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SGC 237 Tuning Trouble

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  • Mike Miranda W4DXL
    I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I upgraded my rig which means I also had to get a different tuner. I bought the SGC-237
    Message 1 of 12 , Jan 2, 2010
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      I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I upgraded my rig which means I also had to get a different tuner. I bought the SGC-237 so that I could share it with other rigs.

      At first there was RF all over the shack then I shortened the 12V line and that helped. The 237 still can't tune the G5RV on 80 meters. The FC-800 never had this problem. I am ready to take the 237 out and do the lightbulb test.

      I would appreciate any ideas anyone has on this.
    • jonie41
      ... Hi Mike, Happy New Year... I use an SGC-237 as well and have not had any problems with mine as far as RF is concerned. If the impedance tuning range of
      Message 2 of 12 , Jan 2, 2010
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        Mike Miranda W4DXL wrote:
        >
        > I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I
        > upgraded my rig which means I also had to get a different tuner. I
        > bought the SGC-237 so that I could share it with other rigs.
        >
        > At first there was RF all over the shack then I shortened the 12V line
        > and that helped. The 237 still can't tune the G5RV on 80 meters. The
        > FC-800 never had this problem. I am ready to take the 237 out and do
        > the lightbulb test.
        >
        > I would appreciate any ideas anyone has on this.
        >
        >
        Hi Mike,

        Happy New Year...

        I use an SGC-237 as well and have not had any problems with mine as far
        as RF is concerned.

        If the impedance tuning range of both of those couplers is similar then
        the 237 should work for you.

        My setup is a bit different though, my antenna is a 43 foot vertical
        with 32 radials each 32 feet long (till I cut the grass after the last
        radial was installed).
        My 237 is mounted to the radial plate using tubing for spacers and nuts
        and bolts of stainless steel. I feed the 237 with about 100 feet of 18
        gauge speaker wire. The feed line is RG-213 buried about 2 to 3 inches,
        the feed line that comes with the 237 is coiled up about 3 inches in
        dia. I got my 237 off of eBay and there was a ferrite on the
        power/control wires but I removed it as I was using the 237 mobile at
        that time.

        Perhaps I have accidentally installed a choke by coiling up the 237's
        included 7 foot feed line.

        Good luck with the 237, 73 John, VE3KKQ
      • Mike Miranda W4DXL
        John, You just described what I want to do eventually. I have been looking at the DX Engineering 43 foot. That has to wait at least until spring when the
        Message 3 of 12 , Jan 2, 2010
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          John,

          You just described what I want to do eventually. I have been looking at the DX Engineering 43 foot. That has to wait at least until spring when the weather is warmer and I hopefully have some more money to spend. I thought it would work with the G5RV in the meantime.

          Thanks for your comments.

          73,
          Mike W4DXL

          --- In Smartuners@yahoogroups.com, jonie41 <jonie41@...> wrote:
          >
          > Mike Miranda W4DXL wrote:
          > >
          > > I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I
          > > upgraded my rig which means I also had to get a different tuner. I
          > > bought the SGC-237 so that I could share it with other rigs.
          > >
          > > At first there was RF all over the shack then I shortened the 12V line
          > > and that helped. The 237 still can't tune the G5RV on 80 meters. The
          > > FC-800 never had this problem. I am ready to take the 237 out and do
          > > the lightbulb test.
          > >
          > > I would appreciate any ideas anyone has on this.
          > >
          > >
          > Hi Mike,
          >
          > Happy New Year...
          >
          > I use an SGC-237 as well and have not had any problems with mine as far
          > as RF is concerned.
          >
          > If the impedance tuning range of both of those couplers is similar then
          > the 237 should work for you.
          >
          > My setup is a bit different though, my antenna is a 43 foot vertical
          > with 32 radials each 32 feet long (till I cut the grass after the last
          > radial was installed).
          > My 237 is mounted to the radial plate using tubing for spacers and nuts
          > and bolts of stainless steel. I feed the 237 with about 100 feet of 18
          > gauge speaker wire. The feed line is RG-213 buried about 2 to 3 inches,
          > the feed line that comes with the 237 is coiled up about 3 inches in
          > dia. I got my 237 off of eBay and there was a ferrite on the
          > power/control wires but I removed it as I was using the 237 mobile at
          > that time.
          >
          > Perhaps I have accidentally installed a choke by coiling up the 237's
          > included 7 foot feed line.
          >
          > Good luck with the 237, 73 John, VE3KKQ
          >
        • Christopher E. Brown
          ... Describe your feed. As I recall the G5RV is a 102ft doublet fed through a 450ohm window line matching section and coax. This would not fit with feeding
          Message 4 of 12 , Jan 2, 2010
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            On Sat, 2 Jan 2010, Mike Miranda W4DXL wrote:

