Question about Cobra 148 GTL 120-Channels Base CB Radio

4 Answers

Feedback problems with astatic echo boards

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.

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Have a 29wxnwst cobra. Installing astatic echo board. What is J1 and J2 on echo board

Posted on Dec 26, 2009

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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"

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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

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Also try a 100 ohm 1 watt resistor for your talkback

Posted on Nov 11, 2009

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Documentation Project
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Mic Wiring
Stock
1- Shield
2- Audio
3- Transmit
4- Receive
Astatic (4 wire)
1- Shield
2- White
3- Red
4- Black

Astatic (6 wire)
1- Shield & Blue
2- White
3- Red
4- Black
Yellow NC
Daiwa EM-500
Cobra CA Series

1- Shield & Black
2- Red
3- White
4- Blue
Galaxy DC-521S (4 wire)
1- Shield
2- Yellow
3- Red
4- Black
Galaxy CB-660EI
1- Shield & Black
2- White
3- Red
4- Blue
Sadelta
1- Shield
2- White
3- Brown
4- Green
Turner
1- Shield & Red
2- White
3- Blue
4- Black
Yellow NC

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1 Answer

Installing an Astatic Echo Board in a Cobra 148


There should have been instructions that came with your reverb board. You are going to need to drill another hole in the case of the radio, or find a control where you can install a dual control knob onto.

Your reverb board is likely going to need 8v, so you will need to locate that off the logic board, likely from the frequency synthesizer. The the audio lines from the mic, or the output of mic amp, are going to be redirected to the reverb, and the output of the reverb feed back to where the wires were removed from.

If I recall correctly, the 148 is a bit of a bear to work with, not much room inside. You will likely have to get creative in placement of the reverb board itself. Make sure to wrap well so that it doesn't get tossed around and break something inside.

Sep 15, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

Looking to install astatic echo board in uniden PC78XL


usally on most radios you will unplug the wire that comes from the number two mic plug. you will hook you sheid witch is the 2 little black wires from the echo board to number one mic plug. then the two wires will go to wire you unplug and the other one will go to number 2 mic plug.

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Goodluck
Rob

Nov 02, 2008 | Astatic 636L Noise Canceling Microphone...

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