To beat a dead horse, cb alt whine

[DEDROBERTS]

I’ve read and read and I still have questions...

Honda Fit, 2015... installed a bearcat 980 CB with a Larsen nmo 27... along with a th-7800. The th-7800 works great, low swr, decent rx through a v and u antenna through a diplexer. The CB has terrible whine that requires the squelch to be closed way too much for my liking.

Have tried tying the 980 direct both leads and with ground to very close ground. Almost zero resistance antenna ground to radio and car ground. Touch the antenna, whine goes away. . Which makes me think a ground issue.

Almost no ripple on the alternator. Voltage regulator seems good.

Hooked 980 to a nmo tri band, whine nearly disappears completely.

Hooked the nmo 27 to a different mount, same whine.

Used a cheap countycomm radio on am and can pick up the whine- closer to the alt the louder.. Used a portable scanner on cb and picked up same whine on a rubber ducky. Hooked scanner on cb to 27 antenna, whine- scanner both on car power and independent on its own battery power.

So- radiated rfi from the alt?

It’s a small engine compartment and the leads run nearer the alternator than not, issue? Re-route as far away as possible? Doesn’t seem like that’s the issue though.

Right now everything is torn down and I hate unfinished projects...

So- any thoughts??

Cheers.

 

[kf4eyr]

no mention of it,,but,,is the anl and nb turned on?

 

[mmckenna]

A properly tuned antenna, like an NMO-27, is going to receive better than the scanner antenna or CountyCom radio will, so not out of the ordinary.
Touching the antenna detunes it, or may be grounding through you, which will thrown things off.

So, I suspect that it's radiated noise from the alternator. It can radiate through the wiring in the vehicle.
Question: Do you only hear the noise when the engine is running? Do you hear it with the engine off and key removed? Do you hear it with the ignition on but the engine not running?

Sounds like you've done some pretty good troubleshooting so far. If I was in your shoes, I'd probably get the alternator checked. Could be the rectification diodes are starting to go, which would result in what you are seeing.

Also…
Make sure you don't have any of the cigarette lighter plug USB adapters plugged in. Some of the cheap ones can be pretty noisy.

 

[prcguy]

Its unusual for an alternator to radiate RFI but it can happen. Are you sure its not spark plug noise? Does the noise make a fast ticking sound at idle then turn into a whine at high speed or is it a whining sound at all speeds including idle?

I agree the Larson antenna is very high Q and touching it will detune anything its receiving. That does not mean the antenna system or its grounding has anything to do with generating the noise.

 

[DEDROBERTS]

Nb anl on- still noisy, no difference.

No noise with engine off. No noise with ignition to accessory-on. No noise with key out. As soon as the engine is on- noise, rate increases with increased gas.

Nothing in any of the cigarette ports.

There doesn’t seem to be a host of examples online (something not on the internet??) of alternator noise vs ignition vs spark plug. So, I’ll do my best to describe it. Anyone remember Atari pole position? It’s a rhythmic knocking sound that increases in frequency with engine revs. It sounds just like the old video games. So, maybe it’s less of a whine? Oh hell, maybe this is a spark plug / ignition deal.

Having the damn fuel injectors and rail replaced Tuesday per Honda recommendation ... never buy first year model revisions. I’ll have them check he alternator while it’s in there.

 

[TenSleep440]

Agree with the rectifiers. Brand new alternator in my Silverado was failing from day one and had a whine. Even with everything properly installed and bonded. New alternator and it’s been quiet ever since.

 

[Chronic]

Try a different CB radio , many have had a golden screwdriver inside them and they are cheap and many lack good filtering .

 

[swen_out_west]

Engine whine can be a bear to fight with sometimes. I had whine on the transmit side of UHF which seemed odd, so I replaced and redid all my connectors and even replaced the alternator.

Was just ready to replace the spark modules and wires when I happened to be doing further testing on the problem and had it sitting in a different location. This is a business radio with a remote face and mounted behind the rear seats of a crew cab. The problem miraculously minimized and when taken further away went away.

Turned out to be the fuel pump. Short of pulling the bed or the gas tank for replacement, I moved the radio, shielded it the best I could and now I am good.

The 980ssb that's in that truck had problems to begin with too, picking it up through the antenna on receive. It was a mag mounted Wilson. I alleviated those problems by rewiring the radio and taking a length of grounding strap from the shielding at the antenna and running it into the cargo lamp so as not to have to grind a spot on the roof.

So having just fought with this problem on a 2007 Dodge 1500 I can sympathize with you, good luck.