Low distortion AM radio detector

[Circlotron]

Can anyone point me toward some info on low distortion AM radio detectors? I imagine a high speed opamp with a diode in the feedback loop.

 

[jackinnj]

Here's a circuit from Bob Schenck -- uses a precision rectifier -- perhaps you would want to use a CFB opamp:

http://www.amwindow.org/tech/htm/alowdisdet.pdf

He goes through the maths.

 

[Circlotron]

Yo! Thanks for that.

 

[BrianL]

Perhaps you should also look at a Burr-Brown (aka TI) OPA698 "clamp amp". You can set one of the clamp voltages to zero and make essentially a half-wave rectifier. A couple of these and a few ancillary components and you have a full-wave rectifier. There are also other op-amp-based rectifier circuits

 

[jcx]

direct conversion software radio with Mega-sample ADC and DSP chip?

 

[ratza]

http://sound.westhost.com/articles/am-radio.htm

 

[dangus]

Read up on synchronous detectors. IIRC that's about the best AM demodulator around. The CQAM AM stereo decoder was basically a glorified synchronous detector. Some Chrysler car radios supported AM stereo (mid '80s to ?) and they should cost you very little from a wrecking yard or eBay.

http://users.hfx.eastlink.ca/~amstereo/amstereo.htm

The following page is a goldmine of info on synchronous detection:

http://users.netonecom.net/~swordman/Radio/ShortWaveRadio.htm

 

[lcsaszar]

Also worth considering a PLL oscillator tuned for the carrier and a double balanced mixer (ring DBM) with suitable diodes.

I think that is called synchronous detection.