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PGXL RFI suspect

Hi all,

I've moved somethings around and suddenly I've noticed the amp errors out on 40m do to high swr.

The antenna path is: Flex6600 to PGXL port A, Port A output to Palstar HFAUTO input, Ant 1 on Palstar though about 75 feet of LMR 400 to 2.4 to 1 Balun Designs Balun to 80m loop antenna suspended between the trees.

So I've done the following:

1) PGXL in standby: Tune Flex600 - HF Auto tunes to 1.2:1. Watch SWR as I increase power. No issues all the way to 100w.

2) PGXL online: Tune Flex6600 from 2 watts up to about 40w. Somewhere around 30w the PGXL will display HI SWR FIRM and drop out. The SWR rises. HOWEVER the Palstar still shows SWR of 1.2:1 during this process. This is intermittent and just now I tried it and it worked as expected.

3) PGXL direct into MFJ dummy load. Operation is as expected. No rise in SWR as power is increated.

4) PGXL through HF Auto tuner into MFJ dummy load. Operation as expected. The tuner first tuned the dummy load to 1:1 then power increase kept the SWR there. Bypass was the same. 1:1 and as much power as I wanted with no issue.

5) on 20m. PGXL through HF Auto, antenna tuned to 1:1.04. I can run as much power as desired and PGXL is happy.

When the issue occurs I do hear a buzz in my speakers. So I highly suspect RFI and I wonder if RFI is getting into the net cable causing the PGXL to freak out.

Anyway will keep looking. Wonder if anyone has seen this behavior before.

Mark WS7M


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Mark, I have seen similar things over the years. Sometimes it is coming in on something completely non-ham related. I usually start by unplugging everything in the shack not related to the rig, amp or tuner (and these days, the network). To rule out the network, you might want to connect your computer directly to your 6600 to see what that does.

    Try unplugging the speakers to see if they are the conduit for the RF getting in. If that is it, some ferrites on the speaker and power leads should do the trick.

    Item #2 being intermittent may be indicative of a loose connection. If you haven't already, check all coax and ground connections. I usually completely disconnect and reconnect them to get past any possible corrosion issues (not that we have much of a prob here in CO with that...). Sometimes you get a ground loop, and the solution is to un-ground some piece of equipment that is currently connected to ground. This can be particularly difficult to find, but often pays big dividends.

    You might also try ferrites on power and signal cables. It can even be cables to an unused radio or other equipment routing RF back in to where it does not belong.

    Last thing I can think of - try taking the 4:1 balun out of the circuit to see what, if any, effect that might have. The balun SHOULD help keep RF off the outside of the cable, but who knows?

  • Mark_WS7M
    Mark_WS7M Member ✭✭✭

    Hi Len,

    Yes the search begins. RF is so strange. I had the radio and amp in a back room, LOTS more coax, not a problem. Moved it to the shed where it is probably 25 feet less coax to run through and suddenly a problem.

    I am probably going to start with the speaker, key, and LAN cables with cores and see if I see a difference.

    Then I will go the route of disconnecting everything.

    Congrats on your Super Elmer my friend! You deserve it.

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Thanks Mark, I appreciate it!

  • Richard Everett
    Richard Everett Member ✭✭

    I have the exact same problem. I suspected RFI as being the culprit to the problem also and after reading this I now have a path to follow in order to get use of the PGXL to where it should be in my setup. I have hated RFI from day one of becoming a ham radio operator and my battle to put an end to RFI starts a new chapter with my purchase of the Flex PGXL. SIGH

  • Mark_WS7M
    Mark_WS7M Member ✭✭✭

    Hi Richard,

    Yes RFI is a hassle but RF is a strange beast to begin with.

    While I think there is some "science" behind this belief, but much of my RFI disappeared when I changed to an 80m loop wire antenna. Prior to that I had been using an EF HW antenna which are known to have high current nodes especially near the feed point.

    In contrast my 80 loop, once in the "sweet spot" has few high current nodes, at least that is what the simulation software says and they are no where near the feed point.

    It feels to me like this 80 loop is like a magnet that attracts RF and radiates it rather than sort of fighting you. I can switch quickly to a simple 20m wire vertical and the result is RFI tends to be worse.

    So my point is simply that to solve RFI I suggest the following sequence:

    1) Make sure single point ground. Follow the suggested techniques to avoid ground loops

    2) Tune your antenna to be the best it can be without a tuner. Investing in a RigExpert or similar tool is key. Don't rely on a tuner to do this job for you. The antenna should be as resonant as possible.

    3) Disconnect everything except the bare minimum stuff needed to run the radio.

    4) Now run in the exact configuration you expect to get RFI in. Start to add back in connections until the RFI appears. Choke that line and repeat.

    Keep the confidence up! You can solve this.

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