RFI Chokes..

[DK327]

I have an issue with my mobile cb setup where while I'm driving around in town, I'm getting a lot of interference on intersections where there are traffic lights. Soon as I pass them, the noise goes back down to "normal" level.

I took a couple of long trips recently and all channels were very quiet while I was driving thru the countryside so the RFI is definitely caused by power lines, traffic lights, etc and not the alternator or the electronics in the vehicle.

I read up on how to reduce this type of RFI and found out I might need to get a Mix #31 ferrite (2.4" round) and 7 turns for best reduction...but have a couple of questions:

Where do I place this ferrite on coax? Near the radio or antenna? Do I need more than one? Does it degrade the transmitted signal any? Is it possible that the signal is actually being picked up from power line going to the battery, acting as an antenna, instead of the RF line to the radio? If so, can I use the same ferrite on the power line to the battery? Would a MFJ 915 do the same thing? It's supposed to be 1:1 but I think it would eat up some power?

Any help is much appreciated.

 

[JayMojave]

Hello DK237: This doesn't sound like a RFI issue that can be fixed by installing ferrite cores or bypass capacitors in your vehicle. Due to the RFI having the same frequency as the CB stations.

If the radio and antenna are installed and working properly theres not a lot you can do, you have to take the RFI and the city at the same time. Maybe turn on the NB (Noise Blanker) or turn down the RF Gain, or turn up the Squelch. Or use a DSP Speaker, I run one of these and its a big help:

West Mountain Radio - CLRspkr ClearSpeech® DSP Noise Reduction Speaker

RFI needs a Generator - Path - Receiver if any of these can be eliminated your noise free. However the noise is on the CB Band, and I don't think the local authorities would appreciate you climbing up on the signals posts and installing ferrite cores. (hopefully humor)

As I drive the big city of Los Angles at times I can hear all kinds of noise. Some noises even interfering with the local 2 meter repeaters being received. And that's bad. There is one intersection that has to be a major RFI source / generator as I hear all kinds of noises, beeps, hash, blow torch, and frying bacon all at the same time, on different bands how wonderful. However the DSP speaker does reduce much of it.

The MFJ 915 I believe is for transmitting issues keeping RF off the coax shield. You can try different things such as ferrite cores say at the antenna end, and or the radio end, with the coax wrapped around the ferrite core, but may not make any money doing so. In some cases you just have to live with the noise until we have digital receivers that are programed to eliminate or reduce the noise in receivers. Good luck, let us know what you come up with.

Jay in the Great Mojave Desert... yeah yeah it gets hot here, 103 is predicted that means it will be 110 here today

 

[DK327]

Jay in the Great Mojave Desert... yeah yeah it gets hot here, 103 is predicted that means it will be 110 here today

I bet "patrolling the Mojave almost makes you wish for a nuclear winter" Stay cool and thanks for your response! The product you mentioned sounds good although I'm not too impressed with the price. I think I'll experiment with coax wrapped/clamped around ferrite on both ends and see if it helps any, like you said I just might have to live with it...