            > I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I upgraded my rig which means I also had to get a different tuner. I bought the SGC-237 so that I could share it with other rigs.
            >
            > At first there was RF all over the shack then I shortened the 12V line and that helped. The 237 still can't tune the G5RV on 80 meters. The FC-800 never had this problem. I am ready to take the 237 out and do the lightbulb test.
            >
            > I would appreciate any ideas anyone has on this.




            Describe your feed.


            As I recall the G5RV is a 102ft doublet fed through a 450ohm window line
            matching section and coax. This would not fit with feeding through a SGC.




            Is it a 102ft doublet?


            How high?


            Is it straight, bent, flat-top, zigzag?


            How far i the antenna from the shack and house wiring?



            I have played with my 237s and balanced antennas with good luck, both with
            the 237 at the center of the antenna and below feeding through 450 window
            line.


            The key points for a balanced antenna



            Stiff common mode choke is needed on the coax/control lines. Without one,
            the coax shield is operating in parallel with one ide of the doublet. RF
            in the shack and hosed pattern. RF likely to be getting back into the
            control lines.


            On at last some bands the antenna will present a high impedance, making a
            much higher value choke a requirement as compared to a dipole or vertical
            presenting a 30 - 80 ohm feedpoint impedance.

            By stiff I mean 3 - 5 kohm minimum 80 - 10M.



            The antenna itself may need some minor trimming. There are step limits
            due to the fixed inductors/caps, is the issue *all* of 75/80 or just one
            part? I have had issues with antennas in the 30 - 70 resist range with a
            few hundred reactive.



            Feedline... If you are using a feedline, remember it will be a
            transmission line tranformer... You may need to model or field test
            adding/removing a little.

            If your antenna was say 40 -j350 on 3.75 at the feedpoint, say 87 feet of
            450 window would give around 5500 +j 2800 at the tuner. Not too hard to
            transform to something the coupler may have issues with, specially if the
            coupler is unchoked.


            If the 237 is behaving well on other bands it is almost certainly an issue
            outside the coupler.
          • Mike Miranda W4DXL
            Christopher
            Message 5 of 12 , Jan 2, 2010
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              Christopher<

              Look for my answers between your questions, thanks for your input.

              >
              >
              > Describe your feed.

              G5RV just about roof level with 30 feet of ladder line as the feed line going into the tuner

              >
              > As I recall the G5RV is a 102ft doublet fed through a 450ohm window line
              > matching section and coax. This would not fit with feeding through a SGC.

              102 foot dipole actually through a 450 ohm window line, that connects directly to the tuner as shown in one of the illustrations in the file section (see ladderline.jpg in the files section to see what it looks like.)


              >
              > How high?

              about 25 feet above ground
              >
              > Is it straight, bent, flat-top, zigzag?

              straight
              >
              > How far i the antenna from the shack and house wiring?

