Narrowbandpass IF filter

[VE3GZB]

I think I've got a design that's going to work well. It's based on a Q multiplier modification meant ironically for the R1155 (I have an R1155, bought it over the summer at the Fergus hamfest from Sid Lipkowitz for $75).

http://www.vintageradio.me.uk/military/qimpr1155.htm

I've cobbled something together on my bench and fed it a test signal. I'm able to trim the bandwidth down to +/-300Hz on 455kHz.

(EDIT: Bandwidth is -6dB +/-300Hz. I didn't mention that)

I'm using an old Messiner tube radio IF transformer as the heart of this Q multiplier.

I have more testing to do to see how well it will be, and then if it proves to be as good as I hope it will be, I'll modify the KW2000B, I'll install this IF transformer and a dual triode in place of the japanese mechanical filter, wire and tune it up and see how it goes.

I was contemplating using a transistor (a FET) instead of a tube....simplifying things so they can all fit inside the same metal can....but being not quite sure what voltage levels a transistor might meet inside that rig, I opted for the tube design instead.

73s
geo

[WA1GFZ]

Or you could spend $12 and buy a softrock kit and do it in software a lot easier. Also you will have a nice spectrum display

[VE3GZB]

Believe it or not, I absolutely HATE computers. I think computers will be the downfall of mankind.

And if it were up to me all of the computers in the world would be fired into outer space to burn up in the sun.

Have a nice day!

73s
geo

[W2VW]

Thanks for quoting bandwidth specs properly.

[VE3GZB]

No worries. I realized it when I was at work, got to thinking about it, checked my post during a break and realized my OOPS!

73s
geo