"ungvichian" wrote in message
oups.com...
I would like to be able to build, from scratch, an radio receiver for
AM Stereo and FM Stereo. I only have a rough idea of what I need (I DO
need a C-QUAM for example, a MC13028), and I have next to no experience
with electronics (just an electronics lab class, and some education on
computer-programmed boards, during university), so I have no idea where
to start (although I would be able to solder the thing together once I
knew what I had to do). I do know, however, what I want in my
theoretical receiver: a small size that I can carry around, 2 speakers
for stereo output, knob tuning like a regular analog dial radio (i.e.,
with a small arrow on a horizontal dial pointing out the frequency),
and possibly the ability to run off batteries or mains (220V 50Hz) as
well as a jack for outputting to headphones (or a computer for
airchecking purposes ). And of course, no old-fashioned tech like
tubes .

There's a pretty daunting undertaking for someone with your background. Are
you looking just to *buid* such a receiver or do you want to learn how to
*design* such things and understand exactly how they're working?

What's your budget look like?

You might want to start with something like
http://www.esssales.com/elenco/radio-kit.html and then start hacking the IFs
to go to your stereo decoders.

I know Chris Cuff has been known to make them, but who knows where he's
been these last few years? (Okay, he did have a few reviews at Amazon
as late as last year... and I just emailed him a few hours ago, but who
knows if he still checks his inbox?)

My impression has been that (1) Chris has probably just gotten busy with the
rest of his life over the past few years and (2) he's probably gotten
everything he ever wanted to out of C-QUAM. He was still selling PCBs on eBay
a few months ago -- I seem to recall reading that he said the response was so
great he was going to get more PCBs made (his initial auction was for clearing
out the last boards he had).

Besides, I've seen his radios at
sites on AM Stereo, and the tuning he uses doesn't exactly lend well to
sensitive tuning (with the frequencies written right on the knob).

I think you're confusing "sensitivity" with "precision." If you're looking
for precision tuning, unless you want to spend a lot of money, you should just
get a PLL-tuner radio. As for sensitivity, as with FM stereo, AM stereo was
really intended to work only when large signals (well, SNRs) were present, and
therefore Chris's add-on boards never needed to worry about sensitivity too
much.

I think you're pursuing a worthwhile project here (you'll learn a lot in the
process), but if you're looking to do something a little more up-to-date you
might consider doing an AM/FM stereo with a low-power DSP for the stereo
decoding. No MC13028 ICs, no FM decoders, etc. -- just digitize at IF and do
the rest digitally. You might buy a cheap commercial AM/FM stereo like the
old Sony SRF-42 (shows up on eBay regularly, and usually the prices are sane)
and then compare the performance of the DSP-based implementation with the
analog implementation. (The cool thing about decoding C-QUAM in analog is
that you have to build an analog divider -- definitely not the kind of circuit
you see every day!)

---Joel Kolstad