Scroll way down past illustration.3 and you'll find coax lenght explained.

http://www.signalengineering.com/ult...ax_basics.html

 

I've used RG6 with no problems

 

Why would you use RG-6/U coax? RG-6/U is a 72 ohm coax. It also has a solid center conductor.

kc0iv

 

I think we are talking CB installations here, not satellite tv!:lol:

 

Some things to consider in antenna installation!

1) The antenna should be selected as such, so it can be mounted in a vertical or near vertical positions! Not anteater style laying down at 45 degrees!

2) Antenna design - coil position!
Of all the designs suggested and available, all the coil positions have been discussed!

a) Base Loaded - not practical in most truck applications, since it is near impossible to locate the coil above the roof line of the truck!

b) Mid-Coil - i.e. Wilson Trucker style, to be effective, 75% of the coil needs to be above the roofline, or in the case of fiberglass trucks, above the structural steel portion of the cab.

c) Top-coil - i.e. Firestick, Cobra, Francis or K40 Fiberglass whips - by all practicality, the best for most trucks and mirror mounted configurations! As the coil is at the top of the antenna and easiest to mount in an optimal configuration. Can also be purchased from 3 foot to 5 foot lengths, and most are easily tunable!

3) How many antenna, well, that depends on personal preference, availability of mounting locations, budget, and need to get out and touch someone!

a) Single antenna - the easiest and most economical to mount and set-up, and in most cases will yield good range results. RG-58 or Mini8) are exceptable in these situations, other types are stiffer and harder to use in a mobile set-up. Depending on the mounting location and grounding of the mount, will yield fair to optimal radiation patterns (i.e. front, back and side-to-side). Some trucks, such as Columbia's and Century Class will need a 12 guage or so wire run to the frame or other chassis ground, since the doors on these trucks do not yield good grounding through the mirror mounts.

b) Dual (co-phased) - little harder to properly set-up and match, also more expense. But in a tuned (i.e. boosted) radio, will yield much greater results, usually front to rear, side-to-side suffers a bit, but we need front and back more! Matched (co-phased) RG-59 is needed in this set-up for best SWR and lowest loss! (at least in a mobile set-up). Another note of interest - Properly set-up Dual (co-phased) antenna do not need a grounded mount. Thus, they work quite well in set-ups such as the T-2000 and Pete 387's. Although, grounded mounts do not hurt, and in some cases will extend the range and directional ability of the set-up.

c) Also, the best case scenario is the antenna be mounted 8 to 8'6" apart, any closer and they will need more playing around with to get a good SWR match, and a change in coax will be needed! I have mounted as close as 6', but needed to use RG-58 and a custom cophase connection! This set-up was very directional and not practical for daily trucking use!


Firestick has an excellent tutorial on their website, as well as other sources!

Safety! If you plan to push some amps! Get the coil away from you! Many do not realize the RF (radio frequency) burns! A high power linear pushing through a base or mid-loaded coil in close proximity to your arm or brain ( :?: ) can burn you and/or increase the risk or cancer! A friend of mine, had been driving for 20 plus years, loved his linear's, and quite often ran them cranked up! His custom antenna, much the same as the monkey-made and similar was mounted less than three feet from his head! He constantly had burns, similar to a sun-burn on his arms and forehead, also lost much of his hair! This man wore a cowboy hat at all times, except when in bed or in church, so the burns to his forehead were unexplained, until after his death!

He passed away 3 years ago from brain cancer, also had skin cancer on his left arm! After some research, and speculation, it was determined the cause of the cancer was his radio and linear!

You do not have to believe this story, since there are many articles and papers on the effect of high power RF to the body. A microwave oven is a RF generator - that is how it cooks food! Read the papers yourself! Part of the testing for an Amateur License is related to RF safety!

Anyhow, just supplying information, and not wanting to start the usual wars that occur regarding radios on this forum!

Good luck setting your rig up!

Another note: If you do not own an SWR/Power meter, get one! Not the $19.95 variety sold at the truck stop! You do not need a Bird! Radio Shack sells a good one for casual use, as well as some other outfits! Have noticed lately that the Pilot is carrying one, around $49, that looks very similar to the RS unit! Use it to match your antenna to your radio, and then occasionally, every other month or so (do not leave it connect full time), or if you notice a deterioration of your signal! Coax no matter how good it is, does break down over time. Antenna mounts may generate corrosion, thus loosing grounding or the little nylon washer between the antenna and the base mount will deteriorate and ground out the whip, causing your SWR's to go through the roof! Older trucks with worn door and corroded door hinges are also culprits of fluctuating readings!

 

Never used it for mobile use, but for base station with 1600w linear it works quite well.

 

Still don't understand why you would use 72 ohm coax for CB unless you are feeding a 1/2 dipole? Even then pretty hard to find balun for 72 ohm coax. Let alone finding connectors that will connect to the linear.

If you are using a rotating beam then solid core sure isn't going to last very long.

kc0iv

 

For all c.b/ antenna related questions you can find all u need at cbradiotalk.com