Originally Posted by jonturgeon
Hello, sorry this seems to have been discussed a lot but I am not sure it is the same issue. Our M802/AT140 will tune correctly and work
perfectly some of the time. Next time it will not tune (though the indicator on the LCD says "TUNE") and will have high SWR and cutout on transmission
. Odd thing is usually the first few seconds of transmit are fine. Almost like it loses the tune.
Sorry for your troubles.
The 802 doesn't have an SWR meter per se. The foldback circuitry in the final stages of the radio
(which protects the solid state amplifier from cooking
itself when faced with a significant impedance mismatch) lights up the SWR indicator as part of power reduction.
Losing tune is possible but unlikely. It sounds like you have taken the right steps. Lets go through them again.
The most likely cause is a loose connection. Just about everything heats up, at least a little with use. The scenario you describe is classic
loose or intermittent connection.
Lets do the easy stuff first. Disassemble the backstay connection (is that what you have), clean it, and put it back together. If a hose clamp is involved that needs to be fixed. Get back to me and I'll send you pictures of the best way I have found for that connection. If you don't have properly crimped and shrunk ring terminals that should be addressed.
is, at a minimum, scrubbing the connections with a pencil eraser.
at the antenna and ground terminals of the antenna tuner.
The most likely cause of what you are seeing is the coax between the radio
and the tuner. It may be a loose connection or corrosion
in one (usually at the tuner) but it is very possible you have a badly terminated connector. If fishing
new cable isn't too hard you'll often solve the problem most efficiently by pulling new, quality cable (8X, 213, or LMR-400) with professionally terminated connectors. If you can't pull a cable with connectors attached you really want some help putting on the connectors. The crimp type are not great. Silver-teflon is what I use. Let me know where you are and I'll help you track down someone that can help. Hams that maintain repeaters are a great resource.
You say that you replaced the control cable connector at the tuner. Did you do that yourself? How? Crimp or solder? Are you shore you got the pin-outs correct? Can you pull out the cable and ring out the pins to make sure?
Make sure everything is properly terminated.
Explore changing the coax.
Then come back. There are second order factors we can start looking at after that like ground loops but those are much less likely than a bad connection.
Where are you?