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

Dee morsesat at optonline.net
Wed Apr 27 07:25:00 PDT 2011

Since you are using a very good rig and adding a great preamp, to hear what
you are after and expense involved might be as simple as adjusting the gain
(SP2000 indicates it is adjustable and already has a helical front end) so
as to stop this interference.  Doing this simple thing might correct
everything--Let us know if it works.  I adjusted the gain of my preamp to
stop similar type intermod.
Dee, NB2F 

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Werner Kullmann, HB9BNK
Sent: Wednesday, April 27, 2011 9:42 AM
To: amsat-bb at amsat.org
Subject: [amsat-bb] searching advice on low hpass filter for 146 MHz

To improve the reception of  the sats on 145.9xx MHz with my little yagi, I
recently acquired a SSB-preamplifier SP-2000. To my dismay, the reception on
my IC910H was intermittend heavily distorted.

After a while I found, that a nearby located commercial transmitter (POCSAG)
emitting bursts on 147.300 is so strong, that the frontend of the IC910H (or
its AGC) practically quites the receiver on 145.900.  When the bursts stop,
reception resumes. 
Difficult to qso.

I have experimented with a large cavity filter and found, that the impact of
the bursts can be reduced, so that normal satellite work is possible again.

Now I am looking for advice on how to build a steep low pass filter,
eliminating everything above 146 MHz, to be mounted before the preamp on the
mast. The filter must however be capable to accept the rf power, if I work
in V/U mode.

Thank you for any ideas !

Werner, HB9BNK
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