              Ladder line comes down along side the house tuner is located under the house. The antenna runs just above the roof peak.
              >
              >
              > I have played with my 237s and balanced antennas with good luck, both with
              > the 237 at the center of the antenna and below feeding through 450 window
              > line.
              >
              This same antenna worked very well with the FC-800 Yaesu remote auto tuner. Also the tuner would not tune a light bulb on 40 meters for 80 meters which is the test that SGC asks you to do. I tried it with a 60 watt bulb and a 75 watt bulb with the same results. The tuner kept tuning for 25 seconds without coming up with a match. Unkey the mic and key it again and it tries to find a match for 25 seconds before giving up.

              73,
              Mike W4DXL
            • Christopher E. Brown
              I have a similar setup, but it is 36ft window line to a 50ft doublet. You want to be careful about spacing and insulation, and run a common mode choke on the
              Message 6 of 12 , Jan 3, 2010
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                I have a similar setup, but it is 36ft window line to a 50ft doublet. You
                want to be careful about spacing and insulation, and run a common mode
                choke on the coax/control entering the 237 but otherwise is simple. I
                used 4 inch j hooks (plastic cable hooks commonly used in datacom cabling)
                to space the window line off the wall and the trusses. Where it passes
                through the ceiling I used a plastic outlet box and blank cover, slotted
                in the center. Be aware of where flashing is used in the roof. Running
                ladder close to 8 inch wide copper or tin flashing can make it untunable.




                But, in this case it sounds like a coupler issue to me. I just ran the
                bulb test myself, using standard 60, 75 and 100w bulbs (standard tungsten
                filament of course, not CFL). No issues, 160M - 6M.


                I would check voltage levels before calling SGC, but that is the last
                thing I can think of. A bad connection causing bouncing voltage levels as
                the relays cycle could throw things off, or low voltage in general can
                cause issues.



                On Sun, 3 Jan 2010, Mike Miranda W4DXL wrote:

                > Christopher<
                >
                > Look for my answers between your questions, thanks for your input.
                >
                >>
                >>
                >> Describe your feed.
                >
                > G5RV just about roof level with 30 feet of ladder line as the feed line going into the tuner
                >
                >>
                >> As I recall the G5RV is a 102ft doublet fed through a 450ohm window line
                >> matching section and coax. This would not fit with feeding through a SGC.
                >
                > 102 foot dipole actually through a 450 ohm window line, that connects directly to the tuner as shown in one of the illustrations in the file section (see ladderline.jpg in the files section to see what it looks like.)
                >
                >
                >>
                >> How high?
                >
                > about 25 feet above ground
                >>
                >> Is it straight, bent, flat-top, zigzag?
                >
                > straight
                >>
                >> How far i the antenna from the shack and house wiring?
                >
                > Ladder line comes down along side the house tuner is located under the house. The antenna runs just above the roof peak.
                >>
                >>
                >> I have played with my 237s and balanced antennas with good luck, both with
                >> the 237 at the center of the antenna and below feeding through 450 window
                >> line.
                >>
                > This same antenna worked very well with the FC-800 Yaesu remote auto tuner. Also the tuner would not tune a light bulb on 40 meters for 80 meters which is the test that SGC asks you to do. I tried it with a 60 watt bulb and a 75 watt bulb with the same results. The tuner kept tuning for 25 seconds without coming up with a match. Unkey the mic and key it again and it tries to find a match for 25 seconds before giving up.
                >
                > 73,
                > Mike W4DXL
                >
                >
                >
                > ------------------------------------
                >
                > Yahoo! Groups Links
                >
                >
                >
              • Mike Miranda W4DXL
                Thanks for testing your tuner. Yes I was sure to use standard tungsten bulbs as well since I didn t know what the CFL bulbs would do, I assume they wouldn t
                Message 7 of 12 , Jan 3, 2010
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                  Thanks for testing your tuner. Yes I was sure to use standard tungsten bulbs as well since I didn't know what the CFL bulbs would do, I assume they wouldn't work properly. I took the tuner out for my test and ran it inside where it's warm. All connections were tight.

