On 4/16/2011 12:21 PM, Les Kalmus wrote:
> Walt,
>
> Having done just that, here is what I did:
>
> I have an Ameritron RCS-8V remote 5 port antenna switch at the support
> point for one of the Beverages.
> The other beverage termination is connected to this switch through a run
> of direct burial RG-6.
> Unused ports on this switch are not grounded.
Having read often that common mode rejection and isolation are so very
important in getting the most out of Beverages I share my experiences:
I have found here that the performance of a reversible Beverage improves
when the unused port is terminated (75 ohms) improving F/B and noise
from unwanted directions if that is the case. I gave up on Ameritron
RCS units for RX antenna switching since there is no provision for
easily doing the proper termination. I also learned the hard way that
sending voltages and having switching diodes and having relays reduced
reliability from enhancing electrolysis (here in the tropics and close
to the sea) to zillions of ants for some reason being attracted by
voltage (don't know why) but I have had failures in two DXE boxes
because of them alone. Trust me they deposit all kinds of crud all over
the PC board they enjoy living on.
Because good RG-6 is not that expensive I always run a separate
feedline for each port (direction) and make them exactly 1/2 wave length
electrical (determined by their velocity factory) into the shack and
into a surplus (eBay) Dynair video switcher (got them in either PL-259
or BNC variety). The nice thing about these surplus switchers is that
*all* unused ports are terminated (until switched on) with internal 75
ohm resistors. I am assuming that this termination is reflected or
repeated back at the antenna itself. I test the configuration by
removing the unused feedline from the box on BC band signals off the
back of the active two wire Beverage with a significant improvement in
rejection of signals in the reverse direction. This method seems to
make the overall performance better and for me was an easy way to get
away from all the problems associated with switching voltages, stuck
relays, corrosion, power supplies, and insects.
The Dynair video switch has over 75 db of isolation, is totally passive,
but the locking push buttons make an audible snap which is a slight
distraction.
Herb, KV4FZ
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