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

RE: [Smartuners] New SG-239 behavior

Expand Messages
  • David H Hatch
    Hi Frank, I am sending your message through the group a 2nd time, as I saw no comments after the first run. it s getting to be a busy time for folks, I d
    Message 1 of 5 , Dec 3, 2007
    • 0 Attachment

      Hi Frank,

       

      I am sending your message through the group a 2nd time, as I saw no comments after the first run… it’s getting to be a busy time for folks, I’d guess…

       

      Maybe we can catch a reply this time…

       

      I have purchased a new SG-239 tuner within the last week. After
      hooking it up to an antenna and to a test setup I have come up with a
      couple of questions regarding its behavior.

      Test setup: I have an IC718 transceiver which I hooked up, through a
      MFJ941E operated in the bypass mode therefore utilizing the VSWR and
      forward power meter feature, to the SG-239. The coupling cable
      between The IC718 and MFJ VSWR meter is one foot of RG58. The output
      of the VSWR meter is hooked up to the SG239 utilizing a one foot long
      length of RG58 with 7 ferrite beads slipped over the outside of the
      cable. The antenna connections on the SG-239 is connected with "pig
      tail" clip leads on one end of a two foot long RG58 cable to a 100
      watt dummy load.

      Test results: The SG-239 matched to the dummy load with typical VSWR
      readings of < 1.5:1 as measured on both the internal IC-718 SWR meter
      and the MFJ VSWR meter except for a couple of bands. Initially a
      match on the 20 meter band was attempted using the IC-718 in the AM
      mode with 40 watt carrier. The SG-239 "clicked" a few times and
      refused to match and VSWR was > 5:1. A second attempt was made on 40
      meters and the SG-239 relays began "clicking" and a 1.1:1 match was
      quickly achieved. I returned to 20 meters and tried again and this
      time the SG-239 found a match that was < 1.5:1. I tried the other
      bands 80 through 10 meters and achieved a good match on all bands
      except 15 meters. The best match available on 15 meters was 3:1, this
      was in spite of the observation of the VSWR meter during the tuning
      process that several very good VSWR readings were found but were
      skipped over in favor of a 3:1 match.

      Antenna setup:

      (Message over 64 KB, truncated)

    • w8fn1
      Hi, Frank. The SG-239 (and all the other SGC tuners) works just fine feeding a doublet fed with ladder line. As a matter of fact, I have one in service now. I
      Message 2 of 5 , Dec 3, 2007
      • 0 Attachment
        Hi, Frank.

        The SG-239 (and all the other SGC tuners) works just fine feeding a
        doublet fed with ladder line. As a matter of fact, I have one in
        service now. I too have seen my 239 act "nervous" at times for no
        obvious reason, but it always seems to work after a couple of tries
        at matching.

        > Some antenna impedances presented to the SG-239 that I'm trying to
        match:
        >
        > 7.2 MHz: 93 -j 1616
        > 14.2 MHz: 88 -j 147
        > 18.1 MHz 279 -j 646
        > 21.4 MHz 78 +j 252
        > 28.4 MHz 73 +j 353

        These are some extremely high impedances, and would be difficult to
        match with most any kind of tuner. The limited choice of circuit
        constants available on the SG-239, especially the load side
        capacitance, makes it unlikely you will be able to match these
        loads. Looking at the schematic of the SG-239, we can see the range
        of adjustments of the transmitter side capacitance is binary
        combinations of 51pF, 100pF, 200pF, 400pF, 800pF, and 1620pF (51pF
        to 3171pF in increments of 51pF). The series L range of adjustments
        is binary combinations of 0.125uH, 0.25uH, 0.5uH, 1uH, 2uH, 4uH, and
        8uH (0.125uH to 15.875uH in steps of 0.125uH). The load side range
        of adjustments is binary combinations of 50pF, 100pF, 200pF, and
        390pF (50pF to 740pF in 50pF steps).

        I ran your stated impedances through the ZIZL spreadsheet calculator
        and then looked at the match with the nearest approximation the SG-
        239 could produce, with the following results:

        40 meters -- No match possible. The extremely high capacitive
        reactance value means you would need essentially a series inductor
        to match the load. The calculated Pi network from ZIZL's "T-Pi-L"
        calculator function shows you would need a 5pF output capacitor on
        the load side to match as a L network. The minimum available step
        for the SG-239 is 50pF. With this value selected, it's impossible to
        get a match within a 2:1 VSWR. Choosing a Pi network gives
        essentially the same results.

