Posted: 7/18/2006 5:24:30 PM EDT
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Never really messed with these things, but I need one to keep in touch with the shop. So I stuck an old Cobra unit into my wrecker truck today. Only problem is there seems to be some feedback that becomes higher-pitched the higher my truck revs, and it gets different/worse once the electric fan kicks on. Yes, it is wired straight to the battery. CBs/stereo stuff is not my strong point, so I'm kind of fucked...and my brother, who does know these kind of things is in Japan until October.  Help? |
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Are BOTH wires running straight to the battery? If so, you're probably just running the wires too close to a noisy part of the ignition system. Try running the wire a few different ways, and see how that goes. I've actually used coax to provide power, where noise was really bad. It works.  Sometimes the whine is a blessing in disguise. Once I used it to correctly determine that my alternator was about to fail.  I don't know which model Cobra you have, but make sure the ANL and NB circuits (if equipped) are switched on. |
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It's ignition noise (varies with engine speed) and good old electric motor noise. It is most likely coming in from the battery connection. Google "CB noise filters" and you'll find a lot of listings for power line filters. There is also a slight chance it's coming in through the antenna. You can check that by disconnecting the antenna (DON'T TRANSMIT!) and see if the noise is still there. If it is, it's coming in the battery connection. Dave |
We got us a beachball buggy funny bunny taking pictures on the other side of the mixmaster. I need a 20 on a double L and some motion lotion. I just got a pumpkin in the middle of a window washer, and I'm late for my date at the outdoor tv, come on? (It's like white guy jive, or something...a lost art) |
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Okay, I grounded the unit's chassis, checked the body ground, and took the ground off the neg battery terminal and attached it with a ring terminal to one of the seat rail bolts. No change in the noise. Looks like I need a filter. On a related subject, I found an old PA bullhorn that I am considering stuffing under the hood. Only problem with that being that it has a pair of stripped wires and on the back of the CB unit, there is a headphone type jack. Do I just rob one off a pair of headphones or what? |
You can buy a package of 1/8" mono plugs at Radio shack for like $1.27, or some such thing. Or ya - rob it off a set of old crap headphones. That works, too. 
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If your CB has an ANL or NB switch, make sure they are turned on. The ANL is an automatic noise limiter and the NB is a noise blanker. The higher end CB's will have these switches on the front panel of the radio. Turning them on will greatly reduce the received noise. I know from personal experience that Ford trucks have a very noisy electric fuel pump. It all but kills the receive on most CB's. To see if you have this the problem, unhook your antenna and see if the noise goes away. If it does, you need to filter the noise at its source. Ford has a kit that you can install on the pump to cure it. |
The 428 in my wrecker pumps it's fuel mechanically. This must be an el cheapo Cobra, since it only has 2 switches and 3 knobs.
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