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

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Subject: TopBand: BCB qrm es shunt fed tower etc.....
From: broz@csn.net (John Brosnahan)
Date: Sun, 01 Dec 1996 14:06:38 -0600
At 11:48 PM 11/30/96 -0400, you 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 ?


I'd suggest that the problem is an overload problem in your receiver.  The
receiver is generating the offending signals through IMD.  The inv-L antenna
is just fed directly into the RX without any matching and carries the BCB 
signals at full strength--enough to overload the RX.  On the other hand the 
shunt fed tower is matched for 160 but poorly matched for the BCB--thereby 
reducing the strength of the BCB signals and their tendenency to generate
distrotion products in your RX.

Suggest you use matching on the inv-L for its filtering capability or just use
additional filtering on your RX system to reduce the overload.

I have a similar problem with matching 40M Yagis with the MFJ, or the AEA
SWR units.  A local BCB station overloads the SWR measurment and
provides for AM modulation (on the MFJ).  Adding a shorted 1/4 wave
stub does not change the 40M SWR but attenuates the BCB signals enough
to eliminate their tendency to overload.

Hope this helps.

73  John

John Brosnahan
La Salle Research Corp.
24115 County Road 40
La Salle, CO 80645 USA

voice 970-284-6602
fax   970-284-0979
email broz@csn.net


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