[R-390] External product detector

[Bob kb8tq]

Hi

There are a number of < $50 and some <$20 MCU boards that will make a fine SDR
for single frequency use. Yes, I realize this is heresy. If you are going to add solid state
stuff to an R-390 anyway …. why not do it the best way you can? IF comes out here, 
goes into board, audio comes out of board there, goes back into radio here …. for added
bonus points, AGC comes out of board there and goes back into radio over here. 

Bob

> On Sep 29, 2017, at 10:41 AM, Gordon Hayward <ghayward at uoguelph.ca> wrote:
> 
> I built an external product detector with 2 MC1496 mixers. The crystal BFOs are for USB, LSB and one exactly at 455 kHz for zero beating AM stations. The BFOs are fed to the two detectors in quadrature (90 degrees apart) which are fed to right and left channels. The stereo effect on the noise is remarkable.
> 
> 
> I also added a PLL FM detector and a precision diode detector for AM just because I could. I don't use them much. The box also includes a logarithmic voltmeter as a second S-meter for low signals.
> 
> 
> A third addition was a CL-90 thermistor to slow start the 390A.
> 
> 
> Cheers, Gord VE3EOS
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