Interference filters

Marijan Miletic S56A at
Tue Jan 14 11:06:03 EST 1997

Hi Frank, as cq-contest reflector is quite slow these days, I paid more
attention to your RX bandpass filters and discovered that capacitor values for
C1/C7, C2/C6 & C3/C5 differ although they should be all the same in 50 Ohms
symetrical system!  How comes, OM?
73 de Mario, S56A, N1YU.

>From donovanf at (Frank Donovan)  Tue Jan 14 12:06:01 1997
From: donovanf at (Frank Donovan) (Frank Donovan)
Date: Tue, 14 Jan 1997 07:06:01 -0500 (EST)
Subject: Interference filters (fwd)
Message-ID: <Pine.OSF.3.95.970114070502.13572C-100000 at>

Hi Mario!
Yes, the capacitor values are unsymetrical, which results in unsymetrical
VSWR at each end of the filter. The filters were developed as a messy
compromise between design simplicity (mainly ease of alignment), VSWR
bandwidth, one dB and 3 dB loss bandwidth, ultimate attenuation at one
suboctave, and "acceptable" attentuation one octave higher in frequency...
It was an awkward compromise to execute in the pre-PC days of the early
1970s, but they do work as advertised!  Perhaps with today's real-time
interactive PC-based tools, a more elegant design could be created! 
donovanf at

>From rvhoeft at (Hoeft, Roger V)  Tue Jan 14 13:55:15 1997
From: rvhoeft at (Hoeft, Roger V) (Hoeft, Roger V)
Date: Tue, 14 Jan 1997 07:55:15 -0600
Subject: Elevated radials for inverted L - how high is good??
Message-ID: <c=US%a=_%p=INTERGRAPH%l=HQ1-970114135515Z-7050 at>

Hello all,

What do the experts out there say is the minimum effective height to
have radials elevated for a 160 inverted L.  I have the radials and feed
point about 8 - 9 feet off the ground, but all I seem to have
accomplished is RFing the TV through the cable and my sons' personal CD
players.  With the location of the L and my yard, I am not able to have
a good, well laid-out field of tuned radials for the L.

I've read about the big dawgs using elevated radials - I guess the real
question is what should I expect, performance wise, from having elevated
radials for the L?

As always, the assistance and information from the reflector is most
helpful and appreciated.  

Roger Hoeft
rvhoeft at

Amateur Radio is a contact sport

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