"Stuart Longland VK4MSL" wrote in message
...

Well, I've been doing some further thinking on this idea of a homebrew
set. Gareth pointed me to the "minima" homebrew set:

http://www.phonestack.com/farhan/minima.html

I must say, that thing is truly inspiring. It got me thinking though.



Always my problem, an excess of thinking, a paucity of getting on with it
:-)




I'd like to reach up into the VHF; 2m if possible. Now I bought some
Si570 ICs the other day, and they're quite capable of reaching 160MHz.
So 144MHz is no problem. Taking the 3rd harmonic should get me to 70cm.

10.7 MHz is pretty standard for both*****, and there are helical cavity
filters for 145MHz,
as used in the "Simple Spectrum Analyser" design (G4PMK, Nov 1989 RadCom)
Nor sure about 70cms, but there might be SAW filters, as used for the 433.92
domestic products.

Failing that. a cavity filter or interdigital filter, is a possibility.The
most
professional design around is probably Scotty Sprowls's spectrum analyser
(http://scottyspectrumanalyzer.com) and that uses a cavity filter for a
1.3GHz if,
with the second IF being 10.7 MHZ.

BUT BUT BUT as emphasized above, these are thoughts and not experiences!


***** I've a scrap main board from an FT780 which is a 70com rig but it uses
IFs
of 56MHz, 10.7MHz and 455kHz