That's not really the purpose of the squelch control. The squelch is used to keep the background noise and signals too weak to be useful from making noise in your speaker, which can be annoying in the short term and actually mentally tiring in the long term.

So it's more a hum or whine than crackling/bacon frying, so it's alternator noise. We still need to determine if it's coming in via the power leads or the antenna. With the internal battery nicely charged, unplug the cigarette lighter adapter -- if the noise persists it's coming by way of the antenna, if the noise ceases it's on the power leads. Get that figured and we can go forward from there.

While throwing a reactive filter on the power lead can often work, it's not at all uncommon for alternator noise to be due to one or more failed diodes in the alternator's rectifier. Should that be the case, the best fix is to address the failed rectifier before the failure cascades and potentially gets more expensive. Should you end up needing a noise filter, though, you can pick one up for five or ten bucks that'll be good for ten amps or better and just wire it in. Most of 'em come with instructions that would have you wire the filter in somewhere near the battery, but I recommend getting it as close as is practical to the powered device -- or in this case, the power outlet. Another option would be a filtered cigarette lighter adapter, though you might have to fabricate a bit to get the right plug on the radio end of it. If you want to go that route (and make it so that the filter goes with the radio rather than the truck) and have trouble finding such a critter, check out some ham radio shops.

But my advice is to figure out whether or not you've got a failed rectifier first, and then to determine how the noise is being coupled. Just throwing parts at the problem is the least efficient way to go about it, and if you don't actually need the power filter then you're better off not adding additional points of failure to the system.

 

Ok, don't laugh. No really.

1. Connected to whip and used aux power source. Hum was there that matched engine rpm.

2. Same as #1 but cig lighter power source. Same result.

3. Disconnected whip and power source. Put on battery pack and bnc connecting antennae. Hum still there. LOL

In all of the above, squelch does cut the hum out with the other background noise. No crackling/bacon type sound.

The test isn't exactly what you wanted as I couldn't get the whip connected and to use the battery pack.

*throws hands up*

 

Sometimes a bad design or failing unit will have antennas in unintended parts of the circuit and will behave like you describe. Next test, swap radios.

Re the antenna pics. As was said, ideal is actually a bit more than the 102" whip. I'f recomend one of thse 6 inch springs in that stackup you've got there as both added electrical length to get you slightly better impedance matching to the air but also to help relieve strss on the antenna when you decide to bend it over and tuck it in.

 

So there ya have it: It's being coupled by the antenna (or at least through the air) rather than the power leads.

I'd start out by walking up on other running vehicles with the rubber ducky antenna and internal battery pack to see if the thing hums along with many or most. If it does, then I'd wonder about getting warranty service on the radio, or if Midland's quality has gone to crap and you're the unlucky winner of a bad purchase decision. (Midland is the CB radio manufacturer to whom my father awarded his loyalty -- the old man was big on brand loyalty for everything. But then he's dumber than broiled dirt...) Maybe you can find another of the same model and walk it up to your truck? If I wanted to try that I'd hope to find a CB radio shop in the area that's a Midland warranty station and also sells that model -- most radio shop guys are pretty reasonable and happy to help.

If that narrows it down to not the radio and just your truck, or just one or two vehicles of ten or 15, then I'd proceed by first checking out the rectifier in the alternator just to rule it out. Then if that's ruled out, I'd be looking at grounds, all of the grounds under the hood tying the block and the battery together and to the frame and chassis. There are a group of them to look at in these trucks. You want to ensure that they're all there, the conductors are intact, and the connections are free of corrosion and solid.

About, oh, eighty or ninety percent of the time when I fixed an engine noise problem in a radio it was by getting the grounding right. I kept braided stainless steel ground straps in various lengths in stock because I used them so often.

As you've probably surmised by now, hunting down electrical noise can be a real PITA. I've got war stories galore about electrical noise. I'll spare ya.

