Looking for guidance with radio design

The actual tuning circuit is not so big as the antenna. To which are you referring?

in article snipped-for-privacy@nospam.com, Fred Bloggs at snipped-for-privacy@nospam.com wrote on 2/5/06 9:16 AM:

A ferrite coil and 365 pf variable cap are typical parts.

Well- if small is what you want then block convert it upwards by x100 and then do the channel selection.

R-C anti-alias filter Fast ADC Single-Chip DDS. Audio Driver. Done.

PN2222A

But don't even think about battery operation and be prepared to shell out several times the dough that you'd pay for a nice AM radio.

If I had to do it I'd upconvert like Fred suggested, but not by 100 times. Somewhere to an IF where you can buy a cheap filter of less than a 100kHz BW. 10.7MHz would be really low cost and small here. Then downconvert to 455kHz and use the usual 455kHz stuff. Done :-)

Regards, Joerg

"Jon Yaeger"

If you use an external antenna, the RF stage can use the same mini size coils as the IF does - circa a 6 mm cube.

If you have NO antenna - you will get no reception !!

........ Phil

Use a varicap, or several in parallel, in place of the 365 pf variable capacitor. The ferrite coil is the antenna.. . the radio not gonna work to pretty good without it!!!!

What? Designing a radio isn't dangerous? GG

YAWN.....

"The Real Andy"

Or just getting over another MONSTER hangover ???

Or is it both ??

........ Phil

Do you want to use a magnetic (coil) antenna, or do you have a connector feed from somewhere else? ... like in a car.

Thanks

Frank Raffaeli

YAWN....

be

tuning

AM has lots of atmospheric noise and relatively strong signals. Maybe just use a couple of feet of wire and go straight into a mixer, having volts of dynamic range (eg ..4066 etc). Feed mixer with square wave local oscillator at AM frequency of interest. Filter and amplify the resulting audio. Most of this stuff can be done nowadays with standard opamps. john

OK, but why a square wave? I do not see the adavntage on a sysnusoidal one.

thanks

Leo

Think of it as a chopper, that samples the input at F times per second, with a 50% duty cycle. Another example would be a "Lock-In Amplifier" or "Synchronous Detector"

Draw a graph of your incoming modulated RF carrier, and chop it so that every other half-cycle doesn't exist - voila! Detected audio! :-) (once you get in sync, of course. :-) )

Hope This Helps! Rich

In article , John Jardine. wrote: [....]

You can make 3 balanced mixers out of a CD4053 at modest frequencies.

just

of

Indeed yes!. One useful earner, needed two long wave down converters and a switch to swap between them. Bingo! CD4053. Could not have asked for better capability, even if in custom Silicon. john