18' of coax??

Source;
http://www.arrl.org/


The length of the coax is determined by the length of the radio wave and the frequency of our radio signal. A full cb radio wave length is 36 feet, so ½ a wavelength is 18 foot. The cb radio signal is positive for ½ of the wavelength and negative for the other ½. At the ½ wavelength there is what is called a zero voltage point. This is where the signal is changing from a positive to negative or negative to a positive. The zero voltage point is at the half wavelength on every signal sent and received, this doesn’t change. The zero voltage point is where you want your coax to hook up the antenna. This is how the cb shops came up with the 18 foot length of coax. A lot of cb radio shops will tell you that you need to run an 18 foot long coax. Well I’m not a cb technician, I’m a driver, but I can tell you that they are not telling you the whole truth.
How do you correctly determine the coax length?
Multiply the wave length by the velocity factor of the type of coax that you are using. This will give you the proper coax length where any excess standing waves (SWRs) are visible to the SWR meter. This way you can have your antenna properly adjusted, and your cb working like it should.
What is a velocity factor?
The velocity factor is a term for how fast your signal moves through your coax. Your radio signal moves through the air at somewhere around the speed of light, but it doesn’t go through your coax at that speed. The velocity factor causes the signal to move through the coax much slower, which puts the length of coax needed to equal a ½ wavelength less than then 18 foot. The velocity factor needs to be accounted for when determining the length of your coax.
How do I find out what my velocity factor is?
The manufacturers will tell you the velocity factor. The velocity factor is known as the "correction factor". The perfect velocity factor for a coax is a 1.0, but there is no perfect coax. The velocity factors of Belden coax cables used by most cb shops are:

RG-58 velocity factor of .66 RG-58/U (foam) velocity factor of .79

RG-8A/U velocity factor of .66 RG-8/U (foam) velocity factor of .80

RG-213/U velocity factor of .66 9913 velocity factor of .84

By using this information you can find out what length of coax you really need. If you are using a mini 8 coax with the velocity factor of .66 you would need a coax of 11.88 feet long (142 and ½ inches). This is how got that length: 1/2 a wavelength (18 feet) x the velocity factor (.66) 18 x .66 = 11.88

So when you have a cb shop telling you to use an 18 foot coax, ask them WHY. Now you know the truth on coax lengths. You can get this and other information from the ARRL Antenna Handbook at http://www.arrl.org/

 

If you have the short shaft W2K's that dont get the "cone" above the cab,you'll need to correct that by getting the longer 10" shafts.
You cant get the whole cone above the cab due to length/height,getting about half will be sufficient.

 

Sorry but I don't buy into the dual wips ....Otherwise . velocity factor has to be used to make the coax part of this right .... and then you will have a directional antenna .... Check out about page 12 for what phaising antennas does.

http://www.hy-gain.com/man/pdf/AV-12AVQ.pdf

 

Not necessarily. I run my 5" shaft 2000 and have mine tuned to 1.2 flat across the band.

 

Shaft height has nothing to do with SWR tune-ability
You should know that already

As for the Co-phase set-ups their a futile venture with little return.
The link I posted was more for the understanding of the "theory" not that I agree nor disagree with their statements. I know what works out here and what doesn't.

 

now first let me tell you the fellow that told you the shorter the better on coax does not have a clue.
coax is a way to tune and match your antenna and the best way is to attatch an swr meter to your coax however if you dont happen to have a meter the recomended length is in fact 18 ft per antenna now that will keep your swr at or close to 1.1 to one witch will in turn insure that your radio is putting out at peak performance.
now i no that seems like a lot of coax but that is what you need for maximum performance. if that is not exceptabel you can buy tuneabel antennas and use a meter to adjust the antena to the lowest swr reading and they do make some good ones, now when your doing this rember you will not get an accurate reading with an amplifier in line or parked between two trucks or medal buildings the refection will throw your reading off.
an antenna makes the radio choose some good ones.
hope this has helped , good luck.-----southernpride

 

Take a look at these web sights, they will help explain it better.
Hope it helps.

http://www.signalengineering.com/ultimate/co_phasing.html
http://www.geocities.com/dtmcbride/hobbies/antennas_radio.html
http://www.bighairantennas.com/CBAntennas.html

 

18 foot per side????

The last time i heard is that you use 9 foot per side,not 18 ft. This is how i have run duel antennas since i started in 95 and it is the way i have been told to do so. Now when your setting the SWR you use one 18ft section. Set it on one antenna then the other. Then you install the co phased coax ( 9ft per side ) and your SWR should be right.

I could be wrong but i dont think the CB shop knows what they are talking about!




...But after a little research i find this....From Wilson's site.....

2. Type and length of coax cable to use:
If you are using less than 1000 watts, and a single antenna, use an 18' length of RG-58/AU. This cable is 95% shielded, stranded center, with 50 ohms impedance. If your power is less than 2000 watts, then change to the RG-8X type (also called Mini-8 or Super 8). For co-phased antennas with less than 1000 watts, use RG-59/AU. For power less than 2000 watts, use RG-11/AU. Both co-phasing cables should be 18' in length on each side.

http://www.wilsonantenna.com/swrt.htm


So after seeing that then i dont know which way to go. But like i said.Over the years i have always used 9ft to each antenna and never had a problem. Hell maybe I'm the one who does not know what he talking about?