Tuesday, November 29, 2011

A long-standing RF feedback problem solved

For a long time now my Yaesu FT-1000MP has been suffering from a problem where the radio does an automatic factory reset when I am on 10 metres (28 Mhz). This doesn't happen every time. Sometimes I can run 100 watts for ages without a problem. At other times, the radio resets once I go above 80 watts.

So I spoke to a couple of ham friends about the problem, determined to fix it. It seemed that some RF was getting back into the radio somehow and that this was causing the CPU to reset. It was only happening on 10 metres. One time I mistakenly called CQ on my Icom 746 through the Antron 99 with the FT-1000MP switched on and the MP reset!! The problem was a puzzle for me, but clearly it was related to RF feedback or a problem we hams know as "RF in the shack".

One ham friend said that as 10 metres was the shortest wavelength, it was highly likely that at least one of the cables running into the radio was of such a length that it was picking up RF from a harmonic of 28Mhz and feeding it back into the radio.

So I set about transmitting on 10 metres with various cables removed, or choked. Obviously the AC cord cannot be disconnected, so I choked it with a couple of ferrite beads. No improvement. I disconnected the coax from the Butternut vertical which feeds into antenna socket B (I was using the MA5B minibeam on socket A to transmit). No improvement. The radio was still resetting.

The I disconnected the earth wire from the back of the radio. I have a station ground, a copper rod, sunk into the ground just outside the shack. Disconnecting the ground wire did not make any difference. The radio was still resetting.

At this stage I decided to try to disconnect leads that were running into the front of the radio. I plugged out the desk mic and keyed up on CW. Radio still reset. I disconnected the lead from my Signalink USB. Still resetting.

There was only one cable running into the radio which I hadn't tried. And that was the cable running from my Kent morse paddle into the CW Key socket on the front of the radio. So I disconnected that and keyed up on 100 watts in FM and . . . . . . no reset!!!

I started to get excited. I powered up the Acom 1000 linear and decided to put more power out to see if the radio would reset. I plugged in a homebrew CW paddle which has a much shorter lead and keyed up in CW. No reset. I put the power up to 400 watts. Still no reset!! Oh boy was I happy.

Given that it was Sunday and the CQWW CW contest was on and Irish hams are now allowed to run 1.5kW in contests I decided to put out even more power. I managed 1 kW without a reset.

The solution, given that the Kent key cable seemed to be causing the issue, was to shorten the cable to the same length as the homebrew paddle. A couple of snips with wire cutters and a bit of soldering later, problem solved!! I was able to run 600 watts on 10 metres Sunday evening without any problem.

Hopefully this might provide some assistance to anyone who may be experiencing a similar problem.

I have to put ferrite beads on the cables running into my laptop. Certain peripheral devices, such as the external keyboard, mouse etc, are malfunctioning because of RF in the shack. I will let you know how that goes when I acquire some ferrites in the coming week.


  1. Thanks for the info Anthony. I am really happy you got it resolved. Mike M0SAZ

  2. Good morning Anthony, very good diagnosis of the problem and narrowing it down. It sure can take some time to get close and the try this and try that method has worked for me as well. I have had my share of RF in the shack. I too have to put ferrite bead on the keyboard mouse as I had some funky things go on with the PC. My wife Julie's Mac desktop was having it's screen scatter all over the place with a little as 3 watts from my K3. It turned out the Mac mouse is very good at picking up RF. So the only solution there was to replace the mouse. Great to hear you have solved the problem.

  3. It's always a struggle to find RF problems Anthony. Glad you find the solution. I think it's the best to have all cables as short as possible.
    73, Bas

  4. Thanks indeed Mike. I was beginning to think it was a problem with the radio. Because 10m wasn't open in 2009 or last year it wasn't really a problem. But this year with 10 open so good I am afraid to put out any more than 70 watts in case the radio resets. Now I can relax and run more power if needed. It's great to get it solved.

  5. Mike and Bas, thanks for the comments. I am getting, this weekend, a little bucket of ferrite beads from a ham friend. I will put them on all cables running into both the laptop and the MP. It's well worth doing.

    My problem is that my beam is pretty much over my head in the shack. It is attached to a pole bracketed to the outside wall of my shack (just the other side of the wall where my EI2KC number plate is!) Also the hot legs of my inverted Vs are only about 10 or 15 feet from the shack. So RF in the shack has been an issue for me for a long time.

    Hopefully now I will get it all sorted out.


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