Topband: 1 wire vs. 2 wire beverage?

[Garry & Yelena]

Will:

I use RG6 TV coax and therefore a 75 ohm system. RG6 is inexpensive, low loss
and lightweight--easily gathered up at the end of seasonal operation. The
mismatch at the RX is of no great consequence (SWR=1.4), but a transformer
can be added if you are fanatic about it. The RG6 uses F connectors, which
are cheap, solderless, and easy to install. Furthermore, the foil-plus-braid 
construction of RG6 ensures 100% braid coverage, and therefore little noise 
pickup in a long coax run. Grounding the feedline 10 or 20 meters before the
Bev is made easier by using common TV ground blocks.

I see no reason to run a double coax to a 2-wire Beverage, unless you plan
to combine both ports  in the shack with an LC circuit to make a Steerable
Wave Antenna (SWA). And I certainly see no reason to run coax to both ends,
especially if the coax runs the length of the Beverage to get to the far end.
Wind good transformers, and use relays to switch directions and terminations,
activated through the coax. It's not that big a deal to do it, and you do it
once.

I would avoid using a preamp unless your system losses (flat loss of the 
Beverage plus cable and transformer losses) are really excessive; at the
least, don't use any more gain than you have to.. A Beverage is broadband
--over at least one or two octaves--and the sum of loud AM B/C stations,
coastal LF/MF/HF stations, etc. can add up to the better part of a volt at
the preamp input. I was stunned to tune around below the B/C band and find 
60-over-9 signals!. Your broadband preamp could generate some very
interesting intermod products under those conditions, unless you also used
a preselector. Most lowbanders are aware that SNR--not signal strength--is
the issue on topband.


Garry, NI6T



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