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Message |
    
Koolaid41514
New member
Username: Koolaid41514
Post Number: 1
Registered: 1-2009
| | Posted on Sunday, January 04, 2009 - 8:38 pm: | 
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Hi all,
I have 2 Cobra 200 GTL DX mobiles. Lately, both of the units have had an intermittent RX audio problem when installed (one at a time) in my 2008 Mack Granite dump truck.
The problem I'm encountering is that the radio will receive at a normal level (while moving or stationary) and occasionally the radio's Rx audio will mute. You have to momentarily key the mic to get the audio back up. The strange thing is that both radios have the same symptoms. One is a 1st generation 200 and the other is a 4th geration 200 (last production run).
Friday, I disassembled my antenna system (102" whip) and checked the grounds, cleaned all connections, and checked feedline with an MFJ 269 analyzer and dummy load.
Any suggestions????? |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2724
Registered: 1-2005
| | Posted on Thursday, January 08, 2009 - 2:52 pm: |
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Since both radios are acting up in the same way I would suspect a problem with the install. Installation gets much more complicated with these higher power radios.
First thing you should look at is the antenna placement.
You need to have as much of the 102 inch whip above the truck as possible.
You want it mounted to something that is a good solid ground to the truck body, not to just like a mirror bracket.
You should be using a stud mount with lug connected coax. If not I highly recommend getting one.
Good quality coax! You checked the coax using your MFJ 269 but you say this is an intermittent problem. Try some fresh coax, mini 8 at least.
If installed right the 102 inch whip is foolproof. Check that off and try some new coax.
Any details you can provide is very helpful for us to help you.
Good luck!
Kenny
CEF491
Reading the mail around Indianapolis Indiana!
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Koolaid41514
New member
Username: Koolaid41514
Post Number: 2
Registered: 1-2009
| | Posted on Sunday, January 18, 2009 - 11:48 pm: |
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Kenny,
I appreciate the reply. As of 2 days from original post, The problem has dissappeared. The antenna connections were suffering from green corrosion. I cleaned all connections with a whire wheel grinder, then added some corrosion resistant sealant to the connections and the installation worked as new once again. I assume that the intermittent problem was from the connection being dirty, and when RF was introduced, it somehow caused the connection to bond for a bit. Anyway, as for the antenna, I have no other choice than to install it on the bumper due to height constraints. However, the system has a minimal obstruction by the all fiberglass hood. The VSWR's are good across the 11 meter and 10 meter band (surprisingly). I beleive, though, that this type of install makes me radiate more directionally toward the truck (groundplane) than if I had it completely un-obstructed.
Thanks for the suggestions, and assistance. |
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