In a message dated 97-02-25 17:34:32 EST, km1h@juno.com writes:
<< All good information but certainly not in the realm of the popular press.
Maybe Tom would like to share the FULL design info, including the
transformers. Then we would all have a chance to build and evaluate.
I and others have been using the 12" to 18" spacing as recommended in
those pubs you have to pay money for. If I can trade in my runs of #12
Copperweld for some cheap 450 Ohm ladder line, I certainly want to hear
about it.
>>
You sure can Carl. I traded my homebrew wide spaced line in years ago,hi.
I agree Beverages are simple, forgiving antennas as a general rule.
But look at what the two wire reversable system is. The line acts a single
thick conductor that actually receives the signal, and a two wire balanced
(unless you make the Beverage out of coax) transmission line that allows
you to "connect" to the far end from the feedpoint.
While the Beverage itself is non-critical, the transnission line is perhaps
one wave long and in the air. The only thing that stops the line (when used
as
a transmission line) from picking up unwanted signals is the balance of the
system. If one conductor is closer to ground over the entire length of the
line it unbalances the system. That was likely ON4UN's worry.
Unfortunately, there is no way to guarantee any result. The best shot is to
use
a recipe that eliminates as many potential problems as possible.
The closer the wire spacing of the line, the less critical installation
related
unbalance this becomes. The higher the line, the less unbalance unequal
coupling to earth creates.
There is no reason in the world to have the conductors a large distance
apart.
My guess is that was done because pre-fabricated line was not available at
that
time.
I can't draw a transformer or system on e-mail, but I can describe what I
use.
I use a stack of five FB-73-801 beads (Fair-rite products 2673000801) wound
with a two pass low Z and five pass secondary #26 winding for the 450 ohm to
75 ohm transformer. Use a six pass secondary for 50 ohm systems. DO NOT
twist the windings in pairs, keep them as isolated as possible. Do not tie
the
primary feedline
For the reflection and source end transformers I use four turn transformers,
with one winding center tapped. Use the standard hookup with the source
end connections connected to a terminating resistor or the matching
transformer.
These transformers are pretty flat from a few hundred kHz to over 30 MHz,
and have low (because few turns are used) stray capacitance.
I buy these beads by the hundreds, and use them in all sorts of MW and HF
broadband low power transformers.
73 Tom
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