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Re: Regen Antenna Isolation

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  • n1tev
    Hi Bill (and the group), I ve come up with a very simple and useful RF amplifier for both solid state and tube regens. I ve been meaning to write this up and
    Message 1 of 8 , Dec 1, 2005
      Hi Bill (and the group),
      I've come up with a very simple and useful RF amplifier for both
      solid state and tube regens. I've been meaning to write this up and
      (hopefully) publish the circuit in QST magazine.

      With regens, it's VERY important to use an RF stage that's simple,
      stable, and broadband. If you try to add a tuned RF stage it's
      extremely difficult to get the thing to "track" the hi Q (Q
      multiplied) LC circuits in a regen, so it's better to use an untuned
      circuit.

      Here's my RF stage. This simple add-on circuit will completely
      eliminate the hand capacitance detuning effect found on the QST
      simple regen. It's a grounded base RF amp with a fair amount of
      gain and isolation. This was designed for use with the
      QST "Beginner's regen" circuit but should work well with any regen
      needing an RF stage for antenna isolation.

      Use a 2N2222 transistor. From emitter through a 1k resistor to
      ground. Also from emitter through something big (like a 0.01
      microFarad) cap to whip antenna. If external antenna is used run
      through about 5PF to antenna from emitter. Base is 0.01 microFarad
      cap to ground and also from base directly to +9V. From collector
      through ANY RFC around 1 millihenry: you can drop in a lot of RFCs
      into this with no real change as RF stage is driving the VERY hi Z
      tank of a regen circuit. Then from collector again through a 5pF cap
      to the top of the coil in the regen (also the tuning cap with the
      simple regen). Now...a 5pF value is OK for the QST beginner's regen
      but with other sets, this value should be changed to get the best
      performance. You can use two tightly twisted wires as a coupling
      cap or substitute cap values as you prefer. With the set running
      increase cap value until set detunes or otherwise does not go
      cleanly into oscillation. Couple-in as much signal as you can
      WITHOUT increasing the detuning: the regen oscillation point should
      still be "sharp" (no "fuzz" in sound at threshold).

      If you are coupling into an input winding or something other than a
      Hi-Z LC tank you may need 50pF or so..just experiment.

      For a tube regen, just run the 6.3V filament voltage through a 100
      Ohm resistor to a 100 MicroFarad (or greater) filter cap. This will
      give you about +9V to power the circuit.

      If you operate the RF amplifier on voltages other than +9V you will
      (probably) want to change the emitter resistor value. The emitter
      voltage is +9V minus the base/emitter junction voltage with is
      around 0.7V. So, with +8.3 volts on the emitter, emitter current
      (using a 1k resistor) will be 8.3 volts divided by 1k with equals
      8.3mA. You don't want to go much below 5mA as the RF stage will
      then be subject to AM detection (strong AM band stations will cause
      the transistor's emitter/base junction to AM detect..with then over
      rides the shortwave you are trying to receive). I've seen a lot of
      published RF stages with use traps to try to prevent this but much
      simpler just to run RF stage current high enough to prevent this.
      So..bottom line: just take desired supply voltage minus 0.7V and
      divide 8mA into it to find new value for emitter resistor. Easy.

      73 DE N1TEV





      --- In regenrx@yahoogroups.com, "Bill Jones" <kd7s@p...> wrote:
      >
      > Hello Friends,
      >
      > I have been having a ball with Charles Kitchin's "A Simple Regen
      Radio for
      > Beginners" from the September, 2000, issue of QST. I set my
      version up to
      > tune the 31 meter band which also gets WWV and the 30 meter ham
      band.
      >
      > I want to build another one but I'd like to add a simple r.f.
      amplifier.
      > I'm not interested in the additional gain as much as I am
      isolating the
      > antenna from the main tank circuit. Instead of using a
      telescoping whip as
      > suggested in the original article I substituted a 36" piece of
      wire. It
      > works well but as the wire moves or the length changes, so does
      the
      > frequency response of the radio.
      >
      > Has anyone "been there, done that?"
      > ========================
      > Bill Jones KD7S <><
      > http://www.psnw.com/~kd7s
      > Sanger, California
      > ========================
      >
    • Bill Jones
      Many thanks, Charles, for suggesting an r.f. amp for the Sept. 2000, QST regen. From your description I have drawn a schematic and posted it on my web site.
      Message 2 of 8 , Dec 1, 2005
        Many thanks, Charles, for suggesting an r.f. amp for the Sept. 2000, QST
        regen. From your description I have drawn a schematic and posted it on my
        web site. As time permits, would you please click on the link below to make
        sure I followed your description correctly. If it is drawn correctly I will
        upload it to the files area of this group. Again, thank you for your help
        and generosity.

