RadioBanter - View Single Post

September 30th 05, 07:21 PM

wrote:
I've always wanted to build an SCA adapter for an FM radio so I
could see what else is available in the 88-108 MHz band. A web-
search found lots of schematics, but I'd appreciate suggestions
as to which schematic YOU have built that works.

I've built various 565-based units over the years. I only used the
schematics I found as starting points; the main one I used to start
from was the one included in the old, old 565 data sheets.

Make yours tunable, as SCA can range from 57 to 92 KHz and frequently
a station will have three different carriers with different material
on each. If I were doing one today, I'd use decent op amps as
high-pass for the input side and low-pass for the audio output,
instead of passive filtering. Especially at the output, I couldn't
put in enough stages to de-hash the sound without losing what little
high frequency output there is.

I might try a newer PLL as well. There was always something about the
565 that just seemed a little hinky and oversensitive to parameters.
I was never entirely satisfied with what I got, though some of them
worked pretty well considering all.

Don't be surprised if lots of what you find is digital signal.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.