Low distortion AM radio detector

Circlotron · 15th March 2008, 10:06 AM

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 · 15th March 2008, 01:16 PM

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 · 17th March 2008, 10:13 AM

Yo! Thanks for that.

BrianL · 26th March 2008, 03:31 AM

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 · 26th March 2008, 05:46 AM

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

ratza · 26th March 2008, 09:27 AM

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

dangus · 27th March 2008, 07:02 AM

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...tWaveRadio.htm

oshifis · 27th March 2008, 01:02 PM

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.

15th March 2008, 10:06 AM	#1
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Low distortion AM radio detector 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. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

17th March 2008, 10:13 AM	#3
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Yo! Thanks for that. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

26th March 2008, 03:31 AM	#4
BrianL diyAudio Member Join Date: Mar 2002 Location: USA	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 __________________ bel

26th March 2008, 09:27 AM	#6
ratza diyAudio Member Join Date: Dec 2007 Location: Sibiu, Romania	http://sound.westhost.com/articles/am-radio.htm __________________ Any solution is a compromise.

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15th March 2008, 01:16 PM	#2
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	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.

26th March 2008, 05:46 AM	#5
jcx diyAudio Member Join Date: Feb 2003 Location: ..	direct conversion software radio with Mega-sample ADC and DSP chip?

27th March 2008, 07:02 AM	#7
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	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...tWaveRadio.htm

27th March 2008, 01:02 PM	#8
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	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.

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