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have the following set up: flex6500 but not using built in atu; 20 ft flagpole antenna, ldg rt 100 at base of antenna; about 25 ft of buryflex coax buried in pvc in ground; in shack- rc 100 controller; have ferrites on dc cable to radio and one on coax from 6500 to rc 100 controller

so the idea is that the dc signals travel from the rc 100 controller to the tuner etc. the problem is that rarely can a decent <1.7 swr be obtained and if the swr is < 1.7 it is not reliably maintained ie. not kept thru one more that one ft8 cycle with the next cycle anywhere from 9 to 3 swr; usually run 20 watts rf; did the ldg hang up correction numerous times and can't fix the problem

would appreciate any input to help diagnose this situation

Thanks Greg K4GAZ


  • Bob K8RC
    Bob K8RC Member ✭✭✭

    Sounds like the tuner is in automatic and not finding a match. Each time you transmit it tries again and is at a different mismatch at the end of the FT8 cycle.

    You don't say what band you're on but your antenna is electrically short on some of them. Try transmitting FT8 (call CQ) on 10m through several cycles. If that works OK then try 12m if that's OK go to 15m and so on. If it works OK on some frequencies but fails on others then your antenna impedance is getting out of range of the tuner.

    If it doesn't work anywhere then you might have an RF arc happening somewhere. That will also make automatic tuners freak out.

    Good luck.

  • Ken - VE5KC
    Ken - VE5KC Member ✭✭
    Are you you using a LDG RU-4:1 Unun or similar between the tuner and Antenna? You notice it has a SO-239 for connecting the antenna? Not what you would expect on a tuner for a long wire or vertical antenna. It needs a Unun between the tuner and the antenna. This is really a repackaged version of a LDG tuner that goes next to the radio, inside.

    I just returned a RT-100. They seen to work for some but I didn't get a descent match on any band even using it with the LDG RU-4:1 Unun. I was able to get good matches using a LDG Z11 Pro at the radio with the RU-4:1 Unun at the coax end, feeding the antenna. Not necessary where you want the tuner but the radio was happy.

    In the end I replaced the RT-100 with an Icom AH-4 auto tuner. Unfortunately this setup is not fully automatic (at this time). To use with a non Icom radio, you need to make a simple control box with a button to start it tuning. On the positive side, this tuner was designed to be used with short whips, vertical and long wire antennas. It gives me a good match on 80 - 6 meters with a 27 ft. vertical, 10 ft. off the ground.

    73.. Ken - VE5KC
  • John KB4DU
    John KB4DU Member ✭✭✭✭

    How long has the coax been inside the pvc? This can be a tough environment for coax. As noted above, 29 feet is pretty short. Connecting an antenna analyzer to the antenna base might give a clue.

  • Salty Z
    Salty Z Member ✭✭

    Thanks for all the suggestions. will try these out and see if anything works.

    Greg K4GAZ

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