Mysterious feedback squeal that doesn't make a lot of sense...

By any chance it is one of those 'talkback speakers'? Easily identifiable by a knob on the side of the speaker and having two leads to plug into the radio- one into external speaker and the other into the PA jack.

Is the speaker cable running close to the coax antenna cable? If so then try re-routing it.

Another possibility is that the speaker is too close to the radio. It might be picking up stray RF from the General Lee or Connex and feeding back. This would be my guess.

Try relocating the external speaker- it should be up near your head anyhow because that's where your ears are.

 

If TB is off and you hear it in the transmitted signal the speaker is not the cause. I would look at SWR and the quality of ground in your antenna system. Especially since two export class radios are showing the same symptom. Unless of course the same shop put the same bad idea of diode swing mods in both, which would make both radios highly unstable and more sensitive to RF into the audio feedback issues. You can have only a slight ground or SWR issue where diode modded export radios have this problem yet the same models without these swing mods do not since they have greater stability.

 

I stopped mine from squealing by wrapping the excess wire lead around the speaker several times. My speaker sits right behind the radio on the dash.

 

Your concept seems to make sense Outlaw. I tried a completely different external speaker today, held it 4-5 feet away from the radio and still has the same exact symptoms. I did check SWR with an external meter, and it's within spec (little high at 2...) I'll look at a good ground next. This older truck is much better than most newer ones for ground, but a door hinge never made a very good one at any time I understand. I also just though about the radio itself may not have a really good ground to the body. I should run one for the radio, a separate one from the antenna down to chassis and see if that makes a difference.

Thanks for the feedback, no pun intended....

 

If someone else hasn't mentioned it, check to see that any grounds you have aren't close multiples of 9', 18', 36' (excessively long). This also can have an affect in which grounds become "resonant" and act like antennas for RF to travel along and get into things you don't want it getting into. (speakers, causing mikes to 'bite' your lip.....stuff like that) With the newer "plastic" trucks (figure of speech), grounds are harder to install, or difficult to find places TO ground. Something so simple, and often not thought of, can cause lots of trouble. Whatever grounds you have, make sure they are "odd" multiples of the above so that can't happen.

I once had a car that had mysterious motor noise that I could NOT, for the life of me find why! I tried EVERYTHING---including pulling my hair out! One day I was driving and stopped at a light and the noise STOPPED. When I released the brake, the static returned. WHAT TH.............??????????? Press the brake, noise gone. Don't know why I hadn't noticed this before, but maybe I was onto something.

I removed the tail light lens and screwed out the bulbs with the engine running. Noise STOPPED. ??????????? Anyway, in sniffing out this curious problem, I found that the noise was traveling over the wiring harness and antenna cable TO the antenna, and returning to the HF receiver. The stoplight bulbs were acting as little antennas to radiate this static. Recognizing this, I knew I couldn't really change the car's wiring harness, but I COULD stop the noise. I got some hardware screen door wire and fashioned little "grids" that fit inside the red lens cover and then screwed to the metal body of the car. This acted like a grounded barrier (grounded grid circuit? ) thru which RF could NOT radiate to the nearby antennas on the deck and bumper! Problem solved!!!!

This story may not apply to YOUR situation, but the suggestions made may, and it illustrates that dealing with RF and grounds often have creative solutions! Good luck!

GF