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 Post subject: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 5:11 am 
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Looking for information about synchronous detectors. I've done some searching but don't seem to have much luck. I'm not interested in products to purchase.

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 Post subject: Re: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 9:26 am 
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What do you want to know?


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 Post subject: Re: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 12:44 pm 
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I'm looking for something simple to build that gives better performance than an envelope or product detector. I found this, which uses a small portion of the AD607. That in itself, using about 20% of the device, seems a bit of a waste, but so be it. This IC is one of several developments for the ill fated am stereo of the 70's I guess it was, dam, slept since then.

Anyway this is the scheme, but I'm wondering if there are any later ICs dedicated to synchro detect specifically for HF comm applications.

Image

I suppose there are software iterations but I'm looking for hardware solutions. Actually I'm thinking about putting it into that SX-101 I'm working on. I want to make a minimum impact on the radio, as is.

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 Post subject: Re: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 1:09 pm 
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Actually the AD607 was developed for digital demodulation service. To quite the datasheet

Quote:
The I and Q demodulators provide in-phase and quadrature baseband outputs to interface with Analog Devices’ AD7013 (IS54, TETRA, MSAT) and AD7015 (GSM) baseband converters


The two parts of the chip that aren't used in WA1SOV's circuit above are the mixer and IF amp.

AFAIK there isn't an "all-in-one" sync detector chip. WA1SOV's is about as simple as it can get. There are other circuits using NE602s (ARRL and W3FJJ circuits) and the Motorola AM stereo chips (Communications Quarterly from 1992). There are some links here: http://user.netonecom.net/~swordman/Rad ... eRadio.htm

For your SX-101, you'll need a circuit that will handle the 50 KHz IF. I'd build it using a pair of NE602s as the I/Q demodulators, a 74HC4046 phase detector, and a LO that runs at 4X your IF frequency divided down by a 74HC74 johnson counter for the I/Q LO signals. That way your two LO phases are ALWAYS 90 degrees apart, no adjustment required and no phase drift to worry about, since changing the BFO frequcny a few KC +/- 50 KHZ is a significant percentage of the BFO, and I don't think an analog phase shifter would quite do it for you.


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 Post subject: Re: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 6:41 pm 
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Mike

If you can find a schematic for the Lowe SRX-100 communications receiver
it uses a simple quasi-sychronous AM detector circuit. I think it was a one
chip design, using a fairly common part (at the time.) I used one for a
very brief period some years back.

Pete

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 Post subject: Re: Synchronous Detector Information?
PostPosted: Jul Sun 17, 2011 7:07 pm 
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You can build a quasi-sync detector using a NE602 mixer and a LM311 comparator as a limiter to generate the carrier reference. Split the signal from the IF to both the mixer input of the NE602 and the input of the LM311, then feed the output of the LM311 to the LO input of the NE602. You'll hafta do some level matching, as the NE602 only wants ~500MV of LO signal. Output of the NE602 is yer audio output.


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