I just installed a CB radio in my truck, im goin full on redneck :lol:

Anyway, im getting all this interference from my truck, from whenever my spark plugs fire. Ill admit it sounds kind of cool when im accelerating and i hear the engine going and the rip-roaring noise that my CB radio makes, but i cant hear anyone else on it :lol:

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I'm no electronics god, i just talk too much.

 

Zach, you have a good demo here how the early spark gap transmitters worked :wink:
Has your car suppressed spark leads (or plugs)? If not you may have to fit some.
It is also a good idea to fit inline suppressors to the 12v leads, as close as you can to your 27meg set. These are usually just a toroid core with both leads wound around as often as is possible to fit the wires through the hole.

I have no engine interferance at all in my 27 Meg set but then my truck has a diesel engine :lol:.

good luck

Klaus

 

I also have this problem, Do you mean the 12V leads the CB is connected to?

and what are "27 meg sets" - ah is it the freq for the toroid core :P

BTW - my real name is also "zack"

 

Thats what I was thinking :wink:

Suppressors on BOTH negative and positive? I hope that'll solve the problem. Shouldn't the CB set already have some sort of suppression like that, seeing as its main use is in a vehicle and the engineers should have foreseen that. Maybe ill just make my own, i have some toroid cores laying around. On the other hand CB sets are usually used in diesel trucks, and they don't have spark plugs.

I'm pretty sure I have suppressed spark plugs because this interference doesn't come over the AM radio.


I think 27 meg sets are just CB radios. I believe thats the frequency thhhey run at.
My name is spelled with an H at the then: zach, so at least i still have some individuality :lol: [/quote]

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I'm no electronics god, i just talk too much.

 

27 MHz is the nominal transmission frequency of the CB radio. Also referred to as "AM" CB. This is in contrast to UHF CB, which operates at 477 MHz (at least, in Australia. Other countries may use different frequencies).

 

There 'may' be suppressors inside your 27Mhz transceiver (='set' :wink but there were none in mine (el cheapo).
You can easily test if the interference comes via the power leads by powering the 27Mhz transceiver temporarily from a separate 12V battery.

AM radio frequency is 0.5 to ~1.5Mhz and 27Mhz is, well, 27Mhz - big difference - and your AM radio may have better suppressors built in as well.

Do check your trucks ignition system, if it still uses points check if the capacitor (condensor) there is in good condition. Check the spark leads & plug caps for poor connections.

Do you get alternator whine interference as well?

Klaus

 

On accessory setting on the ignition (engine not running) My CB works PERFECT. As soon as I start my truck up you can hear a high Frequency hum . My truck is an 1991 Ford Ranger XLT 4x4, 4.0 EFI V6 - Solid State ignition :shock: I dunno why I'm having this problem.

 

yup, i hear the alternator as well. When I turn off the truck the interference dissapears. Ill let you know how it goes when i get those supressors.

Oh yeah, and do I put suppressors on BOTH negative and positive?

__________________
I'm no electronics god, i just talk too much.

 

Two different problems. Same solution:
fix it at the source.
The RF interference is originating in the
ignition system - possibly a bad spark plug wire
or distributor cap. This is generally a "ticking"
sound. If you can hear the separate ticks at
an idle, it is probably a wire or plug, otherwise
it is in the coil, coil wire, or cap. RF noise is
radiated to the antenna. B+ suppression will
not help much here.
The alternator noise should only be obvious if
one (or more) of the diodes in the alternator
is bad. This is more of a "whine" in the audio.
Suppression devices in the B+ (+12v) lead
to the radio may eliminate or reduce the noise,
but the problem remains. Do NOT add anything
in the GND lead. You MAY run it through a
ferrite core for EMI suppression.
<als>

 

I'd bet that most of your noise is getting in through the power wiring. You can get a filter for the 12V line from Radio Shack and it should take care if it. It'll consist of a torroid inductor and one or two capacitors that act as a low-pass filter to let the 12V in and keep the alternator whine and ignition noise out.

The older Radio Amateur Handbooks from the 1960s and 1970s used to have sections devoted to curing that stuff in mobile rigs. For taking care of the really sensitive receiver problems, they would actually build shields for the distributor and coil and run the spark plug wire in braided shielding. You also used to be able to pick up static discharge interference from the tires.

U.S. CB on the 11M band ( around 27MHz) is mostly AM but they also have SSB transceivers that are legal. You're limited to 5 watts but because of lax regulation and monitoring, there's plenty of illegal linear amplifiers in operation. Never did understand why those jokers didn't take the initiative to get their ham license.

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

Dean's idea is probably what will cure the noise from the alternator, I have used those before.

One idea that I have had some success with also may be free if you have some computer junk about. Many keyboards, power supplies, and other peripherials have a ferrite bead molded onto their cord. It's a tubular section about 1 1/2" long and 3/4" or so in diameter, usually right near the plug, or internal on many keyboards. Remove it from the cable, and pass the positive power lead through it, relooping if possible, as many turns as you can squeeze through.

It may not be as effective as a proper choke and cap filter, since it is designed more for higher frequencies, but if you have one laying around, it's worth a try and it is free.

 

Zach.. One more thing, did you take your positive CB lead all the way to the battery? Most manufacturers reccomend getting the power directly from the battery instead of tapping off of the fuse panel, cuts down on interference and voltage drop especially on transmit. Route the wiring away from the engine and be sure to fuse it on the battery end..And like the above posts you may have an ignition problem that may need attention. But you should have good wires/cap/plugs for better gas milage if nothing else

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gerty

 

First be sure, which way coming the trouble: via aerial and/or via supply cable. Use independent battery for testing, start the engine. If You also hear the noise, this coming via aerial, and need trouleshooting in the ignition system.

 

does anybody have a wiring diagram for speaker/mic units for handheld cb radios.

ta

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Every little bit counts! It works with money, and it works with electronics!

 

i have had this problem in the past several times. its probably a bad diode in the alternator as already said. there are six of them in the altenator so it still puts out without a problem but with electrical noise.i was never able to filter the noise out i just had to replace the alternator ( or the diodes if you feel like it ).