[hpsdr] Synthesizers and sleepless nights

[FRANCIS CARCIA]

The Oleg design has a divider on the output and an additional divide by 2 in the mixer to generate two phases of lo drive to the mixer. 
  The VCO resonator is a hunk of transmission line. He could have used semi ridged but chose to make his own. This style oscillator is a notch down from a cavity if done correctly. A Mini Circuits part would be a lot easier. 
   
  I don't know if Drenta published any performance specs with his last article but the A/D 9858 at $45 could be used to duplicate his design. Still a VCO would be used.
   
  Either way I think the first thing to do would find a good prescaler and see how high it will go without spending a lot of bucks. Then add more divide by 2 stages until you get down to the band of interest. Each stage could also have an output to drive a front end of a different rang if desired. This would be like a modern HP8640B. 
   
  I have the latest Racal fractional N RM019B chip and I think it works well but I'm considering building a UHF oscillator and dividing it down to replace the one in the RA6830.
  I know a guy who has a bunch of them but might not be the way to go because it requires an external divide by n and phase detector. Oleg's design is a lot simpler.
  Signetics made a chip set years ago 4750 and 4751 but they are long gone. I built a receiver around them but never quite right at 1 HZ resolution. It was either over damped or noise. 
   
  Two kids and building a new QTH has me maxed out but glad to share 30 years of synthesizer data I've collected. gfz
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