                  I'll call HRO first, and hope they will swap it out. The tuner is brand new.

                  73,
                  Mike W4DXL

                  --- In Smartuners@yahoogroups.com, "Christopher E. Brown" <cbrown@...> wrote:
                  >
                  >
                  >
                  > I have a similar setup, but it is 36ft window line to a 50ft doublet. You
                  > want to be careful about spacing and insulation, and run a common mode
                  > choke on the coax/control entering the 237 but otherwise is simple. I
                  > used 4 inch j hooks (plastic cable hooks commonly used in datacom cabling)
                  > to space the window line off the wall and the trusses. Where it passes
                  > through the ceiling I used a plastic outlet box and blank cover, slotted
                  > in the center. Be aware of where flashing is used in the roof. Running
                  > ladder close to 8 inch wide copper or tin flashing can make it untunable.
                  >
                  >
                  >
                  >
                  > But, in this case it sounds like a coupler issue to me. I just ran the
                  > bulb test myself, using standard 60, 75 and 100w bulbs (standard tungsten
                  > filament of course, not CFL). No issues, 160M - 6M.
                  >
                  >
                  > I would check voltage levels before calling SGC, but that is the last
                  > thing I can think of. A bad connection causing bouncing voltage levels as
                  > the relays cycle could throw things off, or low voltage in general can
                  > cause issues.
                  >
                  >
                  >
                  > On Sun, 3 Jan 2010, Mike Miranda W4DXL wrote:
                  >
                  > > Christopher<
                  > >
                  > > Look for my answers between your questions, thanks for your input.
                  > >
                  > >>
                  > >>
                  > >> Describe your feed.
                  > >
                  > > G5RV just about roof level with 30 feet of ladder line as the feed line going into the tuner
                  > >
                  > >>
                  > >> As I recall the G5RV is a 102ft doublet fed through a 450ohm window line
                  > >> matching section and coax. This would not fit with feeding through a SGC.
                  > >
                  > > 102 foot dipole actually through a 450 ohm window line, that connects directly to the tuner as shown in one of the illustrations in the file section (see ladderline.jpg in the files section to see what it looks like.)
                  > >
                  > >
                  > >>
                  > >> How high?
                  > >
                  > > about 25 feet above ground
                  > >>
                  > >> Is it straight, bent, flat-top, zigzag?
                  > >
                  > > straight
                  > >>
                  > >> How far i the antenna from the shack and house wiring?
                  > >
                  > > Ladder line comes down along side the house tuner is located under the house. The antenna runs just above the roof peak.
                  > >>
                  > >>
                  > >> I have played with my 237s and balanced antennas with good luck, both with
                  > >> the 237 at the center of the antenna and below feeding through 450 window
                  > >> line.
                  > >>
                  > > This same antenna worked very well with the FC-800 Yaesu remote auto tuner. Also the tuner would not tune a light bulb on 40 meters for 80 meters which is the test that SGC asks you to do. I tried it with a 60 watt bulb and a 75 watt bulb with the same results. The tuner kept tuning for 25 seconds without coming up with a match. Unkey the mic and key it again and it tries to find a match for 25 seconds before giving up.
                  > >
                  > > 73,
                  > > Mike W4DXL
                  > >
                  > >
                  > >
                  > > ------------------------------------
                  > >
                  > > Yahoo! Groups Links
                  > >
                  > >
                  > >
                  >
                • Randy Farmer
                  This sounds like one or more bad relays in the tuner to me. It could also be the result of an electronics problem with the relay drivers. It s definitely not
                  Message 8 of 12 , Jan 3, 2010
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                    This sounds like one or more bad relays in the tuner to me. It could
                    also be the result of an electronics problem with the relay drivers.
                    It's definitely not normal. The 237 should have no problem tuning
                    your antenna, and if the light bulb test fails there's absolutely
                    something wrong with the tuner.

