[UK-CONTEST] Cables

[Tony Roskilly]

Hi All,

One aspect that hasn't been mentioned is cost,  unless you have very deep 
pockets, Heliax and even some of the more classy coax can soon get 
horrendously expensive.

I have do my radio on a very tight shoestring indeed and it has forced me to 
experiment with various versions of twin feeder.   After a lot of fiddling 
around, I now use homebrew twin,  the wire is domestic mains multistrand 
cable,  (less than a tenner for 100M) and insulators made from narrow bore 
white water pipe, which costs about a tenner for enough to make a lot of 
feeder with spacing of about 3 feet between insulators.  This material may 
not be perfect and I'm sure there are others out there that are have better 
RF propeties but it is cheap and easily avialable.  I use a spacing of 4 
inches, merely because that seems to be a reasonable comprimise between 
losses when ice and snow covered and making the feeder less manageable to 
use.   I have also used this configuration for the elements of my 80M folded 
dipole with great success.

Unless my antenna theory from College days back in the late 60s is wrong, 
the actual impedance of open wire feeder shouldn't matter than much unless 
you are feeding an antenna of the same characteristic impedance from a 
source with the same output impedance so I'd say go for a reasonable 
distance between the wires and use cheap and cheerful insulated multistrand 
domestic wire which is available just about anywhere.

I heartily endorse the comments about the black "450 Ohm" stuff,  a) it gets 
lossy in the wet b) the stuff I bought had copperweld type wire which goes 
rusty should anything nick the insulation c) its very expensive compared to 
superior home-brewed twin.
The 300 Ohm slotted stuff isn't much good and of course the 300 Ohm solid is 
only good for holding up plants in the garden.

Can confirm re very long open wire feeder runs at commercial and government 
stations, the old HF point to point station at Somerton had very long open 
wire runs, at Portishead Radio RX site (prior to remoting from Somerton) all 
but the vertical dipoles which were close to the building, were run on open 
wires, a Govt station I worked at had some Rhombics with literally over a 
mile of twin feeder.    I would guestimate the impedance of the twin feeder 
at these stations to be 600 to 800 Ohms, but I was on the operating side not 
the tech so it is a guestimate.

Vy 73
  Tony G3ZRJ