I have a cobra 75, and I'm getting interference with my sub amplifier, when I transmit I hear my voice all over the stock speakers. My amp is only powering my subs nothing else. I disconnected the power to the amp and I don't get no interference at all, everything works fine... A cb shop recommended a "notch filter" but I don't know what the hell that is or where to get one. A Stereo shop recommended installing a switch for the amp, to cut the power, but i dont want to be cutting the power every time i want to talk on the cb, I don't know what to do.. Anyone have any experience in this? Any suggestions?
Thanks in advance!

 

How is your antenna mounted and location?

 

On the tire carrier.. I had a cb shop tune it and everything.. I even grounded my tailgate..

 

Did the CB shop "peak and tune" the Cobra 75, by chance? Often the "peaking" process forces the radio to operate out of its built specifications and can cause increased "spurious emissions" or interference.

There are a couple options to workaround the problem. First, you might be operating with a weak ground. The tailgate can be a challenging mounting location that sometimes has a poor "ground". In this case that means a weak electrical path to the vehicle chassis, which acts as part of the antenna system in mobile installations.

Even if your SWR is "flat" or low, your antenna may have high losses and a poor balance, if poorly grounded. Poor antenna balance contributes to "common mode" interference concerns.

You may be able to get away with using some snap-on ferrites around the wires leading into your amplifier. These ferrites help prevent the "common-mode" interference that is quite likely the culprit. If you get a few "mix 31" Fair-RiteŽ brand ferrites you could potentially eliminate the issue.

 

The cb shop only tuned it.. I will look for those "ferrites" and let you know if it worked, I guess it's similar to the "notch filters" I'm guessing, cause the cb shot said that would block out some mhz..

 

Do you have both the positive and negative wires from the radio running directly to the battery? If you're grounding the radio to a point other than the battery, a ground loop may be contributing to the problem.

The excellent k0bg.com site is dedicated to mobile radio operation and makes for a great read for troubleshooting help. They have a section on ground loops as well as ferrites that can provide additional insight.

 

Cool! Thanks! As soon as I decide to get my butt out of bed, I'm going to ground to my battery, And try that first.. I'll check that site out too.