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.

Hal
w4pmj

"Ian White, G3SEK" wrote in message
...
Hal Rosser wrote:
Have fun - use twin-lead 300-ohm or ladder-line 450ohm...
use a half-wave u-shape balun + a 1/4-wave stub on each end - and your
runs
can be pretty long without a lot of loss - or a lot of expense.


I'm afraid this is largely a myth from the Olden Days. Back then,
twin-lead was probably better than most types of coax that hams could
buy... but coax has improved, and twin-lead hasn't.

The myth has been overly influenced by a few measurements dating back to
the 1950s, made under ideal conditions that can't be achieved in real
installations.

The reality is that twin-lead is difficult to install, sensitive to
electrical disturbances, of very poor quality if it's also low-cost, and
*very* sensitive to getting wet. The higher in frequency you go, the
more each one of these things matters.

(Yes, I know there are a billion TV sets out there using twin-lead - but
that doesn't make it right. Most viewers in the USA have been
brainwashed to accept appalling standards of TV picture quality.)

Parallel-line can be excellent for power distribution and phasing
*within* a stacked array. I've used it on the moonbounce array at
432MHz, in a wet climate, but those were short, straight lines that are
self-supporting with mostly air insulation - a completely different
thing.



"Rob" wrote in message
m...
I am finally going to put up a VHF antenna for 2 meter and another
antenna
for 70 cm.

What is type of coax should I use? Rg213? Or will RG213 be too
lossy?

Recommendations please...

As many others have said, it depends how important low loss will be for
*your* particular application.

If a significant length is involved, and you're interested in weak
signals, then RG213 (full quality, no substitutes) should be your
minimum specification.

People in the USA can recommend specific brands that will be available
to you.



--
73 from Ian G3SEK
'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek


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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?

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

"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