"Ian White, G3SEK" wrote in message
...
Hal Rosser wrote:
I've used it with success - recently. 450-ohm window-line (has
copper-clad steel conductors, so its tuff) then on each end: a
combination to match impedence - a 75-ohm 1/4-wave stub (goes from 50
to 112.5 ohm) then a half-wave u-bent setup (112.5 to 450 ohm) see page
165 of Antenna Compendium vol 6 for a better description - I wrote that
article back in 1999 or so. I've also used similar setups and 300-ohm
belden twinlead. It may be a myth from the olden days, but 2+2 still
equals 4 - just like the old days. And its not a myth - it really does
work.
What frequency? What length? What loss did you measure? Was it raining?
freq= 2m band
length = approx 200 ft (up and accross the yard to the top of a TALL TREE)
loss ---- what loss did you measure w/ rg58 (which would have been the
other affordable line)
ie: I did not "measure" it - but my signal reports from others were 'much
improved' over the same antenna on the roof.
Raining? - rain, shine, - didn't matter - the run was in free air... I ran
about 10 ft coax out of the house - then switched to twinlead - then back
again near the antenna..
a wives tale - probably so - but I still feel better after eating chicken
soup if I have a cold.
but dogone it - it was fun - I did it - I'm proud of it - and I'll probably
do it again. - It was a good exercise in matching impedences --- I was a new
ham, and wanted to experiment...
I used it because it was light weight and low-loss (per the specs in the
belden catalog) - I don't have the catalog in front of me - but to get the
same low-loss-ness I could not afford the hard-line. - and the weight of
that run would have prevented the setup I had in mind.
Plus - I used it as a weather instrument:
if it was wet - rain : it was was swaying - windy, etc.
I understand the limitations of twin-lead and ladder-line, etc - and the
fact that rain and other objects may reduce its effectiveness, etc - but
even if the loss was half as good, it still beat the best coax I could
afford.
Oh - and I used a tree rather than a tower to hold the antenna. - Trees are
kind of old-fashion too, compared with the modern towers.
Of course twin-lead can "work" in a wide range of applications.
The myth is that it can beat a modern coax cable at VHF, on a long run
with practical installation difficulties, and in the rain.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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