On Tue, 2 Aug 2005 21:41:42 -0700, "greg knapp 5"
wrote:

Wow, then if I had 6" spacing, it would have to be 5 feet from the nearest
other feed line! With the three lines I want to bring in, that is a cross
pole of 10 feet! Wow...I better consider using my old 450 ohm window ladder
line with about 1.x inch spacing so I can get down to a reasonable spread!

This is really opening my eyes up to the logistics of running this type of
feedline...low loss, but definitely more expense, bother, etc. than running
a bunch of coax lines! It almost makes me want to put up resonant antennas
(like parallel dipoles, fed with a balun and coax...so much easier!). I'm
going to have to think this through some more.


I worked in HF radio stations briefly a long time ago, and the
practice there was, IIRC, two wire lines of 3mm HDC with 200mm spacing
so they were around 600 ohms 'ish. There were also some 4 wire lines
with similar spacing (in a box config). These lines were strung out on
pole routes with separation about double the wire spacing. I can't
remember now if there were periodic polarity reversals. These were at
rx only or tx only facilities, so receiver de-sense was not an issue.
Do you need full duplex?

Clearly, the closer the lines the higher crosstalk (coupling from one
line to another), and presumably, twisted lines will have lower
crosstalk (think about the cat5 etc data cables).

Don't forget, that the antennas at the far end are coupled, and
achieving crosstalk of -100dB might not materially improve the
solution!

A pole route carrying a number of lines is a pretty serious project
(installation and maintenance). I would also look around at remote
switching solutions or multiband antennas to see if you can minimise
the number of lines you need to string.


Owen
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