CB interference??

[waverider]

So I finally got tired of sticking my COBRA handheld CB in my tankbag and having the antenna sticking out the corner with cables also going out the bag to a PTT button on my handlebar.... Yesterday I had the BMW radio/CB antenna intalled on the front of the bike (like you would see if you had the radio). I have the cable that came with the CB going from the CB to the antenna and spliced in. The CB is now sitting upright in the empty golve box... a very clean looking install. The CB operates on batteries but I also have it wired into the bike for power. The setup seems to work pretty well and I'm able to talk to and hear people no problem (quite loud actually). So the problem I'm getting is a little feedback (kind of a background noise). It's constant except it goes away while I'm pushing the PTT button. Other symptoms.... It's louder when I have the CB plugged into bike power than just using the battery. Also it's louder when the CB is OFF vs. ON. I'm not sure if there is a grounding issue or not. I was thinking no because I'm still transmitting and receiving OK.... just getting that noise. Any ideas about the cause or solution? Thanks again...

 

Larry

[Scarver]

Are you using the Autocom PTT with your Cobra? If Autocom, what cable part number did you use to connect to Cobra?

 

Just finished install of my Cobra CB to the Autocom. I use a bike mounted antenna, Autocom PTT, and Part 1433 to connect CB to main unit. Was having similar problems but finally managed to remove all feedback and background noise with a custom ground loop isolator. It not only isolates the speaker and microphone circuitry but also the PTT circuit.

 

Share a little more of your setup and we may be able to identify the problem and suggest a solution.

 

P.S. Would also like to see a picture of your glove box set-up - may have to try that myself!

[waverider]

I'm using a Baehr system (Ultima). The CB cable is from them and has a "fork" in it... one goes to the CB (two prong) the other to the PTT button I mounted on my handlebar. How did you configure/make your ground loops isolator? where (in line) did you put it? Thanks, glad I'm not alone

[BerryG]

Did you tune the antenna? You have to make sure your SWR is not too high. 2.0 to 1 is workable with 1.1 being perfect and anything in between is just fine.

 

You can buy a power line filter at most any automotive parts store and that should be in the power line that feeds the radio.

 

If you have the radio connected to an on bike comms system you may have to put ground loop isolation filters on the audio leads (TX and receive..)

 

I would start with the standing wave ratio and work on from there if needed.

[Scarver]

Problem faced by both Baehr and Autocom is that the Cobra CB (mine is the 38WXST) has a common connection between antenna ground, speaker ground, microphone ground and bike ground (when you power unit via PWR connection.) This means that the moment you connect a bike mounted antenna to it, and you are also connected to the Baehr unit, you have a ground loop. Doesn't matter if unit is ON, OFF, battery, or bike powered. So the challenge is to isolate the bike ground from the Baehr or Autocom ground.

 

The Autocom 5-conductor cable handles PTT, GND, MIC, SPKR, and +9 volts. Pressing PTT connects that line to Autocom GND. I used a Radio Shack reed switch with the coil connected between +9 volts and PTT to achieve PTT isolation. Standard 1:1 transformers take care of the MIC and SPR isolation. (Can supply schematic if interested.)

 

Baehr has the PTT switch wired in series with the microphone so my Autocom solution does not apply. But, are you using the PTT switch for any other communication systems? If not, we may be able to try some slight rewiring to see if that solves the problem.

[waverider]

Your explaination sounds about right... The Baehr PTT connection is only going to my CB, nothing else.

[twilmotte]

I have a Baehr comm system and a Midland CB. I grounded the CB antenna to the bike frame in 3 places (in series) along the back of the frame with flat braided cable covered with heat shrink. My comm system and CB radio are grounded directly to the battery. I bought a $10 AM radio noise filter from auto parts store to wire between CB radio and battery positive terminal. And (most importantly) I kept ALL cables and wires as far away from the engine ignition as possible. Also, good idea to tune your antenna as suggested with SWR meter. FWIW. Good luck.