrance
      Hi Alan, Please see inline responses. Dave WA6YSO ... The pre-amp is placed on the main loop. The main loop (inductor) and capacitor (here a varactor setup)
      Message 2 of 12 , Jul 6, 2007
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        Hi Alan,

        Please see inline responses.

        Dave WA6YSO

        --- In loopantennas@yahoogroups.com, "alamdamai1" <mwwong@...> wrote:
        >
        > Hi,
        >
        > I'm currently in the process of purchasing parts for fabricating the
        > loop that Portstevos had posted in the Files Section whereby i would
        > like to seek members further knowledge on the original Kyle KOLR
        > Remote-tuned Loop Pre-amp design....
        >
        > May i enquire is the loop as indicated in Kyle's schematic is
        > referring to the main loop or the smaller coupling loop? (pls refer
        > to filename loopdiagram1 for the schematic....)

        The pre-amp is placed on the main loop. The main loop (inductor) and
        capacitor (here a varactor setup) forms a parallel resonant (tuned)
        circuit. In a small loop, the coupling loop is half of a transformer,
        converting the low impedance of the main loop (well under 1 ohm) up to
        50 ohms, (the standard input for the radio) which achieves maximum
        power transfer.
        >
        > Reason being i would like to try out Kyle's design of using varactor
        > (tuning) diodes as a tuning capacitor for the main loop...
        >
        > However, if the loop in the schematic is referring to the main loop,
        > then i'm a bit confused at which point in the Pre-amp circuit board
        > do i solder the coupling loop feedline for signal pre-amplification
        > before going out to the receiver.

        No tuning loop is needed with the pre-amp. The output of the
        amplifier (the emitter follower) is set for the maximum power
        transfer to the receiver.
        >
        > best regards,
        >
        > Alan Wong
        >
      • Len Warner
        ... Across a tuned loop if it is a high-input-impedance pre-amp (i.e. a JFET-input amplifier); or in series with the loop and its tuning capacitor (if any) for
        Message 3 of 12 , Jul 7, 2007
        • 0 Attachment
          At 12:49 pm ((PDT)) Fri Jul 6, 2007, dldorrance wrote:
          >[snip]
          >The pre-amp is placed on the main loop.

          Across a tuned loop if it is a high-input-impedance pre-amp
          (i.e. a JFET-input amplifier); or in series with the loop and
          its tuning capacitor (if any) for a very-low-impedance pre-amp;
          otherwise use a matching transformation (not necessarily
          a wound transformer).

          >The main loop (inductor) and
          >capacitor (here a varactor setup) forms a parallel resonant (tuned)
          >circuit.

          So it is very high impedance.

          > In a small loop,

          For an electrically small receiving loop, where the length of the
          conductor is typically one-tenth wavelength or less, the loop will
          consist of a single turn or a small number of turns, except at VLF.

          >the coupling loop is half of a transformer,

          With the main loop forming the primary having a few turns or
          one turn; and the coupling loop forming the secondary with one
          turn or one reduced-area turn.

          So it is an impedance step-down ratio transformer.

          >converting the low impedance of the main loop (well under 1 ohm)

          No - you have said it is parallel-resonant so it is high impedance.
          For a series-resonant loop, the impedance is the radiation
          resistance plus the RF resistance of the loop which basically
          depends on how much copper you can afford to put into it.

          >up to

          No - it's definitely a step-down transformer.

          >50 ohms, (the standard input for the radio)

          That depends on the radio (my HF-150 has 50 ohm,
          600 ohm and high-impedance for a whip) and on the
          feeder you use to connect to it - which may be what
          is to hand rather than what you would have chosen..

          Radio coax is commonly 50 ohms but TV coax is 75 ohms.

          Twin feeder is typically 300, 450 or 600-ish ohms.

          Basically, if you want the matching to be independent of
          frequency and feeder length, you match to the characteristic
          impedance of the feeder and, if necessary, match the feeder
          to the radio at the other end.