        http://www.psnw.com/~kd7s/RegenRFamp.jpg
        ========================
        Bill Jones KD7S <><
        http://www.psnw.com/~kd7s
        Sanger, California
        ========================
        ----- Original Message -----
        From: "n1tev" <n1tev@...>
        To: <regenrx@yahoogroups.com>
        Sent: Thursday, December 01, 2005 9:39 AM
        Subject: [regenrx] Re: Regen Antenna Isolation


        > Hi Bill (and the group),
        > I've come up with a very simple and useful RF amplifier for both
        > solid state and tube regens. I've been meaning to write this up and
        > (hopefully) publish the circuit in QST magazine.
        >
        > With regens, it's VERY important to use an RF stage that's simple,
        > stable, and broadband. If you try to add a tuned RF stage it's
        > extremely difficult to get the thing to "track" the hi Q (Q
        > multiplied) LC circuits in a regen, so it's better to use an untuned
        > circuit.
        >
        > Here's my RF stage. This simple add-on circuit will completely
        > eliminate the hand capacitance detuning effect found on the QST
        > simple regen. It's a grounded base RF amp with a fair amount of
        > gain and isolation. This was designed for use with the
        > QST "Beginner's regen" circuit but should work well with any regen
        > needing an RF stage for antenna isolation.
        >
        > Use a 2N2222 transistor. From emitter through a 1k resistor to
        > ground. Also from emitter through something big (like a 0.01
        > microFarad) cap to whip antenna. If external antenna is used run
        > through about 5PF to antenna from emitter. Base is 0.01 microFarad
        > cap to ground and also from base directly to +9V. From collector
        > through ANY RFC around 1 millihenry: you can drop in a lot of RFCs
        > into this with no real change as RF stage is driving the VERY hi Z
        > tank of a regen circuit. Then from collector again through a 5pF cap
        > to the top of the coil in the regen (also the tuning cap with the
        > simple regen). Now...a 5pF value is OK for the QST beginner's regen
        > but with other sets, this value should be changed to get the best
        > performance. You can use two tightly twisted wires as a coupling
        > cap or substitute cap values as you prefer. With the set running
        > increase cap value until set detunes or otherwise does not go
        > cleanly into oscillation. Couple-in as much signal as you can
        > WITHOUT increasing the detuning: the regen oscillation point should
        > still be "sharp" (no "fuzz" in sound at threshold).
        >
        > If you are coupling into an input winding or something other than a
        > Hi-Z LC tank you may need 50pF or so..just experiment.
        >
        > For a tube regen, just run the 6.3V filament voltage through a 100
        > Ohm resistor to a 100 MicroFarad (or greater) filter cap. This will
        > give you about +9V to power the circuit.
        >
        > If you operate the RF amplifier on voltages other than +9V you will
        > (probably) want to change the emitter resistor value. The emitter
        > voltage is +9V minus the base/emitter junction voltage with is
        > around 0.7V. So, with +8.3 volts on the emitter, emitter current
        > (using a 1k resistor) will be 8.3 volts divided by 1k with equals
        > 8.3mA. You don't want to go much below 5mA as the RF stage will
        > then be subject to AM detection (strong AM band stations will cause
        > the transistor's emitter/base junction to AM detect..with then over
        > rides the shortwave you are trying to receive). I've seen a lot of
        > published RF stages with use traps to try to prevent this but much
        > simpler just to run RF stage current high enough to prevent this.
        > So..bottom line: just take desired supply voltage minus 0.7V and
        > divide 8mA into it to find new value for emitter resistor. Easy.
        >
        > 73 DE N1TEV
        >
        >
        >
        >
        >
        > --- In regenrx@yahoogroups.com, "Bill Jones" <kd7s@p...> wrote:
        >>
        >> Hello Friends,
        >>
        >> I have been having a ball with Charles Kitchin's "A Simple Regen
        > Radio for
        >> Beginners" from the September, 2000, issue of QST. I set my
        > version up to
        >> tune the 31 meter band which also gets WWV and the 30 meter ham
        > band.
        >>
        >> I want to build another one but I'd like to add a simple r.f.
        > amplifier.
        >> I'm not interested in the additional gain as much as I am
        > isolating the
        >> antenna from the main tank circuit. Instead of using a
        > telescoping whip as
        >> suggested in the original article I substituted a 36" piece of
        > wire. It
        >> works well but as the wire moves or the length changes, so does
        > the
        >> frequency response of the radio.
        >>
        >> Has anyone "been there, done that?"
        >> ========================
        >> Bill Jones KD7S <><
        >> http://www.psnw.com/~kd7s
        >> Sanger, California
        >> ========================
        >>
        >
        >
        >
        >
        >
        >
        >
        >
        > "In the interest of Regenerating radio's lost art of Regeneration"
        > Yahoo! Groups Links
        >
        >
        >
        >
        >
        >
        >
      • harry lee
        Why are you useing a 2N2222 and not a FET since this should be a high impedance circuit? Bill Jones wrote: Many thanks, Charles, for
        Message 3 of 8 , Dec 1, 2005
          Why are you useing a 2N2222 and not a FET since this should be a high impedance circuit?


