At 06:33 PM 12/07/2002 +0000, you wrote:
K4KYV wrote:
>(3) All the rf transformers he shows are autotransformers, grounded at one
>point, with a tap for the coax feedline. With any antenna of this kind,
>including the K6STI loop, the flag, ewe, etc., the recommendation is always
>to use a transformer with separate primary and secondary and
>electrostatically shielded if possible, with the bottom end of transformer
>secondary strapped to the coax shield but NOT grounded to the same point as
>the primary. The purpose of this configuration is to avoid common mode
>noise pickup. These three questionable items make everything else in the
>book suspect, even though at first glance most of it appears to be based on
>sound principles.
>
VK6VZ replied:
G'day Don and all,
As many have already written on this reflector, Beverages are not an exact
science. Length is everything and the other stuff - what type of matching
transformer, common mode chokes - are usually far less importance in my
experience.
The autotransformer type of matching transformer has always worked great
for me and there has never ever been a problem with noise pickup due to
common mode currents, even though I live in a semi-rural (semi-urban) area.
My way has always been to do the easiest possible thing - autotransformer,
no termination, one single quarter wave radial running directly underneath
the Beverage - and only worry about the other stuff if the antenna/feeder
picks up lots of noise.
My Beverages have always been too short (200 to 400' in length) and have
been very quiet, but only the longer ones have really been good for signal
pick-up (probably because there is less need for termination with longer
Bevs because they pick up more signal/are generally less critical).
One way of working out if your Beverage is really working is to tune across
the band during the CQ 160, or CQ WW CW. In its preferred direction, say
Europe, you will find a whole new layer of stations to work with the
Beverage, under the noise on your tx antenna.
Vy 73
Steve, VK6VZ
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