          Regards, LenW
          --
          From Yahoo! Groups Help: ... trim all the irrelevant quoted text
          out of your message (as a courtesy to the other members of
          the group to make the digest easier to read).
        • mwwong@qbe.com.my
          Hi Dave, please correct me if i m wrong as i m just a beginner in loop antennas.... in summary, if i were to build a remote tuned loop based on Kyle KOLR
          Message 4 of 12 , Jul 8, 2007
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            Hi Dave,

            please correct me if i'm wrong as i'm just a beginner in loop antennas....

            in summary, if i were to build a remote tuned loop based on Kyle KOLR
            design, the tuning & preamp circuit board will be attached to the main
            loop while i still need another smaller coupling loop (ie. as what
            Portstevos
            has illustrated in his phots) as a feedline into my receiver......

            if this is so, do i need another preamp to be connected to the coupling
            loop?

            as alternative, could i just feed into my receiver from the main loop
            without
            the use of any coupling loop similar to the WL1030 design?....

            please forgive if my above queries sounds a bit silly as i'm still
            grasping around
            on antennas designs....

            best regards,

            Alan Wong






            "dldorrance" <dldorrance@...>
            Sent by: loopantennas@yahoogroups.com
            07/07/2007 03:48 AM
            Please respond to loopantennas

            To: loopantennas@yahoogroups.com
            cc:
            Subject: [loopantennas] Re: Remote_Tuned_Loop By Portstevos


            Hi Alan,

            Please see inline responses.

            Dave WA6YSO

            --- In loopantennas@yahoogroups.com, "alamdamai1" <mwwong@...> wrote:
            >
            > Hi,
            >
            > I'm currently in the process of purchasing parts for fabricating the
            > loop that Portstevos had posted in the Files Section whereby i would
            > like to seek members further knowledge on the original Kyle KOLR
            > Remote-tuned Loop Pre-amp design....
            >
            > May i enquire is the loop as indicated in Kyle's schematic is
            > referring to the main loop or the smaller coupling loop? (pls refer
            > to filename loopdiagram1 for the schematic....)

            The pre-amp is placed on the main loop. The main loop (inductor) and
            capacitor (here a varactor setup) forms a parallel resonant (tuned)
            circuit. In a small loop, the coupling loop is half of a transformer,
            converting the low impedance of the main loop (well under 1 ohm) up to
            50 ohms, (the standard input for the radio) which achieves maximum
            power transfer.
            >
            > Reason being i would like to try out Kyle's design of using varactor
            > (tuning) diodes as a tuning capacitor for the main loop...
            >
            > However, if the loop in the schematic is referring to the main loop,
            > then i'm a bit confused at which point in the Pre-amp circuit board
            > do i solder the coupling loop feedline for signal pre-amplification
            > before going out to the receiver.

            No tuning loop is needed with the pre-amp. The output of the
            amplifier (the emitter follower) is set for the maximum power
            transfer to the receiver.
            >
            > best regards,
            >
            > Alan Wong
            >




            [Non-text portions of this message have been removed]
          • dldorrance
            Hi Alan, You are not the only one who is confused. I am at a disadvantage, as I am not able to read the text which accompanies some of his diagrams (too
            Message 5 of 12 , Jul 9, 2007
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              Hi Alan,

              You are not the only one who is confused.

              I am at a disadvantage, as I am not able to read the text which
              accompanies some of his diagrams (too small). However, looking at the
              two amplifier diagrams, the schematic in Preamp2.jpg is to amplify the
              signal coming out of a traditional small loop antenna, which contains
              a main loop tuned with a traditional variable capacitor and a sense
              loop. The preamplifier simply boosts the signal received by the sense
              loop. It is situated between the sense loop and the transmission line
              coax. It has no tuning function.

              The other preamp, see Looppreamp1.jpg, attaches to the main loop in
              place of the variable capacitor (I think). It contains back-to-back
              varactor diodes, which replace the tuning capacitor and can tune the
              main loop by altering the voltage applied to the varactor diodes.
              With this setup no sense loop is needed.

              Most of the amplified remotely tuned small loops I have seen use a
              preamplifier as in looppreamp1.jpg, which is attached to the main loop
              and works without a sense loop.

              So you need to make some choices. First choice is to build a
              traditional small loop with a variable capacitor and a sense loop.
              There are literally hundreds of websites outlining this method. That
              would give you a feel for how small loops work. Second, you could add
              a preamp between the sense loop and the coax. See the diagram in
              Preamp2.jpg. Third you could build a remotely tuned loop with
              varactor diodes attached to a preamplifier (no need for a sense loop)
              see Looppreamp1.jpg.

              That is a rough outline. The details follow from what you want to
              build. I hope this helps (and I hope I got it right).

              Dave



              --- In loopantennas@yahoogroups.com, mwwong@... wrote:
              >
              > Hi Dave,
              >
              > please correct me if i'm wrong as i'm just a beginner in loop
              antennas....
              >
              > in summary, if i were to build a remote tuned loop based on Kyle KOLR
              > design, the tuning & preamp circuit board will be attached to the main
              > loop while i still need another smaller coupling loop (ie. as what
              > Portstevos
              > has illustrated in his phots) as a feedline into my receiver......
              >
              > if this is so, do i need another preamp to be connected to the coupling
              > loop?
              >
              > as alternative, could i just feed into my receiver from the main loop
              > without
              > the use of any coupling loop similar to the WL1030 design?....
              >
              > please forgive if my above queries sounds a bit silly as i'm still
              > grasping around
              > on antennas designs....
              >
              > best regards,
              >
              > Alan Wong
              >
              >
              >
              >
              >
              >
              > "dldorrance" <dldorrance@...>
              > Sent by: loopantennas@yahoogroups.com
              > 07/07/2007 03:48 AM
              > Please respond to loopantennas
              >
              > To: loopantennas@yahoogroups.com
              > cc:
              > Subject: [loopantennas] Re: Remote_Tuned_Loop By
              Portstevos
              >
              >
              > Hi Alan,
              >
              > Please see inline responses.
              >
              > Dave WA6YSO
              >
              > --- In loopantennas@yahoogroups.com, "alamdamai1" <mwwong@> wrote:
              > >
              > > Hi,
              > >
              > > I'm currently in the process of purchasing parts for fabricating the
              > > loop that Portstevos had posted in the Files Section whereby i would
              > > like to seek members further knowledge on the original Kyle KOLR
              > > Remote-tuned Loop Pre-amp design....
              > >
              > > May i enquire is the loop as indicated in Kyle's schematic is
              > > referring to the main loop or the smaller coupling loop? (pls refer
              > > to filename loopdiagram1 for the schematic....)
              >
              > The pre-amp is placed on the main loop. The main loop (inductor) and
              > capacitor (here a varactor setup) forms a parallel resonant (tuned)
              > circuit. In a small loop, the coupling loop is half of a transformer,
              > converting the low impedance of the main loop (well under 1 ohm) up to
              > 50 ohms, (the standard input for the radio) which achieves maximum
              > power transfer.
              > >
              > > Reason being i would like to try out Kyle's design of using varactor
              > > (tuning) diodes as a tuning capacitor for the main loop...
              > >
              > > However, if the loop in the schematic is referring to the main loop,
              > > then i'm a bit confused at which point in the Pre-amp circuit board
              > > do i solder the coupling loop feedline for signal pre-amplification
              > > before going out to the receiver.
              >
              > No tuning loop is needed with the pre-amp. The output of the
              > amplifier (the emitter follower) is set for the maximum power
              > transfer to the receiver.
              > >
              > > best regards,
              > >
              > > Alan Wong
              > >
              >
              >
              >
              >
              > [Non-text portions of this message have been removed]
              >
            • aimo ruoho
              Would this new system be as good or even better than the very costly (excessively expencive) Badbrook antennas? If so, I for 1 would be very much interested to
              Message 6 of 12 , Jul 10, 2007
              • 0 Attachment
                Would this new system be as good or even better than the very costly (excessively expencive) Badbrook antennas?
                If so, I for 1 would be very much interested to build 1 or more of them!
                Aimo

                dldorrance <dldorrance@...> wrote:
                Hi Alan,

                You are not the only one who is confused.

                I am at a disadvantage, as I am not able to read the text which
                accompanies some of his diagrams (too small). However, looking at the
                two amplifier diagrams, the schematic in Preamp2.jpg is to amplify the
                signal coming out of a traditional small loop antenna, which contains
                a main loop tuned with a traditional variable capacitor and a sense
                loop. The preamplifier simply boosts the signal received by the sense
                loop. It is situated between the sense loop and the transmission line
                coax. It has no tuning function.

                The other preamp, see Looppreamp1.jpg, attaches to the main loop in
                place of the variable capacitor (I think). It contains back-to-back
                varactor diodes, which replace the tuning capacitor and can tune the
                main loop by altering the voltage applied to the varactor diodes.
                With this setup no sense loop is needed.

                Most of the amplified remotely tuned small loops I have seen use a
                preamplifier as in looppreamp1.jpg, which is attached to the main loop
                and works without a sense loop.

