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

i8cvs domenico.i8cvs at tin.it
Tue May 3 15:36:22 PDT 2011

Hi Werner, HB9BNK

I have seen your measurement on spectrum analyser with and without the
passband cavity filter but the result is not satisfactory because you need
to add a notch cavity filter tuned to suck the - 20 dBm offending POCSAG
signal at 147.300 MHz

By the way you can solve the problem using a less know "Front End
Crystal Antenna Filter"

The above filter is a passband filter to be placed between the antenna
and the preamplifier input and it's passband is very sharp and narrow
and only flat for about 30 KHz after that the responce belove and upper
the passband drops down for about -60 to -70 dB

For example you can order a passband from 145.925 to 145.955 MHz
or from 145.955 to 145.975 MHz to work  OSCAR-7

You can install the filter inside the SSB Electronics preamplifier  between
the input coax relay and the gate of the GaAsFET and this allow you to
transmit in 2 meters because on transmit the crystal filter is swithed OFF
from the TX line.

Alternatively you can place the crystal filter at the antenna but outside
the preamplifier on a PCB into a separate box with two coax relays in
order to switch OFF the filter with the purpose to transmit and to receive
the full 2 meters band.

There are many manufacturers as you can see on Google searching with
"Front End Crystal Antenna Filters" but they must be ordered on request
and specifications of the customer and I believe that it is a difficult task
to get only one prototype.

In your situation I suggest you to call by telephone Mr Barkoviak at
the SSB Electronic factory because he know many crystal manufacturers
in Germany and I am sure he can order the filter for you under your

I know Mr Barkoviak very well and he has ordered many not standard
crystals for me to be used into my SSB Electronics converters and

In additions I am confident that Mr Barkoviac will be interested to
know the results of your experimentation using his SSB Electronic

Best 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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