Question about Cobra 148 GTL 120-Channels Base CB Radio
I installed a EB-1 Astatic echo board in a Cobra 29 LTD Classic.Now anytime I key the mic I get a hum in the talkback.It will stop if I grab the mic cord or turn the mic gain down to zero.I am using a RK56 mic and have installed the board correctly.I can knock alot of the hum down by turning the power down on the radio .I have tried different values of talk back res.,but it does not help.
Have a 29wxnwst cobra. Installing astatic echo board. What is J1 and J2 on echo board
Posted on Dec 26, 2009
This is a classic indication of a lost shield or ground connection in the mic circuitry. Double check these connections for good contact in the mic *and* the plug at the other end of the cable.
Check the grounding and SWR or "match"of the antenna system, too. A poor SWR (greater than 1.5:1 or 2.0:1) can cause the reflection of RF back to the radio. Modifications can increase sensitivity of the mic to this unwanted RF.
Posted on Sep 29, 2009
Testimonial: "thank you,looks like that fixed it,high SWR"
I had the sane problem. Solved it by adding a 1k resistor into the audio wire going from the mic connector to the echo board. A better way is with a choke, 5uH to about 15u, but I didn't have one at the time.
Posted on Feb 26, 2010
Also try a 100 ohm 1 watt resistor for your talkback
Posted on Nov 11, 2009
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Posted on Jan 02, 2017
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