                So you need to make some choices. First choice is to build a
                traditional small loop with a variable capacitor and a sense loop.
                There are literally hundreds of websites outlining this method. That
                would give you a feel for how small loops work. Second, you could add
                a preamp between the sense loop and the coax. See the diagram in
                Preamp2.jpg. Third you could build a remotely tuned loop with
                varactor diodes attached to a preamplifier (no need for a sense loop)
                see Looppreamp1.jpg.

                That is a rough outline. The details follow from what you want to
                build. I hope this helps (and I hope I got it right).

                Dave

                --- In loopantennas@yahoogroups.com, mwwong@... wrote:
                >
                > Hi Dave,
                >
                > please correct me if i'm wrong as i'm just a beginner in loop
                antennas....
                >
                > in summary, if i were to build a remote tuned loop based on Kyle KOLR
                > design, the tuning & preamp circuit board will be attached to the main
                > loop while i still need another smaller coupling loop (ie. as what
                > Portstevos
                > has illustrated in his phots) as a feedline into my receiver......
                >
                > if this is so, do i need another preamp to be connected to the coupling
                > loop?
                >
                > as alternative, could i just feed into my receiver from the main loop
                > without
                > the use of any coupling loop similar to the WL1030 design?....
                >
                > please forgive if my above queries sounds a bit silly as i'm still
                > grasping around
                > on antennas designs....
                >
                > best regards,
                >
                > Alan Wong
                >
                >
                >
                >
                >
                >
                > "dldorrance" <dldorrance@...>
                > Sent by: loopantennas@yahoogroups.com
                > 07/07/2007 03:48 AM
                > Please respond to loopantennas
                >
                > To: loopantennas@yahoogroups.com
                > cc:
                > Subject: [loopantennas] Re: Remote_Tuned_Loop By
                Portstevos
                >
                >
                > Hi Alan,
                >
                > Please see inline responses.
                >
                > Dave WA6YSO
                >
                > --- In loopantennas@yahoogroups.com, "alamdamai1" <mwwong@> wrote:
                > >
                > > Hi,
                > >
                > > I'm currently in the process of purchasing parts for fabricating the
                > > loop that Portstevos had posted in the Files Section whereby i would
                > > like to seek members further knowledge on the original Kyle KOLR
                > > Remote-tuned Loop Pre-amp design....
                > >
                > > May i enquire is the loop as indicated in Kyle's schematic is
                > > referring to the main loop or the smaller coupling loop? (pls refer
                > > to filename loopdiagram1 for the schematic....)
                >
                > The pre-amp is placed on the main loop. The main loop (inductor) and
                > capacitor (here a varactor setup) forms a parallel resonant (tuned)
                > circuit. In a small loop, the coupling loop is half of a transformer,
                > converting the low impedance of the main loop (well under 1 ohm) up to
                > 50 ohms, (the standard input for the radio) which achieves maximum
                > power transfer.
                > >
                > > Reason being i would like to try out Kyle's design of using varactor
                > > (tuning) diodes as a tuning capacitor for the main loop...
                > >
                > > However, if the loop in the schematic is referring to the main loop,
                > > then i'm a bit confused at which point in the Pre-amp circuit board
                > > do i solder the coupling loop feedline for signal pre-amplification
                > > before going out to the receiver.
                >
                > No tuning loop is needed with the pre-amp. The output of the
                > amplifier (the emitter follower) is set for the maximum power
                > transfer to the receiver.
                > >
                > > best regards,
                > >
                > > Alan Wong
                > >
                >
                >
                >
                >
                > [Non-text portions of this message have been removed]
                >






                ---------------------------------
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                (and love to hate): Yahoo! TV's Guilty Pleasures list.

                [Non-text portions of this message have been removed]
              • jr_dakota
                In the files section there is a file called Loop Circuit.rtf .... The left schematic is what I used, I used a single varactor simply because the signal levels
                Message 7 of 12 , Jul 10, 2007
                • 0 Attachment
                  In the files section there is a file called Loop Circuit.rtf .... The
                  left schematic is what I used, I used a single varactor simply because
                  the signal levels are so small that it's really not necessary to do
                  the series/parallel thing with 4 of them (But you DO need them that
                  way to tune a whip or 'longwire' which will have voltage spikes from
                  noise not present in the magnetic field loop)

