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CB's 101 by Jeff Bergmann

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Offline Russ

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CB's 101 by Jeff Bergmann
« on: October 31, 2018, 08:13:40 PM »
CB's 101

As a federally licensed Ham radio operator of over 10 yrs i've come across a lot of folks who have the interest in getting their first radio....usually a CB. The unfortunate part is by and large companies who sell CB gear have no interest in teaching their customers the theory behind radio gear and many folks get upset really quick when their new radio just won't work the way they expect it to. I will cover a few things here that will hopefully guide you in the right direction if you plan on buying or already have a CB and you suspect it isn't operating at full capacity.

Every radio operates on frequencies. Frequencies have what are called wavelengths. Every single part or connection of a CB install is a mathmatical equation based on the wavelength of whatever frequency you plan to operate on. In this case its the 11 meter band.....the center of which is channel 20 or 27.205. Now.....the wavelenth of 27.205 is actually 36 ft tall. Now the important issue is the half of a wavelength....In this case its 18 ft. At 18 ft you reach the point where elecrically speaking the wave turns from a positive to a negative. This is the point where you want to connect a feedline aka your antenna coax. Now most people think you can just buy any old piece of coax cable and hook it up and it works right? NOOOO...it is a crucial part of the mathmatics that make radios work properly. You have to start at 18 ft. What makes things change is the particular coax you are using. There are many manufactures of coax and all have a little bit different characteristics. Every producer of coax lists on their websites what is called velocity factor. It is a relativity of the time and speed that signals pass down the coax. most velocity factors range from .66 to .79 to .80 etc.. So the math equation to find out exactly how long your coax needs to be is the velocity factor x18. so 18x .66 = 11.8 ft of coax. This will require you to be a litle creative on how and where to tuck the extra, but the most important thing is to coil it loose and keep it dry at all costs. The reason behind this whole thing is reflected signals and reflected power which will burn up the final amp section of your radio if the system is not in proper balance. A mismatch will cause power to return to the radio because it is not electrically balanced. This can happen quickly or over a long period of time, depending on how bad the set up is.

The other issues are clean power and grounding. Clean power is simply running directly to the battery or a fused power block supplied from the battery. NOT your main fuse block. You will get all kinds of interference from computers, alternators, lights etc.....bad power = noisy radio=bad reception.

Grounding is the other issue ESPECIALLY in Jeeps. The tailgate is probably the worst place to put a mount because the gate is totally insulated with weather stripping and secondly the only point of contact is the hinges which are ususlly greased which makes it more problematic. If you mount an antenna on a jeep gate, you have to run a seperate ground wire to the body. Behind the tail lights are some non painted metal surfaces to do this from.

Of course there is antenna tuning. Most antennas are built to operate within the band their built for, but some minor adjustment is always possible.  If you think your radio is FUBAR, gimme a holler and we'll get you all straightened out !!

Jeff Bergmann
KD8IYU
Russ

Offline Juggernaut

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Re: CB's 101 by Jeff Bergmann
« Reply #1 on: November 01, 2018, 02:31:50 PM »
 :popcorn:   







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