[TowerTalk] 75 or 70 Ohm twinlead or ladderline cable - does it exist?

[Jim Brown]

On 3/25/2014 9:31 AM, Tom Osborne wrote:
> I remember good old 'twisted pair' that we used 'back in the day.' I 
> had a Heathkit AT-1 and just bend one wire and stuck it inside the 
> coax jack and taped the other wire to the outside of the coax jack.
>
> Who knew about PL-259's and SWR back then :-)  Think the twisted pair 
> was about 75 ohms. 

Hi Tom,

Twisted pair is great stuff, and far better at RF than most folks 
realize. I'd guess Zo to be between 50 and 75 ohms, which makes it a 
decent match to a dipole. Virtually all of the loss in transmission line 
below VHF is due to copper loss, so big copper means low loss, and a 
good twist minimizes both radiation and pickup on the feedline from 
differential mode current. A good choke is still required to kill common 
mode current.

73, Jim K9YC