                  I don't use that preamp anymore but opted for a lower noise, higher
                  gain, more gain range low impedance RF amp shown in file
                  Lo_Imp_Loop_Preamp

                  The main drawback to my system (well for most people) is that you need
                  to run seperate wires for controlling the tuning, amp gain, and to
                  supply power but IMO this is the best way to go, feeding a coax so the
                  RF has to ride a DC voltage is almost always noisier than seperate
                  feeds for the DC voltages

                  My loop is made from a piece of 1/2" O.D. (Yes O.D. it's refrigeration
                  copper I get for free) soft copper tubing 10 foot long and mounted on
                  my roof with a cheap Channel Master rotor and I use a coax shielded
                  (balanced) pickup loop .... It'll be 3 years in September since I
                  mounted it and other than changing the preamp to the new style, it's
                  never been touched or had a problem ... The preamp has enough gain
                  that I can pickup up a lot of AM BCB stations even though the loop
                  itself only tunes down to ~5 Mhz ...

                  I'm interested to see what my bulletproof RF amplified untuned loop (
                  a Sickbrook clone with MY OWN ORIGINAL CIRCUITRY)) will compare to it

                  JR



                  --- In loopantennas@yahoogroups.com, mwwong@... wrote:
                  >
                  > Howday Mate.....
                  >
                  > thanks Michael for sharing with us on what you went through....
                  >
                  > well, my MVAM108 has yet to arrive from the States and once i've
                  > assemble the board, will definately post it in this Group on its
                  > outcome....
                  >
                  > Alan Wong.
                • jr_dakota
                  The ONLY real advantage a Wellbrook (or any other amplifiied untuned loop) has over a tuned loop is a wide range of operating frequencies and a tuned loop has
                  Message 8 of 12 , Jul 10, 2007
                  • 0 Attachment
                    The ONLY real advantage a Wellbrook (or any other amplifiied untuned
                    loop) has over a tuned loop is a wide range of operating frequencies
                    and a tuned loop has several advantages over an untuned loop as long
                    as you stay in the frequency range the loop is designed for, for
                    instance a tuned loop has some filtering capabilities not present in
                    any untuned loop, it also tends to have a more stable output impedence
                    making the preamp design easier to do effectively or not even having
                    to use a preamp in some cases

                    The down side is to tune from LF up to the upper end of the HF range
                    you need several tuned loops whereas one untuned loop will do the same
                    job **if** you have a well designed wideband RF preamp/impedance
                    converter to go with it

                    I'm working on an untuned amplified loop with a high IP2/IP3 preamp
                    but I don't get much done in the shop during the summer months and I
                    didn't get my antenna analyzer (AmQRP Antenna Analyst "AA-908"),
                    spectrum analyzer (KangaUS kit of Wes Hayward's design) and misc. gear
                    for IP2/IP3 testing done until late spring


                    --- In loopantennas@yahoogroups.com, aimo ruoho <aimounto@...> wrote:
                    >
                    > Would this new system be as good or even better than the very costly
                    (excessively expencive) Badbrook antennas?
                    > If so, I for 1 would be very much interested to build 1 or more of
                    them!
                    > Aimo
                    >
                    > dldorrance <dldorrance@...> wrote:
                    > Hi Alan,
                  • mwwong@qbe.com.my
                    Hi JR, Hmmm.....if i knew earlier the Kyle KOLR design would have a higher noise floor, i would opt for your Pre-amp design which i choose not to earlier as i
                    Message 9 of 12 , Jul 10, 2007
                    • 0 Attachment
                      Hi JR,

                      Hmmm.....if i knew earlier the Kyle KOLR design would have a higher
                      noise floor, i would opt for your Pre-amp design which i choose not to
                      earlier as i thought Kyle's circuit looks more 'sophisticated'.....

                      nevertheless, i will also try out your Pre-amp and see what happens.....

                      oh...great, now i've to order a toroid for the transformer.....

                      best regards,

                      Alan Wong.




