RF Gain and Squelch

All CB Radios are going to have "rain-static" or "White noise"...The more you turn up the RF Gain, the louder it's going to get...That's just part of it...And if your around certain types of street lights, or electrical lines, the more static your going to hear...

The RF Gain is to pull in weaker stations, but it will also make the static louder, just no way around it...

Another problem can be with your antenna, like stated earlier, some antenna's are worse than others when it comes to the static, but that could be because they actually are working better at pulling in signal. Your radio can't really distinguish what is signal and what is just noise...

Also as stated earlier, Solar Flare's has allot to do with the noise level too...If you notice, after the Sun go's down, usually you will have allot less static in your receive...

Another problem is not all radios are created equal when it comes to filtering noise...Some radios have better filtering, but even with those, the static will still be there.

 

I agree, that is what my experience shows as well!

 

Some radios have the squelch partly determined by the RF gain. Others have it less determined by the RF gain. It's never described in the owners documents. Only by looking at the schematic could one tell what is really being done.

Most radios have ANL automatic nose limiter and some also have a NB noise blanker. The ANL is a cheaper circuit and simple. The NB is more complex. Either can be adjustable, but on CBs they usually are not and the factory has selected a good compromise.

The ANL reduces loud repetitive buzzing and the like, by clipping or limiting the size of the received signal, the goal is to reduce the noise signal's peaks and pulsations to just the amplitude of the desired average audio signals, making the noise seem quieter and letting more of the voice through. You may notice the speech is slightly less 'fidelity' when this is used, but still very good.

The NB is more complex and it detects the high audio frequencies and fast-rising waveforms that exist in pulse-type noises like ignition noise and arcing, and, triggered by these pulses, mutes the signal for a very short time, perhaps 0.001-.005 second, until the individual pulse is done with. The effect on the desired voice reception's fidelity is not too bad.

There are many kinds of noise blankers. An advanced one is called a noise coring amplifier. This circuit detects the fast-rise waveform of a noise pulse and follows the noise pulse over its entire cycle. When the noise pulse reaches up to a certain level, the output is muted, and when it drops back below a certain level, the output is un-muted. Unlike a simple noise blanker, it is not done by triggering a time-defined mute function, but acts upon the pulse for its actual duration. This allows it to respond to noise pulses of varying lengths. The advantage is clearer when one considers that noise pulses have widely variable lengths and amplitudes. These are seldom found in CBs.

Other noise reduction:

DSP - There exist some external/remote speakers for all kinds of radios, that use DSP digital signal processing. This will have inside it a board with an IC (or a few) and an audio amp. The signal from the radio, with all of its noises included with the audio signal, is fed into the IC chip, which is a sort of computer that 'knows' what a voice or audio signal looks like, and what various kinds of noise look like, and it memorizes the signals coming in, into little digital samples. It does this tens of thousands of times each second. Then it decided what parts of the samples are voice and what parts are noises, and plays just the desired voice signal out through the external speaker and throws the noise into the bit bucket where you don't hear it. These used to be very expensive but are now only expensive, maybe $150-250. I would recommend it to those who suffer with mobile noise but want to leave the radio on all the time anyway. Ham operators sometimes use them in their mobiles, despite having more high-tech radios plenty of noise can still come through. I do not own one but played around with them and they do work. One person complained that the voice did not sound completely natural, but that's not the point. The point is to be rid of noise. Before buying one, listen to one and see if you like it.

 

Again, M818 pretty much got it dead-on.
Any noise that gets reduced (in your receiver) if you uncouple the antenna lead from the radio means that it's RF noise, same as the stuff you *want* to hear. ANL & NB can have some benefit, but not without also compromising your receiver's ability to hear what you want to some extent. ANL clips off the loudest peaks of impulse-type noise, but if you think about it, a voice signal seen on an oscilloscope also has peaks. As long as the signal you want to hear is louder/stronger *on average* than the interfering noise from fluorescent lamps, digital display drivers on fuel pumps, electric fence power supplies, Part 15 devices (home entertainment gear, home remote control systems, dog training collars, wireless doorbells, PS3 gaming consoles -- basically *anything* with either a radio/TV transmitter or receiver meant for very short range use) -- you'll hear "the other guy". But add all those other RF generators, and at some point as you drive past some huge "lump" of them, that's what you'll hear instead of the Good Buddy two miles ahead.

Some sorts of RF interference are incumbent upon the transmitting agency to reduce to lawful levels -- so-called "unintentional transmitters". Power grid systems, with dried-out transformers, cracked or arced-over insulators, bad grounds, corroded galvanized guy wires, etc., are among some of the fairly common sources of RF noise that's heard in "our" spectrum, whether it's CB from 26.965 to 27.405, or hams from 500 Khz, and big chunks from 3.5 to above 24 GHz. Most of the interference we get is between 3-30 MHz, and a lot of that can be located pretty easily with a simple AM broadcast receiver.

But as for the kinds of noise you're hearing, the best news is that, in most cases, you'll drive through its area of effect soon. If you have to set up a base station near one of those sources, the best way to approach a solution may be a visit to the folks who run the offending device and have a friendly chat about alternatives.

Just a thought. They occur so seldomly to me that I usually try to write them down before they pass through my head unimpeded by the memory process and just disappear into the ether....

73

 

Funny you mention this....I installed a very cheap Maxon MCB-30 in my winter beater truck....you can open the squelch and barely hear anyone.....it's as if the coax is unplugged....but when a semi decent strong signal comes in, they sound clear as a bell....no one seems to know if this is just how this radio is or if it just has a receive problem