Re: CB Radio

richard wrote:
I have been involved with CB radio ever since I was 12 or so. I never had the equipment to get inside and work on them though. While I have had a couple of linear amps in my time, neither were more than 50 watts or so. If you're pushing more than the 4 watts allowed out of the box straight, you're violating the law so you may as well have a linear.

I once designed an amplifier, using tubes, 3 of them, that would have a total of 900 watts output. I took that design to a tech and asked him if it would work or not. He said it would. The problem was, finding the right transformer to do the job. Oh and the drive power required was a mere 4 watts. It took better than a year of searching before I found that transformer. The other problem I soon found out was getting the tubes. They were hard to come by and expensive so I dropped the idea. I also designed the amp so the tubes were put in parallel so I could add more later if I wanted.

As you know sir, linears are illegal now below 50mhz. So if you have one, you could not only lose the amp, but the radio as well and pay a hefty fine for your troubles.

Yessir, Mr CB Cop, that's important information. Thank you for providing that.
FYI, linear amplifiers have ALWAYS been illegal for usage in the CB 27-band.
So go ahead big boy. Give me your best shot and try to shoot me down any way you can. I ain't no rookie to CB radios.

Shooting you down is what you do to yourself with some of the comments you make. I notice you haven't defended the silly response you made to me the other day. I quote:

"Technicians can not get more power out of it simply by tweaking. The power out you do get is in the audio, not the RF." I have never read a statement more ridiculous by someone who claims to be knowledgeable about CBs.

Here's a good question for you. How many feet of coax do I need if my antenna is 32 feet from the transmitter?



Standard wisdom says you need multiples of 18', so for 32' you'd need 36' of coax.
However,

1. The frequency of CB signal is 27.4 MHz (somewhere around the middle of the CB band).

2. The wavelength (in feet) of our CB signal is 36 feet.

3. A half wavelength is 18' and a quarter wavelength is 9' (or 108").

4. The CB signal is an RF sine wave, which rises above and drops below a zero reference point once each full cycle.

You should recognize most of these numbers.....especially the 108" value, which just happens to the the length of the 108" steel whip antenna, made very popular during the CB craze of the late '60s. And don't forget that 18' is a half wavelength for our CB signal.

The other concept that must be understood is that when radio signals travel through coaxial cable, they slow down a bit. They no longer can travel at the speed of light as they do when traveling through the air. How much they slow down is determined by the type of coaxial cable being used. So that RF engineers and technicians can accurately determine cable lengths when doing radio related work, the manufacturers provide a value that is know as velocity factor, or VF for short. The VF is used as a "correction factor" and is applied to the cable measurement so that the person building the cable assembly can physically determine the length based on the unique properties of the coaxial cable being used. This is important because wavelength is dependent on the frequency of our radio signal so it changes as does the frequency. VF for a perfect cable is a 1.0, and since we have no perfect cables in the world, the VF is always less than 1. The cables commonly used for CB applications have a VF range from about .6 to .8 or there abouts. RG58U is the most popular; it has a factor of .66, so let's use that.

Multiply that "perfect" 18' by the velocity factor of .66, you get... 11' 9" as a more realistic "perfect" coax length. But this is all BS anyway. The effect of coax length on CB signal is miniscule, so small as to be immeasurable except by very expensive equipment that few CB techs will own.

So, to answer your question, Richard, use any length of cable you want. Since it's unlikely you'll find cb cable packaged in 32' lengths, you're back to using 36'--or two spliced 18' cables.
BTW, the imperfect connection between two cable lengths will itself degrade your signal.


This information comes from my own knowledge, greatly enhanced by the *Antenna Handbook*, one of the textbooks used by CB techs in training.



--
*fas-cism* (fash'iz'em) n. A system of government that exercises a dictatorship of the extreme right, typically through the merging of state and business leadership, together with belligerent nationalism. -- The American Heritage Dictionary, 1983
.

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