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Cobra 29LX Antenna Warning
- Thread starter Realred
- Start date
That is one of several Cobra radios that have a known issue with the AWI, where it lights up even if there is nothing wrong with the antenna system. It would seem that the 29LX model does disable transmit when the AWI is activated. The fix may be as simple as adjusting the correct VR in the radio, or it may be much more complex. Hopefully one of the resident WWDX techs will enter the chat.........
Thanks, I have tried adjusting VR6 as per Cobra's instructions but it has no effect.
I looked at the schematic on cbtricks for the 29LX LE and that antenna circuit has me scratching my head. I think they ran into issues, tried something else, then gave up.
TR19, which looks like it was an inverter driving the ANT signal wire via R83 at one point, is now doing nothing.
R81 says NA, which I assume means it isn't there. Makes sense too. The schematic shows that going to the collector of the 10.24MHz oscillator. Pulling that line up during high SWR makes no sense. It would have to be pulled down to kill the oscillator supply. Not what I thought R81 was for, see next post.
Then they have a dotted line called "jump wire" bypassing TR24 altogether. Not sure if yours has that wire, but it seems they tinkered with the idea of using the diode detector voltage directly on the ANT alarm wire.
Does yours jumper TR24? Am I even on the right schematic lol?
I wonder if a diode went bad and/or something happened to the ANT alarm MCU input (or is that just an LED off the ANT wire?).
My guess is that they tried to use TR24 and TR19 as a comparator/driver for the LED and it didn't work as planned.
TR19, which looks like it was an inverter driving the ANT signal wire via R83 at one point, is now doing nothing.
Then they have a dotted line called "jump wire" bypassing TR24 altogether. Not sure if yours has that wire, but it seems they tinkered with the idea of using the diode detector voltage directly on the ANT alarm wire.
Does yours jumper TR24? Am I even on the right schematic lol?
I wonder if a diode went bad and/or something happened to the ANT alarm MCU input (or is that just an LED off the ANT wire?).
My guess is that they tried to use TR24 and TR19 as a comparator/driver for the LED and it didn't work as planned.
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I don't think R81 and that trace over to the oscillator collector was ever intended to kill the oscillator.
I think it was just the top half of the VR6 divider and used to set the emitter voltage (the comparator thing). I bet that once the base of TR24 started to climb due to reflected power, the increase in current through VR6 fought it. Emitter would have went up too unless R82 were huge and the gain of TR19 high compared to the divider below
I think it was just the top half of the VR6 divider and used to set the emitter voltage (the comparator thing). I bet that once the base of TR24 started to climb due to reflected power, the increase in current through VR6 fought it. Emitter would have went up too unless R82 were huge and the gain of TR19 high compared to the divider below
I appreciate the analysis Brandon. I don't have a jumper in the vicinity. I just broke vr6 pulling it out to test. I'll find something to replace it with and start poking around. TR19 and TR24 test good. This radio has the lcd screen not just a light. I'm wondering if I have a bad chip on the display board have no idea how to check.
If you are sure its not a real swr problem, i would be tempted to short across C450 (the electrolytic at the base of TR24). That would hold its base low regardless of what that 10k is feeding it. If the warning goes away, its an issue around the directional coupler and diodes. If the warning does not go away, its further down the digital path.