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Old 20-01-2021, 13:16   #1
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M802 Transmit Power

I am trying to get my Icom IC-M802 and wiring back in shape, having splashed the boat after seven months on the hard. The symptoms Iíve been dealing with are no power/low power on transmit based on the power bar display on the 802.

The Dynaplate is clean. The conductor to the Dynaplate is via 3 inch copper strap, and the connection between the two was sanded shiny and sprayed with Boeshield T-5. Same with the AT-140 ground/copper strap.

The house bank is charged.

The GTO-15 to backstay antenna connection is sanded shiny and sprayed with T-5.

The AT-140 antenna post is clean and sprayed with T-5. I noticed the ring connector crimp missed a few strands that had been cut roughly a year ago when I stripped the GTO-15 lead, so I cut an inch off the GTO-15 and crimped on a new ring connector.

The above got me to the point where I was seeing 4 bars on transmit, vs ĎSWRí.

I think this is the interesting part: I pulled the GTO-15 off the tuner and replaced it with 10 AWG twin lead, taped to stand off the lifeline and with the far end hoisted to just below the spreader. This temporary antenna was 50 feet long.

When I keyed the mike in FSK mode, I saw 8 bars of transmit power.

I decided (wrongly) that the GTO-15 was internally corroded, so I replaced it. Back to 4 bars!?

I donít have an SWR meter to use for test. Anyone have suggestions to isolate this?

Thanks for the help!
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Old 20-01-2021, 15:49   #2
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Re: M802 Transmit Power

There is the possibility that you hit a "non-tuning" part of the antenna where the wavelength is that which cannot be tuned well enough. Have you tried different frequencies? I am sure you did but did not mention that in your post. If everything works with the temp antenna, maybe reinstall a new antenna.
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Old 20-01-2021, 17:32   #3
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Re: M802 Transmit Power

Thanks for the suggestion... will try different frequencies tomorrow. The AT-140 end of the GTO-15 was detached to verify that there was no problem with the upper insulator. I had already verified that the lower insulator read ‘open’. I read good continuity between the lower parts of the two backstays, presumably through the bonding system. I read ‘open’ between the GTO-15 and the port backstay, meaning the top insulator is good.

I don’t understand the physics behind a failure to tune. I had attached the GTO-15 very near the bottom of the insulated backstay. The length of the insulated backstay plus the GTO-15 is supposed to be near 1/4 wavelength, right? Then the tuner adjusts the impedance for optimal performance?

If the antenna is the wrong length for the frequency, do I shorten it by sliding the attachment point up the backstay?
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Old 20-01-2021, 17:32   #4
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Re: M802 Transmit Power

Is the output consistent with the temporary antenna? I was struggling with low transmit power and went through the same troubleshooting as you report. I would occasionally get full transmit power but never consistently, regardless of frequency. A ham tested the radio on his bench for me and determined the problem was in the radio but he could not isolate it. ICOM tested the radio and isolated the issue to a board but could not isolate it to a component. I'm currently waiting for the new board to come in. Can you swap the radio into a boat with a known functioning radio?
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Old 20-01-2021, 19:50   #5
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Re: M802 Transmit Power

Read this page. Martin explains much better than I could about even and odd wavelengths, although I understand the difference and why my tuner at home will work on some frequencies while other show a higher SWR and the tuner has issues tuning.
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Old 21-01-2021, 09:02   #6
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Re: M802 Transmit Power

I have mentioned this before in another thread about troubleshooting. It is best to concentrate on one problem at a time. Don't jump around between antenna, tuner, ground, and radio. Work on one at a time until either the solution is found or time to move to the next.

As a satellite system engineer and field service guy, I follow the 4P rule for troubleshooting. The 4P's are...

Power - (is the system getting the right voltage/current to operate correctly)
Pointing - (in this case it being is the antenna pointed to the correctly satellite and correct polarization)
Parameters - (are the settings correct, i.e. when looking at the meter on the radio display, are you looking at the correct meter reading [i.e. fwd vs ref power levels])
Parts - (is the antenna working correctly, is the tuner working correctly, is the radio working correctly - this is where buckleykr points to a problem with the radio)

Just some additional hints and JMHO. Not intended to take away from what anyone else has said.
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Old 21-01-2021, 10:28   #7
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Re: M802 Transmit Power

I reconnected the backstay antenna and started doing the tests recommended by buckleykr. It looks like in most frequency bands the transmit power indicated on the control head display is 4 bars. It is not consistent— at 8 mHz 7,6,& 4 bars. At 18 mHz 6 & 4 bars. I will try to arrange with one of my neighbor boats to swap my radio in.
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