          Bill Jones <kd7s@...> wrote: Many thanks, Charles, for suggesting an r.f. amp for the Sept. 2000, QST
          regen. From your description I have drawn a schematic and posted it on my
          web site. As time permits, would you please click on the link below to make
          sure I followed your description correctly. If it is drawn correctly I will
          upload it to the files area of this group. Again, thank you for your help
          and generosity.

          http://www.psnw.com/~kd7s/RegenRFamp.jpg
          ========================
          Bill Jones KD7S <><
          http://www.psnw.com/~kd7s
          Sanger, California
          ========================
          ----- Original Message -----
          From: "n1tev" <n1tev@...>
          To: <regenrx@yahoogroups.com>
          Sent: Thursday, December 01, 2005 9:39 AM
          Subject: [regenrx] Re: Regen Antenna Isolation


          > Hi Bill (and the group),
          > I've come up with a very simple and useful RF amplifier for both
          > solid state and tube regens. I've been meaning to write this up and
          > (hopefully) publish the circuit in QST magazine.
          >
          > With regens, it's VERY important to use an RF stage that's simple,
          > stable, and broadband. If you try to add a tuned RF stage it's
          > extremely difficult to get the thing to "track" the hi Q (Q
          > multiplied) LC circuits in a regen, so it's better to use an untuned
          > circuit.
          >
          > Here's my RF stage. This simple add-on circuit will completely
          > eliminate the hand capacitance detuning effect found on the QST
          > simple regen. It's a grounded base RF amp with a fair amount of
          > gain and isolation. This was designed for use with the
          > QST "Beginner's regen" circuit but should work well with any regen
          > needing an RF stage for antenna isolation.
          >
          > Use a 2N2222 transistor. From emitter through a 1k resistor to
          > ground. Also from emitter through something big (like a 0.01
          > microFarad) cap to whip antenna. If external antenna is used run
          > through about 5PF to antenna from emitter. Base is 0.01 microFarad
          > cap to ground and also from base directly to +9V. From collector
          > through ANY RFC around 1 millihenry: you can drop in a lot of RFCs
          > into this with no real change as RF stage is driving the VERY hi Z
          > tank of a regen circuit. Then from collector again through a 5pF cap
          > to the top of the coil in the regen (also the tuning cap with the
          > simple regen). Now...a 5pF value is OK for the QST beginner's regen
          > but with other sets, this value should be changed to get the best
          > performance. You can use two tightly twisted wires as a coupling
          > cap or substitute cap values as you prefer. With the set running
          > increase cap value until set detunes or otherwise does not go
          > cleanly into oscillation. Couple-in as much signal as you can
          > WITHOUT increasing the detuning: the regen oscillation point should
          > still be "sharp" (no "fuzz" in sound at threshold).
          >
          > If you are coupling into an input winding or something other than a
          > Hi-Z LC tank you may need 50pF or so..just experiment.
          >
          > For a tube regen, just run the 6.3V filament voltage through a 100
          > Ohm resistor to a 100 MicroFarad (or greater) filter cap. This will
          > give you about +9V to power the circuit.
          >
          > If you operate the RF amplifier on voltages other than +9V you will
          > (probably) want to change the emitter resistor value. The emitter
          > voltage is +9V minus the base/emitter junction voltage with is
          > around 0.7V. So, with +8.3 volts on the emitter, emitter current
          > (using a 1k resistor) will be 8.3 volts divided by 1k with equals
          > 8.3mA. You don't want to go much below 5mA as the RF stage will
          > then be subject to AM detection (strong AM band stations will cause
          > the transistor's emitter/base junction to AM detect..with then over
          > rides the shortwave you are trying to receive). I've seen a lot of
