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@uska.ch To: amsat-bb@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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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

http://www.kvg-gmbh.de/8.0.html?&L=3

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@uska.ch To: amsat-bb@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