[amsat-bb] Re: searching advice on low pass filter for 146 MHz

i8cvs domenico.i8cvs at tin.it
Tue May 3 18:10:42 PDT 2011

Hi Werner, HB9BNK

In addition to my previous message I found that KVG in
Germany make "Frontend " crystal filters upon customer
specification in the range 100 to 200 MHz. The only problem
is that they are large and flat only +/- 7 KHz (14 KHz total)
and the insertion loss is 7 dB


Since the gain of the SSB preamplifier is about 20 dB you
can try to use the above filter for a test between the output
of the SSB preamplifier and the input of tranceiver IC 910H

In this configuration the gain of the preamplifier will be
reduced only by the filter insertion loss of 7 dB but having
available about 13 dB of preamplier gain the overall Noise
Figure of the receiving system will be not deteriorated. 

If all goes well and the preamplifier is not overload by the 
POCSAG 147.300 MHz signal you can order four crystal
filters to cover about 50 KHz to work OSCAR-7 

By the way I believe that the above crystal filters are very
costly and that two huge cavity one connected as passband
filter and the other one as notch filter is less expensive for
you and this is exactly what I did in my 2 meters receiver
system using both cavities after a high dinamic range Norton
type antenna mounted preamplifier to clean up the garbage
at 145.200 MHz in my location.   

73" de

i8CVS Domenico

----- Original Message -----
From: "Werner Kullmann, HB9BNK" <hb9bnk at uska.ch>
To: <amsat-bb at amsat.org>
Sent: Tuesday, May 03, 2011 12:10 PM
Subject: [amsat-bb] searching advice on low pass filter for 146 MHz

> I received several suggestions, when I stated my problem lasst
> week. While exercising, I started to document my 'case' and now I
> would be glad, if you could have a look at my measurements:
> http://www.hb9bnk.ch/index.php?id=59&L=1
> and let me have your opinion !
> I guess, that Domenico had the ultimate answer: two huge filters
> (if the problem can be solved at all) or Power-off of the
> preamplifier
> Thanks and
> 73 Werner, HB9BNK

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