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Old August 15th 08, 12:55 AM posted to rec.radio.shortwave
Dale Parfitt[_3_] Dale Parfitt[_3_] is offline
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First recorded activity by RadioBanter: Jan 2008
Posts: 141
Default 75 Ohms - It's Not Just For TV Anymore


"m II" wrote in message news:i62pk.7114$%b7.6611@edtnps82...
Dave wrote:

I've tried manipulating my twin lead cable into that configuration, to
no avail. The best I can get is something resembling a double helix. If
I leave it twisted like that, it may have genetic ramifications.

For parallel lines it's diameter v distance. Common zip cord is ca. 75
Ohms.


Now, I've always been led to believe that a ratio is a unit less
quantity. I get the feeling that some length of cable is needed here to
get an ohmic value. Perhaps something approaching infinity?


mike (easy as falling off a Log) II


Don't confuse DC Ohms with surge impedance of coaxial line- they have
nothing in common except their unit of measurement.
Speaker wire probably is a relatively low Z line- which then suffers from
two issues:

1.One reason typical amateur balanced line is low loss is because of the
high impedance.
2. The vinyl insulation of typical speaker wire is a lossy dielectric
compared to the polyethylene of balanced transmission lines. Look at the
tangent angle of vinyl vs. polyethylene or teflon.

Dale W4OP