Perhaps you were referring to a comment I had about the BOG. The twisted
pair is good because (1) you can use rugged military field telephone wire
that is usually availbable quite cheaply - check on ebay, and (2) it is
amenable to checking that the wires aren't broken by a simple Ohmeter check
at one end (if you short out the far end), and (3) if one of the two wires
breaks, you still get the same performance because of the unbroken wire.
Regarding length, termination, etc. - the usual techniques for the above
ground beverage apply. Just be aware that a shorter wire will work like a
longer one. How much? I don't remember exactly what I used, and since it
depends upon your ground characteristics, the best thing is to just try it -
it's simple enough. Because my ground was very rocky, it was not possible
to use ground rods. So, for grounding, I used a quarter wave radial that
zigzagged back and forth in front of the long antenna conductor(s) and at
right angles to them. This zigzagging also had the added benefit of
reducing signal pickup on the grounding radial. It helped fit it all into a
shorter length, thereby allowing a longer antenna conductor too. When
terminating the BOG I've used 200 Ohm resistors for terminating the main
conductor to the radial. One comment though, my East BOG is unterminated,
and it has excellent F/B ratio - about 20 dB or more. I'm not sure, but
perhaps this is due to the increased losses being on the ground. The usual
source material usually indicates only about a 3 dB advantage for the
unterminated Beverage in the opposite direction (i.e. from the unterminated
end towards the feed point). Apparently, for my soil conditions at least,
good F/B ratio results from an unterminated antenna. Perhaps this is due to
some unique combination of length and ground characteristics. I'm not
really sure, and some experimentation would be needed to pin this down.
I've fed all of these antennas using a simple 4:1 impedancance transformer
wound on a small toroidal core. The "ground" side of the cores were
connected again to zigzagging 1/4 wave radials. One concern I have about
your plans for using a utility easement is that it sounds like it would be
parallel to power lines and close to them - resulting in potentially
disastrous noise pickup that would negate the BOG's usually fine S/N
characteristics. Please let us know how this works out for you.
73,
Riki
K7NJ - 4X4NJ
-----Original Message-----
From: topband-bounces@contesting.com
[mailto:topband-bounces@contesting.com]On Behalf Of Nelson Moyer
Sent: Friday, October 22, 2004 4:17 PM
To: topband@contesting.com
Subject: Topband: Twisted pair BOG?
I week or so ago an Israeli ham mentioned using a twisted pair BOB on 160
meters. I did a reconnaissance mission down the utility easement in my
neighborhood and I think I could get away with an on the ground receive
antenna. Please, contact me off line with the details of length,
termination, grounding, etc. Thanks.
Nelson, KU0A
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|