[TowerTalk] Balanced Line using Coax ?

Jim Lux jimlux at earthlink.net
Wed Jul 30 10:54:31 EDT 2003


At 11:42 AM 7/30/2003 -0400, you wrote:
>I am wondering what the impedance would be if two RG8X coax cables are 
>right alongside each other...

100 ohms.. 2 * 50 (or 104 if RG-8X is 52 ohms.. it's probably not 
controlled that well anyway)


>this would be easy to fabricate... either some tape or heat shrink every 
>few feet would make a clean/neat bundle..

They actually make coax "zip cord".  I don't recall the number, and it 
might be more expensive than 2 RG-8X's, because the RG-8X, etc. are sold in 
huge volumes. (Alpha 9845 is dual RG 59-B/U for instance) There's also some 
funky dual 93 ohm stuff for networking (based on RG 62).  Again, I 
don't  recall the numbers

There's a RG-63B/u which is 125 ohm, a pair for 250 ohms..(0.5 dB/100ft, 
compared to 0.66 for the RG-8 family, and 1.1 dB/100ft for the dual RG-59)


 From a fabrication standpoint, there are a number of wire and cable 
companies around that will be happy to gang up a bunch of coaxes in one 
jacket with appropriate filler material and so forth. It's not all that 
expensive ($<0.50/ft back in 1990), and the minimum orders are in the 100 
foot range.  They have fairly generic machines that do this.  (they can 
also hotstamp your name on the coax... be sure you get your coax back after 
field day... I worked for a company that had custom 12/3 extension cords 
with the company name on them so they'd get them back (eventually))  I'll 
look through my old notes to see if I can find the mfr.  (Standard Wire and 
Cable rings a bell, but that might not be it)




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