Electronic Surplus Inc still has 72 ohm TX line. URL:

http://www.electronicsurplus.com/com...sp?category_id
=2170&czuid=1093172851680

Has Belden 8910

8210 BELDEN WIRE NEW TWINAX 72-OHM COAX CABLE 13 AWG POLYETHYLENE
PARRALLEL TRANSMISSION WIRE 10-FOOT MIN PURCHASE BROWN JACKET



Thanks to all who answered especially W1MCE who come up with the Belden
number -- the Google found the surplus site.
--
One Watt

To steal ideas from one person is plagiarism;
to steal from many is research.
-- Comedian Steven Wright

Micro MegaWatt wrote:
Thanks to all who answered especially W1MCE who come up with the Belden
number -- the Google found the surplus site.

Please allow me to point out that 75 ohm balanced line is not
much better than 75 ohm coax. The key to reducing losses at
HF is getting the Z0 as high as possible, i.e. the current as
low as possible. Last time I checked, there was no 600 ohm coax.
What's wrong with this picture?
--
73, Cecil http://www.qsl.net/w5dxp



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"
Thanks to all who answered especially W1MCE who come up with the Belden
number -- the Google found the surplus site.
--
One Watt

I may be in error, but I THINK if you use 4 equal lengths of 75-ohm coax
with the shields soldered together - and then make them 2 'pairs' of
conductors - you'll end up with a 75-ohm balanced line. (You don't use the
shield as transmission conductors).
If I'm in error, I hope someone will correct me on this.
Thanks
Hal


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It will be of interest that if the inner conductor of 600 ohm coax is 18
gauge wire then the outer conductor diameter will be 22,000 times greater.
ie., about 72 feet.

Not surprisingly, an 18-gauge wire at a height of 36 feet above ground has
an impedance of the same order. Isn't it reassuring to see how things all
fit nicely together.

Hal Rosser wrote:

I may be in error, but I THINK if you use 4 equal lengths of 75-ohm coax
with the shields soldered together - and then make them 2 'pairs' of
conductors - you'll end up with a 75-ohm balanced line. (You don't use the
shield as transmission conductors).
If I'm in error, I hope someone will correct me on this.
Thanks
Hal

Twinlead, ladder line, and other symmetrical lines are often called
"balanced" lines -- as you've done here. But it's important to realize
that there's nothing about these lines that causes the currents on the
lines to be equal and opposite (or "balanced"). Imbalanced currents
cause feedline radiation. Symmetrical lines can be unbalanced, and coax
can be balanced. To learn a little more about this, see "Baluns: What
They Do and How They Do It" in the _ARRL Antenna Compendium_, Vol. 1.

Roy Lewallen, W7EL

"Reg Edwards" wrote in message
...
It will be of interest that if the inner conductor of 600 ohm coax is 18
gauge wire then the outer conductor diameter will be 22,000 times greater.
ie., about 72 feet.


The connectors are going to cost a fortune!

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR

Dave VanHorn wrote:
"Reg Edwards" wrote in message
...

It will be of interest that if the inner conductor of 600 ohm coax is 18
gauge wire then the outer conductor diameter will be 22,000 times greater.
ie., about 72 feet.



The connectors are going to cost a fortune!

And then, think about soldering or crimping!! grin

Twinlead, ladder line, and other symmetrical lines are often called
"balanced" lines -- as you've done here. But it's important to realize
that there's nothing about these lines that causes the currents on the
lines to be equal and opposite (or "balanced"). Imbalanced currents
cause feedline radiation. Symmetrical lines can be unbalanced, and coax
can be balanced. To learn a little more about this, see "Baluns: What
They Do and How They Do It" in the _ARRL Antenna Compendium_, Vol. 1.

Roy Lewallen, W7EL

You are correct - as usual - so - if the transmission line (up to the point
of connection to that conglomeration) was carrying a balanced current (
equal in voltage and opposite in polarity at corresponding points ) - then
the aforementioned line could continue to assist with the migration of
electrons along the path of conductance in a balanced manner.
;-)
that's why a half-wave of coax can be used at a particular freq as a 4-to-1
balun - where the braid is 'left behind' but the current continues with the
voltage doubled - thus quadrupling the impedence matching ability... ...
and all that stuff



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