"Pete KE9OA" ) writes:
I would go directly from 45MHz to 455kHz..............this is typical in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz
crystal used with the on-board oscillator allows you to derive your 2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator.
This is also a good system and it will give you fairly good strong signal
handling capability.

Pete

I'd hesitated to post since I wasn't sure of the sort of selectivity needed.

But yes, if the selectivity is available at 455KHz, there's no need to
have something in between that and 45MHz (or for that matter, if the
right selectivity can be had higher, gain is the only reason for going down
to 455KHz.

Old cellphones, the big and bulky kind, have IFs in the above 30MHz range
(the exact frequency has varied, but I think the majority of those that I've
stripped have had 45MHz IFs. And they tend to drop down to 455KHz after
that, meaning a scrap cellphone (the older the better because they
are cheaper and the parts are bigger) will generally provide a "roofing
filter" and the crystal to get down to 455KHz from there, and even the
455KHz filter if it doesn't have to be narrow.

Michael VE2BVW

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

"RST Engineering" wrote in message
...
I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to
either 21.4 or 10.7...there are cheap crystal filters at both
frequencies.

Jim


In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!