                    73...
                    Randy, W8FN

                    >G5RV just about roof level with 30 feet of ladder line as the feed
                    >line going into the tuner
                    >
                    >102 foot dipole actually through a 450 ohm window line, that
                    >connects directly to the tuner as shown in one of the illustrations
                    >in the file section (see ladderline.jpg in the files section to see
                    >what it looks like.)
                    >
                    >about 25 feet above ground
                    >
                    >straight
                    >
                    >Ladder line comes down along side the house tuner is located under
                    >the house. The antenna runs just above the roof peak.


                    >This same antenna worked very well with the FC-800 Yaesu remote auto
                    >tuner. Also the tuner would not tune a light bulb on 40 meters for
                    >80 meters which is the test that SGC asks you to do. I tried it with
                    >a 60 watt bulb and a 75 watt bulb with the same results. The tuner
                    >kept tuning for 25 seconds without coming up with a match. Unkey the
                    >mic and key it again and it tries to find a match for 25 seconds
                    >before giving up.
                  • James Skalski
                    Is it my imagination are are a lot of people having problems with these SGC tuners? It seems that a lot are replacing the CPU and others are adding chokes.
                    Message 9 of 12 , Jan 3, 2010
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                      Is it my imagination are are a lot of people having problems with these SGC tuners?
                      It seems that a lot are replacing the CPU and others are adding chokes. Couldn't this also be remedied by more reliable design? You would think that with so many failing the CPU would be less expensive.
                      The design seems to be very closely copied from an RSGB series called the Picatune. The only exception seems that the original didn't have control lines as the voltages were sent along the coax. The original also had a large high Q coil and the homemade capacitors handled up to 400 watts.  Here the original seems more robust than the copy.
                      Jim n2go

                      --- On Sun, 1/3/10, Randy Farmer <w8fn@...> wrote:

                      From: Randy Farmer <w8fn@...>
                      Subject: Re: [Smartuners] Re: SGC 237 Tuning Trouble
                      To: Smartuners@yahoogroups.com
                      Date: Sunday, January 3, 2010, 9:56 AM

                      This sounds like one or more bad relays in the tuner to me. It could
                      also be the result of an electronics problem with the relay drivers.
                      It's definitely not normal. The 237 should have no problem tuning
                      your antenna, and if the light bulb test fails there's absolutely
                      something wrong with the tuner.

                      73...
                      Randy, W8FN

                      >G5RV just about roof level with 30 feet of ladder line as the feed
                      >line going into the tuner
                      >
                      >102 foot dipole actually through a 450 ohm window line, that
                      >connects directly to the tuner as shown in one of the illustrations
                      >in the file section (see ladderline.jpg in the files section to see
                      >what it looks like.)
                      >
                      >about 25 feet above ground
                      >
                      >straight
                      >
                      >Ladder line comes down along side the house tuner is located under
                      >the house. The antenna runs just above the roof peak.


                      >This same antenna worked very well with the FC-800 Yaesu remote auto
                      >tuner. Also the tuner would not tune a light bulb on 40 meters for
                      >80 meters which is the test that SGC asks you to do. I tried it with
                      >a 60 watt bulb and a 75 watt bulb with the same results. The tuner
                      >kept tuning for 25 seconds without coming up with a match. Unkey the
                      >mic and key it again and it tries to find a match for 25 seconds
                      >before giving up.



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                    • Mike Miranda W4DXL
                      Jim, In defense of SGC I would think you d naturally hear more about problem tuners than ones that are working properly. People who have working units may
                      Message 10 of 12 , Jan 3, 2010
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                        Jim,

                        In defense of SGC I would think you'd naturally hear more about problem tuners than ones that are working properly. People who have working units may never seek out this group in the first place, at least I hope that's the way it is.

                        I hate to see problems right out of the box like this. It also makes me feel that I should home brew my own manual tuner. I'd do that but I hate the sound of guys tuning up on the air.

