[Premium-Rx] Homebrew Demods

[Bob Betts]

Barry:
It sounds like an interesting project, particularly the filter selection aspect of it. The current project on my bench uses a 10 MHz upconverter which allows the use of a receiver as a tuner, and where the 455 KHz can then be fed to a second receiver at 10.455 MHz (an area where the radio easily meets its best specs). This allows for the use of a radio with a nice front end along with one that has favorable filter selections.
So far, the testing has been super! I've used a Racal and Watkins-Johnson in various configurations along with a few SDR receivers. The combination of added sensitivity, dynamic range and selectivity are amazing. Added noise doesn't seem to be an issue. The unit I'm building will control everything except the actual tuning, so there will be minimal knob twiddling. The second radio can be "set and forget".
 
Keep us posted on you project -- I like the concept.
 
Bob, N1KPR
 
Bob,

Very interesting project.  I am working on something that has a few things in common.

I bought a Sherwood Synch Detector a few years ago in rack mount version.  I built a switchbox for the input.  I used a cast aluminum box and mechanical 4 pole 4 position switch to select the input.  The box has BNC inputs and output,  The IF feeds from the source to a 5K ohm pot, this allows me to adjust the IF level fed to the detector.  Adjust the lowest input IF level to match the detector and reduce the level using the pots for the other inputs.  Un-selected inputs are grounded at the switch.  I was able to fit this on the 3 1/2" rack panel.  On the other side of the detector I plan to add an audio switch system.  Rob Sherwood had the panel painted an ugly flat gray color.  Using either your idea or the sign idea, I can letter the switches and cover the upgly paint job.

There was an interesting synch detector in QST 10 or more years ago.  The circuit used MV2105 and MV2109 VVCs with NE-602 and NE-604 ICs.  I bought enough pieces to build a half dozen or so of them.  Rob's circuit uses a longer time constant and needs to be 'guided" to near lock, but will hold lock for a very long time.  He also has an audio amp with high cut and low cut or boost.  The QST circuit was designed to feed back to the radio's audio system.  In lock mode it does a great job on AM, unlock and you can manually adjust the BFO for SSB and CW.  Neither Rob's system or the QST circuit has any IF filtering.  I have a couple of KIWA modules that I am thinking of adding to the circuit, 16 KHz is the widest and 6,2 is the narrowest.  I though about adding these after the incoming switch box in another box to get 6.2, 9.0, and 16 KHz selections for bandwidth.  I might even add a 2.8 KHz and .5 KHz with simple 455 KHz amps to allow better
 performance on CW and SSB for the old receivers (HROs etc).

Thanks for the neat project!

73,
Barry



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