CB COAX quesiton

PKP80

 
Joined
Nov 16, 2004
Messages
2,736
Location
Los Angeles, CA
I have 2 Coax cables that are running to the cb an 18 ft and a 9 foot. I need the two cables b/c of the fitting on their ends, but my question is this.

I want to cut the extra few feet of cable off each end of the cables. Is it acceptable to just buy a male coax head from radioshack and crimp it on the cut end? Will it affect my transmission?

Also, I've heard that the coax should always be in 3ft incriments b/c of how the waves travel. is this true? or can I just cut the wire down without being exact?

Thanks in advance,

Sam
 

BMAN

 
Joined
May 13, 2002
Messages
3,281
Location
Greg's place
AND


"Question: What is the "correct" length of coax?
Answer: The shortest length that makes it from the radio to the antenna.


Question: Are there any exceptions to the above rule?
Answer: 75 Ohm harnesses for Co-phasing is the only exception.


Question: Why do most mobile antenna makers recommend 18 feet of coax?
Answer: You got me, they claim you should use 1/2 wavelength multiples of coax. 18 feet isn't even close to being a 1/2 wavelength in any 50 Ohm coax you will find. Check some commonly used coax using the above formulas. RG-58, the most commonly used mobile antenna coax length would have to be 12 feet to be a 1/2 wavelength. RG-8X would need to be 14 feet.


Question: Ok, seriously nerd, when I trim my coax it changes my SWR. You can't tell me it's not good to lower my SWR from 1.5 to 1.2 by taking off a few extra feet of coax.
Answer: Hey, I'm not a nerd! Go ahead, change your coax length. If you change coax length and it affects your SWR in minute amounts, everything is working fine. If your SWR was 2.5:1 and putting in a 4 foot jumper brought it down to 1.3:1, this large change indicates you have real problems...i.e. common mode currents (see above). Really, you should be changing the antennas length to alter SWR. NO special length of 50 ohm coax is going to fix or lower your SWR signficantly and/or boost performance. Period."


Snipped right from the above link
 

Brentbba

Former Golfer
SILVER Star
 
 
Joined
Mar 27, 2003
Messages
10,349
Location
OC, CA
Great link Bman - I read the exact snips. Will be doing install over Turkey weekend myself. Timely question Sam!
 
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