                        73,
                        Mike, W4DXL

                        --- In Smartuners@yahoogroups.com, James Skalski <jskalski@...> wrote:
                        >
                        > Is it my imagination are are a lot of people having problems with these SGC tuners?
                        > It seems that a lot are replacing the CPU and others are adding chokes. Couldn't this also be remedied by more reliable design? You would think that with so many failing the CPU would be less expensive.
                        > The design seems to be very closely copied from an RSGB series called the Picatune. The only exception seems that the original didn't have control lines as the voltages were sent along the coax. The original also had a large high Q coil and the homemade capacitors handled up to 400 watts.  Here the original seems more robust than the copy.
                        > Jim n2go
                        >
                        > --- On Sun, 1/3/10, Randy Farmer <w8fn@...> wrote:
                        >
                        > From: Randy Farmer <w8fn@...>
                        > Subject: Re: [Smartuners] Re: SGC 237 Tuning Trouble
                        > To: Smartuners@yahoogroups.com
                        > Date: Sunday, January 3, 2010, 9:56 AM
                        >
                        > This sounds like one or more bad relays in the tuner to me. It could
                        > also be the result of an electronics problem with the relay drivers.
                        > It's definitely not normal. The 237 should have no problem tuning
                        > your antenna, and if the light bulb test fails there's absolutely
                        > something wrong with the tuner.
                        >
                        > 73...
                        > Randy, W8FN
                        >
                        > >G5RV just about roof level with 30 feet of ladder line as the feed
                        > >line going into the tuner
                        > >
                        > >102 foot dipole actually through a 450 ohm window line, that
                        > >connects directly to the tuner as shown in one of the illustrations
                        > >in the file section (see ladderline.jpg in the files section to see
                        > >what it looks like.)
                        > >
                        > >about 25 feet above ground
                        > >
                        > >straight
                        > >
                        > >Ladder line comes down along side the house tuner is located under
                        > >the house. The antenna runs just above the roof peak.
                        >
                        >
                        > >This same antenna worked very well with the FC-800 Yaesu remote auto
                        > >tuner. Also the tuner would not tune a light bulb on 40 meters for
                        > >80 meters which is the test that SGC asks you to do. I tried it with
                        > >a 60 watt bulb and a 75 watt bulb with the same results. The tuner
                        > >kept tuning for 25 seconds without coming up with a match. Unkey the
                        > >mic and key it again and it tries to find a match for 25 seconds
                        > >before giving up.
                        >
                        >
                        >
                        > ------------------------------------
                        >
                        > Yahoo! Groups Links
                        >
                      • William
                        Christopher, Would you describe the kind of common mode choke you are using? Bill W8BC
                        Message 11 of 12 , Jan 4, 2010
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                          Christopher,
                          Would you describe the kind of common mode choke you are using?