          > published RF stages with use traps to try to prevent this but much
          > simpler just to run RF stage current high enough to prevent this.
          > So..bottom line: just take desired supply voltage minus 0.7V and
          > divide 8mA into it to find new value for emitter resistor. Easy.
          >
          > 73 DE N1TEV
          >
          >
          >
          >
          >
          > --- In regenrx@yahoogroups.com, "Bill Jones" <kd7s@p...> wrote:
          >>
          >> Hello Friends,
          >>
          >> I have been having a ball with Charles Kitchin's "A Simple Regen
          > Radio for
          >> Beginners" from the September, 2000, issue of QST. I set my
          > version up to
          >> tune the 31 meter band which also gets WWV and the 30 meter ham
          > band.
          >>
          >> I want to build another one but I'd like to add a simple r.f.
          > amplifier.
          >> I'm not interested in the additional gain as much as I am
          > isolating the
          >> antenna from the main tank circuit. Instead of using a
          > telescoping whip as
          >> suggested in the original article I substituted a 36" piece of
          > wire. It
          >> works well but as the wire moves or the length changes, so does
          > the
          >> frequency response of the radio.
          >>
          >> Has anyone "been there, done that?"
          >> ========================
          >> Bill Jones KD7S <><
          >> http://www.psnw.com/~kd7s
          >> Sanger, California
          >> ========================
          >>
          >
          >
          >
          >
          >
          >
          >
          >
          > "In the interest of Regenerating radio's lost art of Regeneration"
          > Yahoo! Groups Links
          >
          >
          >
          >
          >
          >
          >




          "In the interest of Regenerating radio's lost art of Regeneration"



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        • Bill Jones
          Hi Harry, ... While the input impedance is fairly, the output impedance should be quite high. The purpose here is not so much to provide a ton of gain but
          Message 4 of 8 , Dec 1, 2005
            Hi Harry,

            You wrote:
            > Why are you useing a 2N2222 and not a FET since this should be a high
            > impedance circuit?

            While the input impedance is fairly, the output impedance should be quite
            high. The purpose here is not so much to provide a ton of gain but rather
            to isolate the antenna from the tuned circuit in the regen receiver.

            While we're on the subject, I removed the schematic I drew from my web page
            because Charles Kitchen was working on a QST article and didn't want his
            design to be published on the Internet. I am sincerely sorry I put it up
            there without asking permission.
            ========================
            Bill Jones KD7S <><
            http://www.psnw.com/~kd7s
            Sanger, California
            ========================
          • n1tev
            A bipolar transistor and a JFET have about the same (high) output impedance. Less than a sreeen grid tube but OK if a small coupling cap is used between the RF
            Message 5 of 8 , Dec 2, 2005
              A bipolar transistor and a JFET have about the same (high) output
              impedance. Less than a sreeen grid tube but OK if a small coupling
              cap is used between the RF stage collector and the LC tank of the
              regen. Their INPUT impedance is quite different though and this is
              why I use the 2N2222 in a grounded base connection. This has a
              number of advantages: first, there is no Miller effect, as you would
              get with a common emitter connection. Second, the input impedance is
              low, good for resisting AM detection on strong stations and for a
              reasonable antenna match. Third, a common base connection has a
              very wide frequency response and a very high output impedance.
              Finally, common base has very high stability and won't oscillate.

