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N1OOQ
Mon 26th Dec 2016, 21:36
So I bought an Omni D about a month ago. Just now getting it up on the air. I'm using an 80m dipole, fed with ladder line, from a (brand new) MFJ tuner. Everything great, except... after being on for maybe 1/2 hour to 1 hour, the radio just sort of goes deaf, and at the same time, it will barely transmit anymore. By deaf, I mean the noise level drops way down. You can still hear stations, just weaker. And you need to crank the "drive" knob all the way over to get anything at all out of the transmitter, after having it set at maybe 1/3 for normal SSB, where it just lights the ALC lamp on voice peaks. If I turn it off and come back an hour later, everything is back to normal.
A couple of details: I haven't bothered trying to get a good RF ground. Shack is on the 2nd floor. I can indeed feel a minor sting on the chassis at some freqs. Are these radios super sensitive to that? I scoped the CW output waveform - nice and symmetrical, so I don't think the finals are blown or anything like that.
My first guess would be something getting hot and going out of spec, and then coming back when it cools off... any guesses? -N1OOQ

N1OOQ
Tue 27th Dec 2016, 17:42
I hooked up the radio to a dummy load and the scope, and dumped about 20W at 80m into it for about 15 minutes. At that time, the output started going unstable in amplitude, and then dropped down to almost zero over a few seconds.
Checked the output from the (TenTec 252MO) power supply - still a nice clean 13.3V.
Cranked the drive knob all the way over - yup, this is my exact problem - I get a little bit out with drive all the way up, but that's it.
So at least I can duplicate it off the air.
-N1OOQ

N1OOQ
Wed 28th Dec 2016, 11:50
Last night I turned the radio on and let it sit for a couple of hours. The problem returned. So it's not tied to transmitting, just to warming up in general.
Any Omni D experts out there? -N1OOQ