                          Bill
                          W8BC

                          --- In Smartuners@yahoogroups.com, "Christopher E. Brown" <cbrown@...> wrote:
                          >
                          > On Sat, 2 Jan 2010, Mike Miranda W4DXL wrote:
                          >
                          > > I had a FC-800 Yaesu remote auto-tuner that tuned my G5RV just fine. I upgraded my rig which means I also had to get a different tuner. I bought the SGC-237 so that I could share it with other rigs.
                          > >
                          > > At first there was RF all over the shack then I shortened the 12V line and that helped. The 237 still can't tune the G5RV on 80 meters. The FC-800 never had this problem. I am ready to take the 237 out and do the lightbulb test.
                          > >
                          > > I would appreciate any ideas anyone has on this.
                          >
                          >
                          >
                          >
                          > Describe your feed.
                          >
                          >
                          > As I recall the G5RV is a 102ft doublet fed through a 450ohm window line
                          > matching section and coax. This would not fit with feeding through a SGC.
                          >
                          >
                          >
                          >
                          > Is it a 102ft doublet?
                          >
                          >
                          > How high?
                          >
                          >
                          > Is it straight, bent, flat-top, zigzag?
                          >
                          >
                          > How far i the antenna from the shack and house wiring?
                          >
                          >
                          >
                          > I have played with my 237s and balanced antennas with good luck, both with
                          > the 237 at the center of the antenna and below feeding through 450 window
                          > line.
                          >
                          >
                          > The key points for a balanced antenna
                          >
                          >
                          >
                          > Stiff common mode choke is needed on the coax/control lines. Without one,
                          > the coax shield is operating in parallel with one ide of the doublet. RF
                          > in the shack and hosed pattern. RF likely to be getting back into the
                          > control lines.
                          >
                          >
                          > On at last some bands the antenna will present a high impedance, making a
                          > much higher value choke a requirement as compared to a dipole or vertical
                          > presenting a 30 - 80 ohm feedpoint impedance.
                          >
                          > By stiff I mean 3 - 5 kohm minimum 80 - 10M.
                          >
                          >
                          >
                          > The antenna itself may need some minor trimming. There are step limits
                          > due to the fixed inductors/caps, is the issue *all* of 75/80 or just one
                          > part? I have had issues with antennas in the 30 - 70 resist range with a
                          > few hundred reactive.
                          >
                          >
                          >
                          > Feedline... If you are using a feedline, remember it will be a
                          > transmission line tranformer... You may need to model or field test
                          > adding/removing a little.
                          >
                          > If your antenna was say 40 -j350 on 3.75 at the feedpoint, say 87 feet of
                          > 450 window would give around 5500 +j 2800 at the tuner. Not too hard to
                          > transform to something the coupler may have issues with, specially if the
                          > coupler is unchoked.
                          >
                          >
                          > If the 237 is behaving well on other bands it is almost certainly an issue
                          > outside the coupler.
                          >
                        • Christopher E. Brown
                          ... Check out Jim Browns papers at Audio Systems Group, lots of very useful info on use on type 31 ferrite. My main invert L has 3 of the large clamp on (1in
                          Message 12 of 12 , Jan 5, 2010
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                            On Mon, 4 Jan 2010, William wrote:

                            > Christopher,
                            > Would you describe the kind of common mode choke you are using?
                            >
                            > Bill
                            > W8BC


                            Check out Jim Browns papers at Audio Systems Group, lots of very useful
                            info on use on type 31 ferrite.



                            My main invert L has 3 of the "large clamp on (1in id)", the 237 cable
                            will fit 5 turns through each with a short tail left over. This gives
                            around 6kohm at the bottom ov 80M, much higher where the L is a 1/2 wave
                            multiple on 40 and 20. Also have 7 turns through 4 2.4in toroids after
                            the coax leaves the ground about 35 feet away, and another 15ft further
                            before the cable hits the station bonding panel.


                            This is a little extreme though, and mostly for noise reduction in my
                            case.



                            Look at Jims charts for details, but I think 5 turns through a large clamp
                            plus 7 turns through 5 2.4 in toroids would be about right.

                            7 on 5 with that cable size should be 5k+ from about 1.6 to 7Mhz, and 5
                            on big clamp should be over 4k at 7mhz, climbing to 5k 15 - 20Mhz and back
                            around 4k at 30mhz.

                            Should be more than enough length to the 237 tail for this.


                            Fair-Rite P/Ns are

                            Large Clamp #31: 0431177081
                            2.4 #31 Toroid: 2631803802


                            In small lots I think the clamps are 15 - 17 each, and the toroids 8 - 10
                            USD.



                            Note, the clamp alone is about 1500ohms on 160M and 2500ohms on 10M,
                            peaking around 5000ohms near 17M. If your antenna feedpoint impedance
                            is a few hundred ohms or less on all bands of interest this alone could do
                            a decent job of it. (Rule of thumb, shoot for at least 5k on any band of
                            interest.)
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