              --- In regenrx@yahoogroups.com, harry lee <elhen704@y...> wrote:
              >
              > Why are you useing a 2N2222 and not a FET since this should be a
              high impedance circuit?
              >
              >
              > Bill Jones <kd7s@p...> wrote: Many thanks, Charles, for
              suggesting an r.f. amp for the Sept. 2000, QST
              > regen. From your description I have drawn a schematic and posted
              it on my
              > web site. As time permits, would you please click on the link
              below to make
              > sure I followed your description correctly. If it is drawn
              correctly I will
              > upload it to the files area of this group. Again, thank you for
              your help
              > and generosity.
              >
              > http://www.psnw.com/~kd7s/RegenRFamp.jpg
              > ========================
              > Bill Jones KD7S <><
              > http://www.psnw.com/~kd7s
              > Sanger, California
              > ========================
              > ----- Original Message -----
              > From: "n1tev" <n1tev@y...>
              > To: <regenrx@yahoogroups.com>
              > Sent: Thursday, December 01, 2005 9:39 AM
              > Subject: [regenrx] Re: Regen Antenna Isolation
              >
              >
              > > Hi Bill (and the group),
              > > I've come up with a very simple and useful RF amplifier for both
              > > solid state and tube regens. I've been meaning to write this
              up and
              > > (hopefully) publish the circuit in QST magazine.
              > >
              > > With regens, it's VERY important to use an RF stage that's
              simple,
              > > stable, and broadband. If you try to add a tuned RF stage it's
              > > extremely difficult to get the thing to "track" the hi Q (Q
              > > multiplied) LC circuits in a regen, so it's better to use an
              untuned
              > > circuit.
              > >
              > > Here's my RF stage. This simple add-on circuit will completely
              > > eliminate the hand capacitance detuning effect found on the QST
              > > simple regen. It's a grounded base RF amp with a fair amount of
              > > gain and isolation. This was designed for use with the
              > > QST "Beginner's regen" circuit but should work well with any
              regen
              > > needing an RF stage for antenna isolation.
              > >
              > > Use a 2N2222 transistor. From emitter through a 1k resistor to
              > > ground. Also from emitter through something big (like a 0.01
              > > microFarad) cap to whip antenna. If external antenna is used
              run
              > > through about 5PF to antenna from emitter. Base is 0.01
              microFarad
              > > cap to ground and also from base directly to +9V. From collector
              > > through ANY RFC around 1 millihenry: you can drop in a lot of
              RFCs
              > > into this with no real change as RF stage is driving the VERY
              hi Z
              > > tank of a regen circuit. Then from collector again through a
              5pF cap
              > > to the top of the coil in the regen (also the tuning cap with
              the
              > > simple regen). Now...a 5pF value is OK for the QST beginner's
              regen
              > > but with other sets, this value should be changed to get the
              best
              > > performance. You can use two tightly twisted wires as a
              coupling
              > > cap or substitute cap values as you prefer. With the set
              running
              > > increase cap value until set detunes or otherwise does not go
              > > cleanly into oscillation. Couple-in as much signal as you can
              > > WITHOUT increasing the detuning: the regen oscillation point
              should
              > > still be "sharp" (no "fuzz" in sound at threshold).
