CB Radio Interference

[Storm Chaser]

I was wondering if anyone has encountered this slight problem with a CB. Every time I apply the brakes, a second later there is a few seconds of static that comes through the radio after I disengage. It happens on all channels. I ran the coax and power cord under the front of the dash and is rather close to the dianostic port. I have no symptoms when I transmit. This seems to be the only thing affected. Any ideas?

[GPan099]

It's possible that it is coming from the 12v power lead.

The "cleanest" power is a direct line (fused) from the battery or fuse panel.

Where did you tap into for power?

Also maybe a bad ground.

[Storm Chaser]

I ran a pos and neg lead directly to the battery because it is a high power 10/11 meter radio. Ran the leads through a hole in the firewall that I created and underneath the I/P directly behind the diagnostic port. The radio receives and transmits flawlessly. It is a strange type of interference immediately after I disengage the brake. I may try to reroute the wires tomorrow but it sounds like the radio is picking up some type of internal communication from within the vehicle. Thanks. Any more ideas?

[f5fstop]

Could be interferrence with the brake booster motor (H3 does not use vacuum for boost, it uses a motor). It is located right near that big grommet in the dash panel. Can you re-route the wire away from the brake system?

This may not be the problem, but it is the only thing I can immediately think of with only three cups of coffee in my system.

[Storm Chaser]

Now that sounds like the likely culprit. The interference does have the characteristics of a motor and the coax/power crosses that area. It may be hard to relocate but I will take a look. Have some more coffee and thanks.

[Big Z]

Might try installing a Filter.

[Hunner]

Radio Shack used to sell an inline filter transformer. You ground it and hot wire runs thru it to filter spark and ignition noise and might help this also. I used to hava Land Cruiser 1970-1980 and before I got one of these you could hear the plugs firing and speed up with acceleration. See if that is still available.
While your at it you should check the SWR of the antennae. I ferite coil in a couple of loops of the coax can help eliminate strange interference also.
Or it could be aliens!

[Storm Chaser]

I think the first thing I will do is disconnect the antenna to see if the noise originates from the power leads. That should tell me where to start. A filter would be an easy fix. I believe Radio Shack still sells them but sure they are available on the net. Re-routing the wiring is not an easy fix in this installation. Thanks.

[Storm Chaser]

I disconnected the antenna at the radio as well as unscrewed the antenna from the mount. On both occasions, the noise disappeared. I also temporarily rerouted the wires away from the brake mechanism and the noise remained. I am convinced it is coming from the brake booster at this point. But, it seems to be originating from the antenna rather than the power. Maybe I can find an RFI filter for the antenna somewhere or try another antenna.

I did find a ferrite snap on choke for the coax at Radio Shack http://www.radioshack.com/product/in...032058.2032230 and thought that would be an inexpensive attempt to solve the problem.

[KB7TCV]

Depending on where the antenna is mounted and the length of your coax you can run the coax up through the bottom of the frame. If you pull up the plastic trim piece where the door meets the truck there are a couple of spare holes that a big enough that you can run your coax through. If that doesn't work and you have some slack in your coax try coiling it up about 5 - 6 times so you have about a 3-4 inch coil and tape should help eliminate some of the interference

Reed
KB7TCV
Northeastern Utah

[Storm Chaser]

Glad to meet another amateur and thanks for your help. The noise is definately coming from the brake booster. The choke seemed to help some but did not eliminate it completely. It is tolerable at this point and will not happen during open driving when I am likely to use the radio. I am wondering if a top loaded antenna would eliminate it completely. Right now I have a side mount firestik mounted to the front ds just above the GM emblem and have to remaining coax coiled into a balum inside the fender well. I also wired a redundant ground from the mount to the chassis and have a good solid electrical ground. In the near term I will be installing a dual band 2m/70cm radio and gps navigation and wondering if the interference will affect those units as well.

[KB7TCV]

Do a search for cb or ham radio on this message bord for more help. If you will run the coax through the frame rail and up under the plastic trim it should eliminate the interference. For a dual band setup i would suggest the ft-8800 remote mounted with the contol head up front and the radio in the back. I you need additional help look up my call on qrz.com and email me direct off the board.

73's

Reed
KB7TCV
Northeastern Utah

[Storm Chaser]

I have included a few pics of the installation. I used a lowboy mount on the dash so this is a temp/perm installation. That should leave room for the other units under or beside the dashboard. I also included the installation of the PA under the hood. I think I will wait to relocate the coax when the other radio arrives. I will be seriously looking at your suggestion for the dual bander. I will keep in touch for sure.