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

Werner Kullmann, HB9BNK hb9bnk at uska.ch
Wed May 4 08:22:27 PDT 2011

Hi Domenico, I8CVS,

I am grateful that you took the time to look at my measurements 
und send me valuable advice. I have today sent our correnspondence 
to my contact person in SSB and keep you informed about their answers.

I will also study the diagram you attached, to understand, how you 
solved a similar problem.

This project is for me a great educational adventure !
We have a great hobby !

73 Werner, HB9BNK

Am 04.05.2011 00:36, schrieb i8cvs:
> 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
> specifications.
> 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
> transverters.
> In additions I am confident that Mr Barkoviac will be interested to
> know the results of your experimentation using his SSB Electronic
> preamplifier.
> 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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