              > >
              > > If you are coupling into an input winding or something other
              than a
              > > Hi-Z LC tank you may need 50pF or so..just experiment.
              > >
              > > For a tube regen, just run the 6.3V filament voltage through a
              100
              > > Ohm resistor to a 100 MicroFarad (or greater) filter cap. This
              will
              > > give you about +9V to power the circuit.
              > >
              > > If you operate the RF amplifier on voltages other than +9V you
              will
              > > (probably) want to change the emitter resistor value. The
              emitter
              > > voltage is +9V minus the base/emitter junction voltage with is
              > > around 0.7V. So, with +8.3 volts on the emitter, emitter
              current
              > > (using a 1k resistor) will be 8.3 volts divided by 1k with
              equals
              > > 8.3mA. You don't want to go much below 5mA as the RF stage will
              > > then be subject to AM detection (strong AM band stations will
              cause
              > > the transistor's emitter/base junction to AM detect..with then
              over
              > > rides the shortwave you are trying to receive). I've seen a
              lot of
              > > published RF stages with use traps to try to prevent this but
              much
              > > simpler just to run RF stage current high enough to prevent
              this.
              > > So..bottom line: just take desired supply voltage minus 0.7V and
              > > divide 8mA into it to find new value for emitter resistor.
              Easy.
              > >
              > > 73 DE N1TEV
              > >
              > >
              > >
              > >
              > >
              > > --- In regenrx@yahoogroups.com, "Bill Jones" <kd7s@p...> wrote:
              > >>
              > >> Hello Friends,
              > >>
              > >> I have been having a ball with Charles Kitchin's "A Simple
              Regen
              > > Radio for
              > >> Beginners" from the September, 2000, issue of QST. I set my
              > > version up to
              > >> tune the 31 meter band which also gets WWV and the 30 meter ham
              > > band.
              > >>
              > >> I want to build another one but I'd like to add a simple r.f.
              > > amplifier.
              > >> I'm not interested in the additional gain as much as I am
              > > isolating the
              > >> antenna from the main tank circuit. Instead of using a
              > > telescoping whip as
              > >> suggested in the original article I substituted a 36" piece of
              > > wire. It
              > >> works well but as the wire moves or the length changes, so does
              > > the
              > >> frequency response of the radio.
              > >>
              > >> Has anyone "been there, done that?"
              > >> ========================
              > >> Bill Jones KD7S <><
              > >> http://www.psnw.com/~kd7s
              > >> Sanger, California
              > >> ========================
              > >>
              > >
              > >
              > >
              > >
              > >
              > >
              > >
              > >
              > > "In the interest of Regenerating radio's lost art of
              Regeneration"
              > > Yahoo! Groups Links
              > >
              > >
              > >
              > >
              > >
              > >
              > >
              >
              >
              >
              >
              > "In the interest of Regenerating radio's lost art of
              Regeneration"
              >
              >
              >
              > SPONSORED LINKS
              > Old timer
              knife Old timer
              knifes Craft
              hobby
              Hobbies and crafts Ham
              radio antenna Ham
              radio

