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Strange behavior - Cobra 75 WX ST

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MikeSD

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Joined
Sep 28, 2010
Messages
64
I've installed a Cobra 75 WX ST in my Jeep. Seems to work ok, but have some strange behavior I don't understand.

* I have tested it and it transmits and receives to my other CB.
* The Weather channels work fine.
* When I key it, the TX indicator goes on, and the power meter maxes to the right.
* When I unkey, the RX indicator goes on.
* Audio is heard at the receiving radio.

But here's is the problem

1) When I unkey, the LCD power indication, stays pegged as if keyed. It is definitely not transmitting though
2) if I disconnect the antenna, the LCD power level drops to zero
3) Rec data moves the received signal strength, as it should

4) The other problem, is that turning the squelch button, has almost zero effect. Only at the very counter-clockwise position, is there any background noise. I'm not familiar with this particular radio, so I don't know if there is some other explanation for the lack of background noise. Normally an AM radio will have background noise when squelch is off vs on. Mine is quiet for most of the squelch settings, for all channels.

At first I thought it might be a shorted antenna that's causing some sort of lockup but I buzzed everything out and there are no shorts, or open circuits.

This is how it's acting. It's acting like, after I key, there is some received signal that pegs the meter, in RX. The radio goes back to RX, and the signal only (no audio) is received, pegging the meter. But, like I said, it's like that. It's not exactly that. My other radio detects no RX signal. I think I'll have to see if my antenna cable is picking up some noise, that looks like RX. That might explain the lack of squelch noise, and explain why the meter stays pegged. But this is one weird problem.

Is there some condition or explanation why this is happening? Other than "it might be broken".
 
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Delta33

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Premium Subscriber
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Oct 23, 2016
Messages
326
Location
Clinton Iowa
Honestly, I wouldn't stress over it. It works, with a quirk or two so just use it. ANY repairs to it would cost more that what its worth. Its a simple, cheap cb, that's it.
 

canav844

Member
Joined
Jul 15, 2007
Messages
559
Where is the antenna in relation to the radio? And what are your SWRs and how is the Coax routed? What are you using for an antenna?

Sounds like if the problems are related, I'd bet there's a fault in the feedline (kink, wire crack, pinched by a door, faulty solder on the connector), so you're not getting much of a noise floor with nothing being recieve. This would also cause a high SWR as the signal isn't making it to the antenna (or most of the signal) and is coming back into the radio, disrupting the internal electronics.

I'm not exactly sure what you mean by "buzzed everything out" but actual SWR numbers will go a long way here. You can think everything is fine on the bench but then if a trim piece puts just a enough pressure to pinch the coax, it can make a headache for you, or if the feed wire (not the sheilding) sits loose behind solder, it may test fine move the cable and lose the conntection. Also may want to try a different antenna if you have one or someone else does and see if the noise floor changes on receive. I know within a few hundred yards high power lines are always pretty noticeable to hear with my radios, should help to give you a baseline signal generation and compare between antennas. That may help you narrow down components until you can locate the fault.

How old is the radio, do you off road? Could this be a result of road vibrations or similar?
 

MikeSD

Member
Joined
Sep 28, 2010
Messages
64
Problem solved:

First, I'm using one of those 3' Firefly antenna. Buzzing was just for shorts.

Solution: I had spare radio, antenna, jeep, etc. Nice to be able to swap out Jeeps and test. :D So I put it in my other Jeep and it worked fine. At first, I thought it might be a power issue, since one used the assessor jack and the one that worked used direct wiring to battery. But that was not the problem.

The problem was traced to a bad antenna mount connector. Not really sure why it's bad. It's not shorted. Perhaps it's open. I noticed that the center conductor barely held in the connector. I mashed the contacts together but that didn't help. Crappy connector. So, I swapped out the connector with a new one, of which I have many, and the problem went away. Likely, I had a open circuit to the antenna, which is why no background noise.

Now my radio operates as expected.

Lesson learned: Don't just plug in and expect to work. Do a proper install and test, as you go. ;)

Thanks for tips.
 
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