        20 meters -- This would probably work OK. I empirically determined
        the best match using available values would occur with a Pi network
        configuration having an input side capacitance of 151pF, a series L
        of 1.25uH, and a load side capacitance of 50pF. This would give a
        transmitter port load impedance of 38.7 -j0.7 with a VSWR of 1.3.
        Not coincidentally, a 59 foot piece of feedline is reasonably close
        to being a full wavelength on 20 meters, and would come close to
        repeat the actual antenna feedpoint impedance (presumably 73 +j10 or
        so in free space) at the tuner end.

        17 meters -- No match. Again, the limited choice of load side
        capacitance in the 239 has you foiled. A Pi net with a load side
        capacitance of 18pF is required.

        15 meters -- This **might** work. An L net with a load side
        capacitance of 61pF is required. This load can matched using the
        50pF output cap step with a series L of 2.125uH. This results in a
        transmitter port impedance of 105 +j1.4 with a VSWR of 2.1.
        Depending on the actual physical reality, you may get lucky here.

        10 meters -- No good again. We need a load side capacitance of 34pF;
        the minimum 50pF is way too high to work.

        It appears you have selected an unfortunate length of ladder line
        for your antenna. If possible, I would recommend changing the line
        length in small increments to see if you can get a more tractable
        set of terminal impedances. At the higher frequencies, it won't take
        much change to make a dramatic difference in the impedance presented
        to the tuner at the end of the feedline.

        The impedance values you quote look like they were derived from some
        sort of calculated model. Actual measurement of such high impedances
        in the field is essentially impossible. If this is the case, I would
        advise playing around with the modeled feedline length to see if you
        can find a compromise length that will work physically and present a
        less bizarre load to the tuner, at least on some bands. Also, as
        your experience shows, models seldom correspond to the real world.
        The fact that your tuner found matches on all bands except 15 and 12
        meters bears this out. Try pruning the feedline a little and see
        what happens. It's going to be tedious, but I think you can
        eventually find a compromise that will work better than your out-of-
        the-box installation.

        73...
        Randy, W8FN
      • QRP_1@juno.com
        Test results: The SG-239 matched to the dummy load with typical VSWR readings of
        Message 3 of 5 , Dec 3, 2007
        • 0 Attachment
          Test results: The SG-239 matched to the dummy load with typical VSWR
          readings of < 1.5:1 as measured on both the internal IC-718 SWR meter
          and the MFJ VSWR meter except for a couple of bands. Initially a
          match on the 20 meter band was attempted using the IC-718 in the AM
          mode with 40 watt carrier. The SG-239 "clicked" a few times and
          refused to match and VSWR was > 5:1.
           
          I believe I would just concentrate on getting the tuner to tune my antennas.  A 50 ohm dummy load obviously doesn't need tuner because it already has a near 1:1 match and this sometimes can confuse an autotuner.  So concentrate on what the tuner will do with an actual antenna connected before you start to worry about it tuning something that doesn't need tuned.  Also, if the radio has a built in swr bridge, use it and skip the external one to help eliminate some additional unwanted losses.

          72,
          Rick McKee, KC8AON, Ohio - www.angelfire.com/electronic2/qrp
          Monthly QRP Field Day Group - http://groups.yahoo.com/group/MQFD/
          With God all things are possible <><
        • fbparks
          Thanks to all who answered. W8FN, I really liked your description as nervous as to how the SG-239 acts sometimes. It seems that it finds a good match,
          Message 4 of 5 , Dec 3, 2007
          • 0 Attachment
            Thanks to all who answered.

            W8FN, I really liked your description as "nervous" as to how the
            SG-239 acts sometimes. It seems that it finds a good match, however
            it seems to forget where it was sometimes and tries again with poorer
            results. I guess that is why they have the "lock" feature which I
            have not been able to implement yet.

            You are correct in assuming my impedances are from computer programs.
            I used EZNEC and the ARRL program "TLW" to determine the approximate
            impedances. I was somewhat surprised to see in the December issue of
            QST in the "The Doctor is IN" column that the same two programs were
            recommended for deriving antenna impedances.

            The TLW program also includes a "tuner" program to figure the
            efficiency of different impedances which can be matched with certain
            matching networks. The Pi network used by SGC is included and the
            limitations of a 50 pF capacitor on the output end of the matching
            network can be entered into the calculation. After looking at the
            "perfect matches" such as 63' for 20 meters I choose a compromise
            match for all desired bands of operation of 59'.

            The surprising thing is matches at 80 and 40 meters, which are
            indicated to have high losses, are the most stable with the SGC-239
            with a 20 meter dipole antenna.