              >
              > ---------------------------------
              > YAHOO! GROUPS LINKS
              >
              >
              > Visit your group "regenrx" on the web.
              >
              > To unsubscribe from this group, send an email to:
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              >
              > Your use of Yahoo! Groups is subject to the Yahoo! Terms of
              Service.
              >
              >
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              >
              >
              >
              >
              >
              >
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              >
              > [Non-text portions of this message have been removed]
              >
            • n1tev
              Hi Bill, Thanks. By the way, I m wondering why I ve never seen grounded gate triode RF stages in regen circuits from years past. Even when they used screen
              Message 6 of 8 , Dec 2, 2005
                Hi Bill,
                Thanks. By the way, I'm wondering why I've never seen grounded gate
                triode RF stages in regen circuits from years past. Even when they
                used screen grid tubes, the circuits I've seen all were tuned RF
                stages. Miller capacitance (the modulation of input capacitance as
                you try to get gain in a common cathode triode amplifier) always
                limited a triode stage to very low RF gain or even a loss at Ham
                band frequencies. But with grounded grid (or grounded base,
                grounded gate, etc) there is no Miller effect because the grid is
                grounded; also there is now reasonable isolation between output and
                input of the RF stage, making it more effective.

                The use of a tuned RF stage really adds complexity: the coil in the
                RF stage has a normal Q..maybe a hundred or so but the regen's coil
                (and cap) are Q multiplied by about 1000 times. So..what you have
                made here is a gain stage (the RF amplifier) with a tuned LC circuit
                at its input and the regen circuit's high Q tank is at its output.
                Two tuned LC circuits with gain in between is almost guaranteed to
                oscillate (tuned grid-tuned plate oscillator). So operating
                grounded base (grounded grid, grounded gate etc) is much better.

                Antenna isolation is really important in a regen for many reasons.
                At higher short wave frequencies you can get bad "hum modulation"
                from RF feeding out to the antenna from the detector. The only bad
                thing about adding an RF stage to a regen is that you must insure
                that there is no detector loading. The ideal case would be variable
                coupling between RF stage and detector so you can change the amount
                of coupling when you change bands. But...I've found that this is
                hard to do: there is always some RF feedthrough to ground or around
                the circuit when you add these parts (a variable cap or a rotary
                switch with fixed caps) between RF stage and detector. This usually
                adds losses which cause the regen to detune ior otherwise operate
                erratically as the regen goes through its oscillation point.

                73 DE N1TEV

                --- In regenrx@yahoogroups.com, "Bill Jones" <kd7s@p...> wrote:
                >
                > Hi Harry,
                >
                > You wrote:
                > > Why are you useing a 2N2222 and not a FET since this should be a
                high
                > > impedance circuit?
                >
                > While the input impedance is fairly, the output impedance should
                be quite
                > high. The purpose here is not so much to provide a ton of gain
                but rather
                > to isolate the antenna from the tuned circuit in the regen
                receiver.
                >
                > While we're on the subject, I removed the schematic I drew from my
                web page
                > because Charles Kitchen was working on a QST article and didn't
                want his
                > design to be published on the Internet. I am sincerely sorry I
                put it up
                > there without asking permission.
                > ========================
                > Bill Jones KD7S <><
                > http://www.psnw.com/~kd7s
                > Sanger, California
                > ========================
                >
              • Gary Johanson
                The ARRL handbooks show a few grounded gate RF amps using MPF-102s. One i recall is in the 1977 handbook for the DC Kilogram rx. I borrowed that one for a
                Message 7 of 8 , Dec 2, 2005
                  The ARRL handbooks show a few grounded gate RF amps using MPF-102s.
                  One i recall is in the 1977 handbook for the DC Kilogram rx. I
                  borrowed that one for a regen sometime back. (vid 1977 ARRL Handbook,
                  pgs 338-339)

                  Someone may want to check me out, but i think that 2m superregen
                  built in the metal card-file box in the 1980 handbook also uses a
                  grounded gate or base RF amp, too. Grounded grid amps are indeed
                  rare for HF receiver of the Hollow State persuasion. But i think i
                  have seen a few 6C4's and 6N7s used recently, not including Andy's.

                  An RF stage need not be complex at all, in fact the ones used in the
                  1920s and 30s are quite simple and effective. One thing was that the
                  224 was a low gain device, kept loosely coupled with untuned output,
                  which went a long way towards preventing oscillation. ( many of the
                  early RF amps were totally untuned, serving as isolation devices
                  only, something i wouldn't recommend these days.)

                  I believe the RF stages in the RAL are configured similarly, inputs
                  being tuned only.

                  In my regens, i use a very simple 6J7 or 6K7 pentode RF amp with no
                  problem. I double tune the input and leave the output untuned. The
                  output is somewhat loosely coupled to the grid LC of the detector, in
                  much the same way as the SW3. Overall RF stage gain is marginal,
                  which is good. The detector is sensitive enough as it is. In fact:
                  i can inject a signal from a local oscillator to the cathode of this
                  RF amp (lifting it above ground by a 1000 ohm resistor) thru a .001
                  cap, and pull the difference frequency using the regen detector
                  alone, without the output being tuned to the sum or difference
                  frequency. If the IF is wide enough, the regen detector is selective
                  enough not to be bothered by the opposing product. 2 to 3mc IF is
                  more than sufficient. Which is why the Regenerodyne works so well.

                  gary // wd4nka
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