I have a Cobra 75WXST CB radio and I am trying to find a way to reduce the noise level coming from the unit. The SWR is 1.2-1.5 through out the 40 channels, I am using a Tri Band power antenna-adjustable plus trimmer, the remote unit is grounded with a ground wire, the Coax cable is not located near any power wiring and the car stereo system has no noise problems. Any ideas?

 

where is the antenna mounted? The closer to the cab it gets, the higher the swr's can get. Also on the bumper isn't the best place for it either. 1.2-1.5 isn't all that bad really though. Not familiar with that style of antenna, what brand and such is it? Also the coax isn't wrapped in a coil somewhere where it's tucked away is it?

 

The antenna is mounted on the front passenger fender in the stock position. The Coax is not coiled and is isolated from any power wiring. The antenna is a Harada MT-2 tri-band unit with top adjustment and a trimmer is mounted inline-antenna lead plugs into trimmer and the trimmer has adjustmen pots for CB and Radio. The antenna is grounded to the body via mounting and a cable to insure a good ground and the base unit is grounded via cable to the body.

 

I have the same radio (now) and it is dead quiet:
- http://www.4crawler.com/4x4/CheapTri...na.shtml#Power

 

It's the antenna/splitter, I understand what he has now. AM/SSB/FM antenna. I don't trust those things.

http://www.firestik.com/Tech_Docs/am-fm-cb.htm

On a side note, is this the "splitter" your using? If not, it's supposed to be the "best" one out there, but your never gonna get the squelch and/or SWR down as if running just a standard CB antenna.

Firestik AR-1A Matchmaker http://www.wearecb.com/store/firesti...ter-p-220.html
This allows you to use a regular CB antenna with your radio. No need for one of those 3-ways.

 

If youre still having problems i'd suggest twisting your power wires and running them directly to the battery. Electronic noise can be introduced by anything connected and the power wires can act as an antenna. The CB can interpret low freq power signals as a voice signal.

Dont use common ground bolts or wire your power to the fuse box. Thats not to say you CANT use those spots, but if you're having problems with noise it can help to run them straight to the battery. Thats how mine are run.

 

run some better ground wheres from your battery ?

 

Wait, what type of "noise" are we talking about you having? White/squelch or EMI interference as there is a big difference on how to combat it.

 

My SWR readings are 1.2-1.5 going 1 to channel 40. The SWR at channel 19 is 1.1. The CB power + & - is direct to the battery. I ran a separate ground wire from the base module to ground even though the base is mounted on body steel. The antenna has an adjustment on top that (adjustment is in / out or shorter / longer antenna) is adjusted almost all of the way in (short antenna) which resulted in 1.3 SWR at channel 19. I then adjusted the trimmer to achieve 1.1 at channel 19 and produce the SWR readings of 1.2-1.5 1 through channel 40. I adjusted the radio portion of the trimmer and have no noise. I will try twisting the power supply wires from the battery connection. I do not pickup noise from my radio when my stereo radio is tuned to AM stations. The coax cable is not coiled and is not located near any power wires except for under the dash which the closest 12V+ is wire is the radio power wires that are about 3"-4" away. Noise is static noise. I do not have ignition, alternator or engine whine noise.

 

I stand by my previous statement. It's the type of Antenna/Splitter your using. As if this was a noise coming through the power source it would not go away by simply switching to AM on your stereo.

 

I guess I should run a regular CB antenna direct. I do not want to drill any holes in the body so I could mount an attenna on my rear tube bumper. What antenna system do you recommend?

 

no need to drill holes with this: http://www.wearecb.com/store/firesti...unt-p-310.html Should fit right into the stake pocket in the bed. I like my Wilson 4ft Flex antenna.

 

I do not have any stake pockets in my bed. Thanks for the suggestion though.

 

you can always make or buy one to go onto the fender bolts under the hood. Look around for some ideas of no hole mounts. They might even make a clamp on one for the bed similar to how a bed cap works. This is for your show truck the one in your avatar right? I never did like the ides of putting one on a bumper as the bumpers usually don't provide a very good ground plane for the antenna.

 

Yes, the CB is mounted in my show truck. I chose the Cobra CB radio because it does not require much space and I could mount it on the center hump with a custom bracket. The power unit is mounted under the passenger seat and I could run a new coax cable through an outlet behind my center console where my wideband oxygen sensor wiring comes in; no high voltage wires there.