            Thanks again,

            Frank


            --- In Smartuners@yahoogroups.com, "w8fn1" <w8fn@...> wrote:
            >
            > Hi, Frank.
            >
            > The SG-239 (and all the other SGC tuners) works just fine feeding a
            > doublet fed with ladder line. As a matter of fact, I have one in
            > service now. I too have seen my 239 act "nervous" at times for no
            > obvious reason, but it always seems to work after a couple of tries
            > at matching.
            >
            > > Some antenna impedances presented to the SG-239 that I'm trying to
            > match:
            > >
            > > 7.2 MHz: 93 -j 1616
            > > 14.2 MHz: 88 -j 147
            > > 18.1 MHz 279 -j 646
            > > 21.4 MHz 78 +j 252
            > > 28.4 MHz 73 +j 353
            >
            > These are some extremely high impedances, and would be difficult to
            > match with most any kind of tuner. The limited choice of circuit
            > constants available on the SG-239, especially the load side
            > capacitance, makes it unlikely you will be able to match these
            > loads. Looking at the schematic of the SG-239, we can see the range
            > of adjustments of the transmitter side capacitance is binary
            > combinations of 51pF, 100pF, 200pF, 400pF, 800pF, and 1620pF (51pF
            > to 3171pF in increments of 51pF). The series L range of adjustments
            > is binary combinations of 0.125uH, 0.25uH, 0.5uH, 1uH, 2uH, 4uH, and
            > 8uH (0.125uH to 15.875uH in steps of 0.125uH). The load side range
            > of adjustments is binary combinations of 50pF, 100pF, 200pF, and
            > 390pF (50pF to 740pF in 50pF steps).
            >
            > I ran your stated impedances through the ZIZL spreadsheet calculator
            > and then looked at the match with the nearest approximation the SG-
            > 239 could produce, with the following results:
            >
            > 40 meters -- No match possible. The extremely high capacitive
            > reactance value means you would need essentially a series inductor
            > to match the load. The calculated Pi network from ZIZL's "T-Pi-L"
            > calculator function shows you would need a 5pF output capacitor on
            > the load side to match as a L network. The minimum available step
            > for the SG-239 is 50pF. With this value selected, it's impossible to
            > get a match within a 2:1 VSWR. Choosing a Pi network gives
            > essentially the same results.
            >
            > 20 meters -- This would probably work OK. I empirically determined
            > the best match using available values would occur with a Pi network
            > configuration having an input side capacitance of 151pF, a series L
            > of 1.25uH, and a load side capacitance of 50pF. This would give a
            > transmitter port load impedance of 38.7 -j0.7 with a VSWR of 1.3.
            > Not coincidentally, a 59 foot piece of feedline is reasonably close
            > to being a full wavelength on 20 meters, and would come close to
            > repeat the actual antenna feedpoint impedance (presumably 73 +j10 or
            > so in free space) at the tuner end.
            >
            > 17 meters -- No match. Again, the limited choice of load side
            > capacitance in the 239 has you foiled. A Pi net with a load side
            > capacitance of 18pF is required.
            >
            > 15 meters -- This **might** work. An L net with a load side
            > capacitance of 61pF is required. This load can matched using the
            > 50pF output cap step with a series L of 2.125uH. This results in a
            > transmitter port impedance of 105 +j1.4 with a VSWR of 2.1.
            > Depending on the actual physical reality, you may get lucky here.
            >
            > 10 meters -- No good again. We need a load side capacitance of 34pF;
            > the minimum 50pF is way too high to work.
            >
            > It appears you have selected an unfortunate length of ladder line
            > for your antenna. If possible, I would recommend changing the line
            > length in small increments to see if you can get a more tractable
            > set of terminal impedances. At the higher frequencies, it won't take
            > much change to make a dramatic difference in the impedance presented
            > to the tuner at the end of the feedline.
            >
            > The impedance values you quote look like they were derived from some
            > sort of calculated model. Actual measurement of such high impedances
            > in the field is essentially impossible. If this is the case, I would
            > advise playing around with the modeled feedline length to see if you
            > can find a compromise length that will work physically and present a
            > less bizarre load to the tuner, at least on some bands. Also, as
            > your experience shows, models seldom correspond to the real world.
            > The fact that your tuner found matches on all bands except 15 and 12
            > meters bears this out. Try pruning the feedline a little and see
            > what happens. It's going to be tedious, but I think you can
            > eventually find a compromise that will work better than your out-of-
            > the-box installation.
            >
            > 73...
            > Randy, W8FN
            >
          Your message has been successfully submitted and would be delivered to recipients shortly.