 

In the old days generators caused a lot of noise in car radios. The first ones actually had permanent magnets in them. Later they converted them so they had electromagnetic field coils in them to hold down costs over permanent magnets, and a mechanical voltage regulator to make the 6 and later 12 volts needed to maintain the battery. It didn't take designers long to figure out how to put a capacitor on the generator to bleed off the alternating current byproduct being produced by the direct current device.


Then one day a bright young fellow developed the Alternator. It produced AC {Alternating Current} voltage that had to be converted to DC {Direct Current} using the new, at the time, semiconductor diodes. Filter capacitors were used to remove the AC ripple in the current.


That is the whine you are hearing,... probably.


In these new vehicles there are a whole bunch of things that produce all manner of electromagnetic noise. In my HHR there are no less that 4 onboard computers if you don't count the processor in the stereo.


Any of those can cause undesired noise in radio.


Do a search for ham radio sites then search those sites for mobile radio operation and mobile radio noise in particular. Not so long ago on my favorite ham radio site, QRZ.COM, there was a fellow fighting errant noises in his mobile setup. He had a Ford Excursion for vehicle.


He did all manner of things trying to get rid of the noise in his radio. Finally he started grounding things with braided copper he stripped from RG-8U coax. He put grounds on all the frame components to the body tub, the doors, the rear hatch, the fenders and bumpers, even though conventional wisdom would say those should be grounded already, also the hood over the engine, the shocks and struts, all the axles, and finally the exhaust pipe at several spots along its length.


When he finally put a strap on the last section of the stainless steel exhaust pipe the noise went away.


The pipe was welded to the rest of the exhaust so it should have been grounded by the braid further up its length, you would think, but it needed its own ground strap at the end to be quiet.


I remember my dad making a manifold sort of thing out of copper tubing to run the ignition wires though on the Pontiac Chieftain he had trying to kill the spark noise he was getting in the radio.


Finally they started making resistor plugs and wires that fit his straight 8 and the noise magically, mostly, went away.

 

One other idea popped into mind. If this coax, between radio and antenna, has followed the problem then well...

Leaky coax is definitely a place for differential problems to creep in. Walked on, kinked, or just generally abused cable should be tossed.

That brings up an old radio guy trick I once heard. Since coax is never perfect, some guys like to cut it in wavelengths or fractions of to ensure the leakiness results in positive gain not negative. It turns out to not be a such huge thing when cable quality is excellent though but some of these guys are all about every advantage they can get out with.

 

I have no idea what that means.

We cut coaxial cable at odd half-wavelengths for impedance matching -- that is, keeping everything in the transmission line as close to 50 ohms as possible. Where there are impedance mismatches in a transmission line, some fraction of the power is reflected back toward the transmitter, which is bad because (a) it's not radiated into space where you want it to go, and (b) the final amplifier stage is forced to dissipate that energy as heat which ain't good for it.

 

There is a whole lot of bunk involved with radios in general and CB's in particular. Cutting length of coax to a specific wavelength or portion of a wavelength is one of them.


There are special circumstances where tuned stubs are used but in such a short run as in a vehicle there is no advantage to having a particular length of coax. All you need is enough to reach between the radio and the antenna.


Generally the shorter that length is, the better.

 

I read/hear your claim loud and clear but completely missed any technical supporting argument.

My understanding is this is a fairly well documented and repeatable effect though I make no claims of having any supporting evidence one way or the other myself. I've talked myself into believing the theory which seems to stand up to my technical scrutiny. Since I'm a bit of a geek for the stuff I'd be interested to hear the technical reasons why you are saying ths isn't a real effect. I think I clearly described my position but can elaborate if not clear enough.

EDIT: a quick google search reveals this controversy. I see some pretty good technical explanations claiming this is just a method of fooling swr meters. Still wondering about the truth as should be measurable with sme more expensive rf metering equipment.

 

its pretty funny. all this talk of cb's and now i think i found a cb that i want to try finding for my truck.