"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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Hal Rosser wrote:

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.

The improvement clearly came from the extra antenna height. If you could
keep the extra feedline losses within reasonable limits, you were sure
to come out ahead on the deal.

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..

Fair enough. If the only other affordable way to get the feedline to the
top of that tree would have been 200ft+ of RG-fifty8 (at least 15dB book
loss), then direct twin-lead route definitely was the better choice.

I understand the limitations of twin-lead and ladder-line, etc - and
the fact that rain and other objects may reduce its effectiveness, etc

You do have the whole picture, Hal, and I respect that.

My problem is with the hams who only know half the story - the claimed
advantages. Somehow, it's always the warnings and limitations that get
lost... must be "selective fading".


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek