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

[Michael Tope]

On 3/24/2014 11:27 AM, William Hein wrote:
> Looking for info on 75 or 70 twinlead or ladderline cable.  Does such a
> thing exist?
>
> Google search did not come up with anything but maybe I'm overlooking
> something
>
> Tnx
> BIll AA7XT
Spiderbeam uses insulated Wireman CQ-532 PE insulated multistrand copper 
coated steel for their elements:

http://www.spiderbeam.com/product_info.php?info=p197

At the feedpoint of several of the driven elements they bring wires from 
the two element halves together and run them in parallel for a short 
distance. The wires are held parallel by multiple short pieces of 
adhesive filled shrink tubing spaced an inch or so apart (see page 13):

http://www.pd7bz.com/radioprogs/antennes/spiderbeam_constructionguide_english.pdf

This parallel combination of CQ-532 is supposed to have a characteristic 
Zo of 50 ohms and I can attest from personal experience that it handles 
1500 watts with no problems at the moderate VSWRs that that Spiderbeam 
exhibits. You could probably get the Zo up 70 to 75 ohms by adding some 
shrink tubing around each individual piece of CQ-532 to increase the 
effective spacing. As with everything on their antennas, this Spiderbeam 
twinlead is very lightweight.

For longer runs where building the Spiderbeam type twinlead as described 
above is too cumbersome and weight is less of a consideration, you might 
look at running two pieces of RG-83 35 ohm coax in parallel. That would 
give you 70 ohms balanced Zo between the center conductors.

73, Mike W4EF..........