                      "jr_dakota" <SG2112@...>
                      Sent by: loopantennas@yahoogroups.com
                      07/11/2007 08:04 AM
                      Please respond to loopantennas

                      To: loopantennas@yahoogroups.com
                      cc:
                      Subject: [loopantennas] Re: Remote_Tuned_Loop By Portstevos


                      In the files section there is a file called Loop Circuit.rtf .... The
                      left schematic is what I used, I used a single varactor simply because
                      the signal levels are so small that it's really not necessary to do
                      the series/parallel thing with 4 of them (But you DO need them that
                      way to tune a whip or 'longwire' which will have voltage spikes from
                      noise not present in the magnetic field loop)

                      I don't use that preamp anymore but opted for a lower noise, higher
                      gain, more gain range low impedance RF amp shown in file
                      Lo_Imp_Loop_Preamp

                      The main drawback to my system (well for most people) is that you need
                      to run seperate wires for controlling the tuning, amp gain, and to
                      supply power but IMO this is the best way to go, feeding a coax so the
                      RF has to ride a DC voltage is almost always noisier than seperate
                      feeds for the DC voltages

                      My loop is made from a piece of 1/2" O.D. (Yes O.D. it's refrigeration
                      copper I get for free) soft copper tubing 10 foot long and mounted on
                      my roof with a cheap Channel Master rotor and I use a coax shielded
                      (balanced) pickup loop .... It'll be 3 years in September since I
                      mounted it and other than changing the preamp to the new style, it's
                      never been touched or had a problem ... The preamp has enough gain
                      that I can pickup up a lot of AM BCB stations even though the loop
                      itself only tunes down to ~5 Mhz ...

                      I'm interested to see what my bulletproof RF amplified untuned loop (
                      a Sickbrook clone with MY OWN ORIGINAL CIRCUITRY)) will compare to it

                      JR

                      --- In loopantennas@yahoogroups.com, mwwong@... wrote:
                      >
                      > Howday Mate.....
                      >
                      > thanks Michael for sharing with us on what you went through....
                      >
                      > well, my MVAM108 has yet to arrive from the States and once i've
                      > assemble the board, will definately post it in this Group on its
                      > outcome....
                      >
                      > Alan Wong.




                      [Non-text portions of this message have been removed]
                    • jr_dakota
                      You ll also need a PIN Diode too (MPN3404 or equiv.) although a 1N4007 will work with just a tad more intermod distortion from what I ve heard .... You can
                      Message 10 of 12 , Jul 11, 2007
                      • 0 Attachment
                        You'll also need a PIN Diode too (MPN3404 or equiv.) although a 1N4007
                        will work with just a tad more intermod distortion from what I've
                        heard .... You can also use a different transistor, a 2N2222 or a
                        2N3904 will work too with a slight (perhaps even imperceptible)
                        increase in Noise Figure

                        You could also set it up with a fixed gain ... If you put the end of
                        C1 to ground and get rid of everything to the left you'd have a fixed
                        gain of about 30db .... you could change the value of R5 to lower the
                        gain or you could remove the grounded end of C1 and put some
                        resistance between it and ground to partially bypass the emitter which
                        is essentially what the PIN diode does ... a 1K ohm Trimmer would
                        probably be the best solution, then you could set it for the gain you
                        want 'by ear' if you don't have the test equipment and then leave it

                        Other than changing the input biasing to 'long tailed biasing' to get
                        the input impedance down to 50 ohms, the rest of the circuit is Wes
                        Hayward's from the book Experimental Methods in RF Design and found in
                        the IF section .... I wanted to be able to control the gain remotely
                        and IF amps are a good place to start for circuits like that ... this
                        particular one doesn't increase in noise when you reduce the gain like
                        most do which made it more adaptable for a front end preamp

                        FETs are great in higher impedance circuits and although you see a lot
                        of 50 ohm FET RF Preamps, I've never been able to get the performance
                        or stabilty I've wanted using them in 50 low impedance circuits ...
                        The previous preamp worked, it was quiet but I never could get enough
                        gain out of it when I needed more than normal, for instance using the
                        antenna outside it's tuning range .... at 50 ohms about all I could
                        get out of it without raising the input impedance was 10-12 db (Which
                        is enough for most antennas but not quite enough for Loops in my
                        experience)

                        JR

                        --- In loopantennas@yahoogroups.com, mwwong@... wrote:
                        >
                        > Hi JR,
                        >
                        > Hmmm.....if i knew earlier the Kyle KOLR design would have a higher
                        > noise floor, i would opt for your Pre-amp design which i choose not to
                        > earlier as i thought Kyle's circuit looks more 'sophisticated'.....
                        >
                        > nevertheless, i will also try out your Pre-amp and see what happens.....
                        >
                        > oh...great, now i've to order a toroid for the transformer.....
                        >
                        > best regards,
                        >
                        > Alan Wong.
                        >
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