M802/AT140 and occasional high SWR

[fairbank56]

You mean like this? Iv'e done a few like that. It works quite well and is a lot sturdier than it looks and you can certainly see for sure if you have a shield connection problem

You might want to take the cover off the tuner and check the circuit board to antenna insulator connection. Seen a few of those get loose. Also check the ground stud connection, seen those loose as well. Be careful of losing the small nuts behind each cover screw. Yet another downfall of these tuners not to mention that internal RF ground connection. Those nuts are recessed inside nut shaped holes. Pain in the butt. I'll take an SEA or SGC tuner over these junkie things any day, and they do work with any radio.

Eric

[jonturgeon]

Yup, that is how I did it. Seemed easier to make sure I had a good connection. On the topic of the SGC tuner. I thought of getting one of those a couple of years ago to use with the 802. What stopped me was my limited understanding as to how the Icom control cable would connect (or even if it would need to connect).

[Auspicious]

Originally Posted by jonturgeon

The odd thing I am seeing is when I transmit all seems good and low SWR, then several seconds into the transmission, I get high SWR, at that point I continue to hold the mike button down but stop talking. The radio continues to transmit with high SWR like I am still talking. If I re-tune then all is ok. Can someone explain what is happening?

Not sure what is happening. Perhaps some background will help. When you hold the mic button down but don't speak power drops to nearly nothing. Single sideband, as a mode, only transmits when there there is audio so when you stop talking and assuming no meaningful background noise the power output drops, almost certainly below the point that would allow the tuner to tune.

Still could be a tuner fault but again most likely a bad RF connection.

Originally Posted by jonturgeon

One more addition, I do have the T-4 installed right before the AT140.

Then don't worry about ferrites on the coax.

Originally Posted by jonturgeon

On the topic of the SGC tuner. I thought of getting one of those a couple of years ago to use with the 802. What stopped me was my limited understanding as to how the Icom control cable would connect (or even if it would need to connect).

You don't need the tuner control cable between an 802 and an SGC 230. Just hook up the RF cable between the radio and the tuner and run power to the tuner. Done. Works.

[jonturgeon]

Thanks for the SGC info. Wish I would have gotten that one when I bought another AT140 to try and resolve this issue (about 2 years ago, this has been off and on for years now). I just temporarily replace the coax run with a pre-made coax that I keep as a spare. Same problem with SWR so I think I rule out a coax issue. As it sits right now I can talk ok (most of the time, sometimes high swr) but when I whistle into the mike it will 1. in short whistle bursts be ok, with a several second whistle at the end of the whistle high swr until I release the mike. I also have a Pactor modem and this will on occasion have high SWR after tuning.

[Auspicious]

Well darn -- two coax runs and two tuners and same issue. I'll noodle on it. Maybe Eric or Bill has an idea.

[btrayfors]

Bound to be a bad connection somewhere. Something too loose, having surface corrosion, an internal break in the wiring, water intrusion, etc.

Pay very careful attention to the connectors for the control cable. They are junk....totally unsuited for a marine environment, but Icom has chosen to use them anyway. Those little pins tend to go astray, get bent, get corroded, come loose or come out easily.

I agree that one would not think first of the control cable, given the symptoms first described (intermittent SWR), but I suppose the tuner could somehow be attempting to retune while transmitting. Anyway, rule that one out.

Next, I'd put a good power/SWR meter in line near the transceiver box. And replace the antenna coax at the back of the radio with a dummy load. Use the low or mid power setting first, the FSK mode, and press the mic button. Leave it depressed for several seconds and see what power output you get.

Then, kick up the output to high power (Func High). Repeat the process and see what you get. You should see a steady output...no wavering and certainly no flashing "SWR" indicator. This assumes that the two pigtails are properly terminated with PL-259 connectors....no shorts or opens.

Now, replace the dummy load with the coax-to-tuner connection. Try the output power/swr tests again, picking a clear frequency.

If you get the intermittent SWR problem now, and didn't get it with the dummy load, then you have a problem somewhere in the antenna system, meaning coax and the control cable to the tuner, the tuner itself, the RF ground system, the GTO-15 wire to the antenna, or the antenna itself.

Some detective work should find the problem.

Sometimes coax goes bad with age, mistreatment, misuse, and just plain use....especially when it hasn't been terminated correctly and protected from water and moisture intrusion in the first place.

If you suspect the coax, replace it and be sure the connectors are put on correctly. If the run to the tuner is very difficult, use a longer length of NEW coax....hey--it's not that expensive --... and run it thru the cabin and cockpit to the tuner to see if that fixes the problem.

Good luck, and please let us know what you find.

Bill
WA6CCA

[Auspicious]

Originally Posted by btrayfors

Bound to be a bad connection somewhere. Something too loose, having surface corrosion, an internal break in the wiring, water intrusion, etc.

...

So we're back to post #8. *grin*

Actually Bill's words made me think of another possibility. The word is "system." It may be that a backstay insulator is failing. I'm really shotgunning here. If the step's Bill outlined indicate an antenna system problem you can try hauling some wire up on a spare halyard instead of using the backstay. Since the problem has continued through two tuners and two pieces of coax the problem should be somewhere that has been consistent through those equipment swaps.

[jonturgeon]

Although a bit old thread I thought I would follow up since I am back in good internet coverage. The end result of all this was that I bought a new M802 and it fixed the problem. After many attempts with Icom support telling me it was an installation issue and after them physically testing the radio the new one works just as it should (what a joy). I am pretty sure this issue was with this radio from day 1 (about 10 years of banging my head, I guess I am slow learner ;-) ) It finally took an independent radio guy to come by the boat and redo all the tests I had already done to convince me it was the radio. Oh, once Icom support admitted the radio was not working properly they informed me they could not fix (could not even tell me what was wrong with it other than it did not work).