On Tue, 11 Nov 1997 06:56:09 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>> From: Bill Hohnstein <k0ha@navix.net>
>
>Hi Bill,
>
>> modeling of a Beverage that I just put up today shows that chosing
>> a termination resistor for best F/B produces a 58 degree wide area
>> with a 20 dB minimum null range. My termination resistor chosen
>> shows a 65 degree wide area with a 20 dB minimum null range and the
>> four pattern nulls all having greater attenuation at their azimuths
>> than the similar nulls on the optimum F/B pattern.
>
>Any way we slice it, that is a 12% pattern null change that
>probably amount to a fraction of a dB directivity.
>
>In my experience, termination adjustmet changes null depth much more
>rapidly than null location. Is that what the models show? Since
>null depth *seems* to change much faster than null location, and any
>mistermination adds frequency sensitivity, I've always assumed the
>best termination to be a "flat" termination.
>
>73, Tom W8JI
Hi Tom and others,
About 12 years ago when experimenting with my first Slinky Beverage ( 4
over 120' ) I noticed the terminating resistance afforded very deep null
steering on 75M.
The tests were during daylight and with a 2.5K pot I could actually null
out individual stations in a roundtable. I mean deep nulls from S9+ into
the noise.
I suppose this was due to the improper xfmr and the antenna actuallly
being highly reactive and phase sensitive. This would probably not be the
case with a wire Beverage.
Has anyone experimented with or have suggestions to remotely vary the
termination resistance?
Carl KM1H
>
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>
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