TopBand: BCB qrm es shunt fed tower etc.....

[John Mitchell]

At 11:48 PM 11/30/96 -0400, Mike Smith-VE9AA, Coreen Smith-Wynder Photo wrote:
>Can anyone explain why the BCB harmonics/qrm on my inverted L
>is (lets say)  S-8 on 1.830 , but on my shunt fed tower it's only 
>about S-1 ?

Hi Mike, et al

Can't explain it, but often wondered why my bevs pick up a strong "harmonic"
of a relatively close station on 610 kc, when my Inv L does not.  In fact,
the signal comes in strongest on one of the three bevs (NW).  I can reduce
it by about 12 db by using only 6db of attenuation.  Switching in 12 db
removes the signal completely (about 50 db down!).  Matching the antenna
using the built in antenna tuner (thereby achieving bandpass filtering)
removes even more of the offending signal.  That, together with the
non-linear action of the attenuator, leads me to conclude most of the
"harmonic" is a reaction by the rig, rather than any actual signal being there.

So, perhaps the harmonic is a result of overload of the fundamental into the
receiver?

73,
John K4IQ


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