Engine Noise During CB Use

[twilmotte]

Just wondering if anyone has any advice on what type of noise filter might work to eliminate (or reduce) engine noise creating high pitch whirring and crackling when I use my CB radio on my 1150RT. The comm system is a Baehr UltimaXL. I have no problem with the noise while listening to music or while using my GMRS radio. I think it's playing havoc with the AM radio (CB) waveband. The CB radio is a Midland 75-822. The antenna is a Firestik Firefly mounted behind top case and grounded well to the frame under the pax seat.

[Tool Man]

Hi Tom and check your e-mail.

 

First off...AM sucks as far as trying to eliminate noise. Have you powered the CB directly to the battery? The battery is your best filter. Your four grounding wires..how long are they? if they're too long and multiples of four you could be picking up a third harmonic of 27mghz. The best ground for your application would be a 3/4" or 1" wide ground strap material. It's less prone to pick up a harmonic and you may even notice some vehicles have been using this under the hood....that's the reason. Round wires for ground in a transceiver application is no good for low frequency use. My entire Ham station is grounded using 1" wide ground strap material to a large aluminum plate and from the plate there is a 2" wide piece of copper ground strap running from the plate to a 1" diameter copper stake in the ground. The reason for this is that I operate on low frequencies down to 3.8 mghz. The lower you go in frequency a higher quality of ground needs to be used.

 

Additionally you mention running the coax to the front of the bike into the tank bag powered by a cig adapter. I suspect this could be the problem especially if the cig adapter is not run directly to the battery.

 

Here's what I would try:

1) ditch the cig adaptor and use a Motorola (available at any Radio Shack or equal) connector for your disconnect. RF can enter cig adaptors very easily. Run that directly to the battery and do NOT run the power lead anywhere near a motor electrical source. Such as spark plug wires, alternator wires, fuel injection wires etc. Even stay away from the wires coming from the tank for the fuel indicator.

 

2) ditch the four ground wires and run a single 3/4" wide ground strap from the antenna mount to the battery or frame.

I doubt your SWR will change and the frame should give you sufficient ground plane.

 

3) If these attempts don't fix your interference This Will use model PC-10

 

Let me know how it works out...

[twilmotte]

Thanks, Mike. I'll try your suggestions and let you know how I fare. I really appreciate your rapid reply since I'm eager to attack the problem (after I get back from riding the Ozarks this week end).

[Tool Man]

Tom....I forgot to mention one more thing.

 

Keep your coax seperate from the power/ground wires and also away from the already mentioned inteference generators. Run the power leads on one side of the bike and your coax aong the opposite side, preferably along the frame and not zip tied to any bike related electrics.

[twilmotte]

Thanks again, Mike. I'll follow your suggestions and let you know how it turns out.

[twilmotte]

I'm making progress ... I rewired the braided ground strap from the antenna mount across the back underside of the luggage rack along the left side of the bike under the pax seat (away from the coax antenna cable, which runs along the right side of the bike) and grounded the antenna mount in four places, wired in series. I also re-routed both the PTT cable and radio/cassette player output cable further away from the engine cylinder heads (up along the gas tank under the t-ware). Then I tried using the CB radio with both the engine off and engine running -- tremendous improvement!! No discernable engine noise. One or both of these actions really cleaned out the noise I was getting while transmitting with the PTT. I have a test ride set up with my neighbor on Friday morning to ops check the CB out on the road. I am still prepared to hard wire the CB radio to the battery and install a CB/AM noise filter in line, but I may not have to do that now if the CB works well using the accessory plug power on the Friday test ride.

Also, I took your suggestion and ordered a Newmar PC-10 noise filter from Marine.Com and will install that between the battery leads and the Baehr comm system to clean up the small amount of noise I get when riding and listening to music. Things are looking (sounding) better -- thanks again for your advice, Mike.