most common cause of transmit "squeal" ?

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treetrucker
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most common cause of transmit "squeal" ?

Post by treetrucker » Wednesday, 01 June 2016, 20:35 PM

I just joined this forum and this is my first post. i just got a new 2017 peterbilt that came with a cobra 29 LTD classic, factory installed coax with dual antennas with roof mounts. The problem is I can't transmit, every time i key the mike It puts out a loud squeal if the mike gain is turned up at all, The radio is mounted in an overhead console that used a simple velcro strap to hold it in place. There is no metal contact at the mount. what is the most likely cause of this problem ? The cab is aluminum with plastic covers where the antennas are mounted so I don't know if the mounts have a chassis ground or not.




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Re: most common cause of transmit "squeal" ?

Post by army1975 » Wednesday, 01 June 2016, 21:36 PM

well, might be the mic is too close to the radio. I have my mic gain at the 2 o'clock position on the radio and if I move my mike close to the radio, it will squeal. luv that talkback. lets one know what is going on with transmitting. my mic is the Astatic 636L Stars and Stripes. hope this helps. good luck.


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Re: most common cause of transmit "squeal" ?

Post by TrblShooter » Thursday, 02 June 2016, 10:52 AM

treetrucker wrote:I just joined this forum and this is my first post. i just got a new 2017 peterbilt that came with a cobra 29 LTD classic, factory installed coax with dual antennas with roof mounts. The problem is I can't transmit, every time i key the mike It puts out a loud squeal if the mike gain is turned up at all, The radio is mounted in an overhead console that used a simple velcro strap to hold it in place. There is no metal contact at the mount. what is the most likely cause of this problem ? The cab is aluminum with plastic covers where the antennas are mounted so I don't know if the mounts have a chassis ground or not.

What kind of mic are you running with the radio, the stock mic or a power mic?



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Re: most common cause of transmit "squeal" ?

Post by MDYoungblood » Thursday, 02 June 2016, 11:07 AM

Hello treetrucker,
Welcome to the forum. To understand a little better you hear a squeal thru the speaker every time you key up? Have you tried anther mic to see if that cures the problem, if it doesn't then we'll get into troubleshooting.
As a member to the forum could you post a intro in the "Welcome to the Forum" topic here, viewforum.php?f=89" onclick="window.open(this.href);return false; , so others can say "Hi", thanks.

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Re: most common cause of transmit "squeal" ?

Post by treetrucker » Friday, 03 June 2016, 22:12 PM

Yes I hear the squeal through the radio's external speaker and so does anyone else that I'm trying to talk to. i'm using the stock Cobra mike that came with the radio and yes I've tried 4 or 5 other mikes and they all gave the same results , SQUEAL !! One more detail to this , we had a local Radio "tech" that our company uses to install and set up our Motorola company radios supposedly set the SWR on my radio but he left it like this ! And My truck is one of 3 that went into service at the same time and all 3 have had trouble with their CB radioos. one of them was fixed with a new mike and I'm not sure what the other needed to fix it. Between the time of my original post and now I put in a new radio, unopened out of the box and it works just like it should, great. Also the problem radio put out a lot of electrical noise that seemed engine or wiring related, where the noise would go up + down in relation to the engines rpms. and this new radio has none of this. Since this 1st radio is new I'd like to fix it so our company can use it as needed.




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Re: most common cause of transmit "squeal" ?

Post by sonoma » Saturday, 04 June 2016, 4:49 AM

did the tech put talkback in the radio? it may be too loud if he did and with a stock mic it will pick up the rf from the radio. have you tried it with out talk back? after a peak and tune if it has talk back it will do this if you are using a stock mic. also an external speaker can cause squeal if it is too close to the radio with the extra wiring from the speaker coiled up with the radio.. so many things can cause this and not enough info here to give you a real good answer.



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Re: most common cause of transmit "squeal" ?

Post by MDYoungblood » Saturday, 04 June 2016, 8:20 AM

Wonder if the speaker is one with talkback. After the radio change and the new one works, hook the old one up on a bench and test it out, if it's still squealing then it's time to open it up to see whats causing this or since it's a new radio send it to Cobra for the factory warranty or back to the Peterbilt dealer for replacement, it is a new truck and for the cost of it the radio should be covered.

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