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

Werner Kullmann, HB9BNK hb9bnk at uska.ch
Wed Apr 27 06:41:31 PDT 2011

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 

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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