New Cobra 29LTD sticks in TX only with a mobile antenna

[Moleculo]

I have a new Cobra 29LTD with a strange problem - The radio sticks in Transmit but only when it's in a vehicle with a mobile antenna. If you use it on the base, it doesn't stick. It almost seems like an RFI problem. I did find that Cobra has a TSB about this issue, but no resolution. Does anyone know how to resolve this?

http://www.cbtricks.com/radios/cobra/service_bulletins/graphics/tsb_10008.pdf

 

[Beetle]

Does sound like RF in the shack, or in the vehicle anyway. I'd put a choke in the positive power lead as close to the radio as possible just to see what happens.

Stock radio? No modifications at all? No amplifier? Coax and connectors absolutely ok?

Since according to the topic title, it "sticks in TX", maybe you could move to OK, NM or LA? (sorry... )

(From that link, it sounds like Cobra is pretty clueless, too.)

 

[Robb]

I'd agree withe Beetle, as far as the RF in the vehicle.

Since most modern day CB's no longer use a relay to kick the TX circuit on, they have gone to a diode switching circuit - instead. Something in that circuit doesn't' respond well to excessive RF - obviously. The Cobra bulletin also pointed out that grounding was another feature to this problem. Between these two diagnoses -and the RF sensitive circuit- one must conclude a bad ground in this circuit. Perhaps due tho the soundtracker circuit - since earlier 29LTD didn't have such - nor this problem.

I'm no tech; but that is what makes sense to me...