At 08:53 AM 10/23/96 -0700, you wrote:
>
>The RG-59 thread has been interesting...and leads me to a further
>question...why not use cheap 300-ohm TV twin-lead? It even matches at
>the Beverage end. Seems like stray pick-up would be marginal, loss
>minimal, and you only have to keep it away from other lines and metal
>stuff before transforming it to 50-ohm/unbalanced somewhere in the
>vicinity of the shack.
>
>73, Ward N0AX
Because it can't be buried or even laid on the ground. The imbalance
caused by close proximity of other conductors (ground) will imbalance
it enough to cause it to pick up signals that will distort the pattern of the
Beverage.
Even coax alone is sometimes used as a receiving antenna for low
noise pickup--demonstrating that braid-shielded wire will pick up signals,
even without an antenna. I would never consider using plain RG-58/59/213
for a Beverage feed. I would use a flexible coax if it had a foil shield
(100%) as well as the braid like the CATV stuff. I use old 1/2 inch CATV
hardline just to eliminate the chance of pickup through the shield.
Then you have to worry about currents coupling on the outside
and due to imbalances then coupling into the signal. Buried cable
is the very good--just laying on the ground helps--but the best approach is
to add RF chokes in the form of ferrite beads on the ends to only allow
coaxial currents to flow.
73 John
Bottom line: Just how much compromise can you afford--if going to the
trouble of installing Beverages isn't it worth the extra effort to get maximum
performance from them?
John Brosnahan W0UN
24115 County Road 40
La Salle, CO 80645
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