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Static / buzzing over car speakers when keying mic


s7427p

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Hello everyone,

 

First let me apologize I swear I used the search forum tool to try and find this answer and either it hasn't been asked or I'm not searching with the right words in the search bar.

 

On to my problem. I have an midland MTX400 installed in my Jeep running a CMET CA-2X4SR 146/466 MHz dual band antenna. The cable I'm using is a 3.5D-QEFV FUJIKURA-DIA. The radio power is coming from the battery and the ground wire is going to the frame. 

The antenna NMO mount is mounted on the tail gate via a steel mounting bracket the paint has been removed to insure a good ground along with the bolt holes being tapped to remove any paint. Just to be safe I ran another grounding wire/strap from the tail gate to the body. The cable is routed along the roll bar to keep it away from any speaker wire or speakers. The radio itself is mounted above the rear view mirror.

 

It should be noted that I do have an amp running the car stereo speakers. Its grounded to the frame and is getting power from the battery.....not sure if that info was needed or not. 

 

When I key the mic I get what sounds like static or buzzing coming from all car speakers. I'm pretty much at a loss as to what and try to chase down next. I'm told that when I transmit I'm crystal clear and same when I'm receiving transmissions...everyone sounds fine. No one says that they can hear this static / buzzing that I hear when I transmit.  

 

Any help would greatly be appreciated.

 

Thanks in advance!!

 

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The ground for the radio should be going back to the battery. Well at least what I do for my installs.

 

It sounds like a ground loop was created. Check the resistance on the grounds of the amp and the ground location.. The power leads, signal leads and speaker wire can act like antennas. Is this only occurring when the amp is on?

 

The antenna, grounding wire from the mount to gate to the frame. Aren't for electrical grounding.

 

Essentially, you created continuity between those components to create a larger ground plane. Think in the terms of a reflective surface for the radio waves. In actuality you are basically creating the other half of the antenna.

 

 

Sent from my SM-G975U using Tapatalk

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update:

 

I did some more digging around, sound is only coming out of the left rear speaker.... I switched the rear speaker wires at the amp and keyed the mic the sound then came from the right rear. switched the wires back and unplugged the RCA plugs 3 and 4 going into the amp coming from the car stereo.....keyed mic and sound buzz is coming from left rear. So if im not mistaken it sounds like the amp is at fault picking up on the frequency and broadcasting it to the left rear speaker.

 

Also the buzz / static is pretty quite on channels 1-7 jump up to the repeater channels and its really loud.

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Do not run the ground the battery. Make sure its on a chassis ground. The antenna you list is a amateur radio antenna. You are getting RF in your amp most likely from the cables. Have you test VSWR on the antenna. You could try some ferrite beads on the AMP input cables.

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