I am having an issue with an elevated noise floor on my AM CB radio. I posted this is general because It likely applies to other bands as well.
I get between an S5-S7 noise floor. I have a 102" 1/4 wave whip attached to a metal roof but I get the same noise from a mobile antenna inside the house right by the CB. Both the CB and antenna is at the corner of the house closest to a power transformer on a pole. I get good reception but the noise floor is so high that I have trouble hearing weaker stations. I know this is coming from the antenna as I have run the CB from a battery and the noise is still there. I recently did the ‘breaker’ test to see if there is some interference coming from my house causing it. When I turn off all breakers the noise goes away. When I turn the breakers back on the noise comes back but I could not isolate to any one circuit. The noise returns at different points each time not at any specific breaker. I have also tried connecting the CB in a different location in my house further away from the pole with a mobile antenna and the noise is also reduced. It sounds like I either have to relocate the antenna on the other side of my house further away from the power pole or get some type of filter on my coax. Has anyone had any luck with this? Most of what I see online states that chokes/baluns remove noise caused by ‘common mode’ interference and not ‘differential mode’ but I’m not certain which I have.
Have you tried grounding your antenna and radio (besides the coax ground?)
I have not tried doing an ‘earth ground’ at the antenna but the radio is already grounded by the AC outlet. I can try grounding the antenna and see if that helps.
If you’ve tracked the noise to the house then the antenna is actually doing a fine job. The radio cannot differentiate between wanted and unwanted RF. in simple terms, there is signal on the frequency you are listening, and while impulse noise can be filtered, continuous noise can’t. Your breaker test proves that with house power off, your locality is noise free. If you drive away from the house does it calm down? Curing it is going to be tricky if you’re not an electrician. Often it is superimposed on the line conductors which are switched by the breakers. If it was on the ground, this is independent of the breakers. Finding it and curing it will take lots of testing and enthusiasm.
I grounded the antenna end today and it made no difference whatsoever. Next thing for me to do is get some longer cable so I can connect my antenna on the other side of the house further away from the power pole and see if that helps.
regardless (although sometimes grounding helps) it is still good practice to ground your antenna.
My first thought was that pole mounted transformer was the culprit UNTIL you mentioned doing the circuit breaker test. If you’re able to isolate the noise to just one circuit that would be great! Otherwise, a cheap portable AM radio CAN become a good test tool. De-tune the radio away from any broadcast station. Then the fun begins. Move the portable radio around every part of every room. LED bulb ballasts, fluorescent fixtures, wall warts, light dimmers, actually almost anything that might radiate RF noise. This technique can work, but it will require time and patience.
I would postpone moving your CB radio and buying more coax, until you can isolate the noise source.
Wishing you the best of luck👍