Electronics > Metrology

Homebrew GSPDO Questions

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Wallace Gasiewicz:
ED;

I cannot find the equation, but isn't there an equation for caps and resistance in a filter for 1/2 wave power supplies???
Also one involving a big inductor?
Could this be the sort of same thing?

Wally

edpalmer42:
See!  I told you my brain was starting to shut down!  Instead of 'loop equation', I probably should have said 'loop response'.  Yes, there are equations for power supply filters and they are basically similar to what you're doing here.  If you really want to get into it, there are many books and articles on PLLs and their design and construction.

A couple that I know of are "Design of phase-locked loop circuits, with experiments" by Berlin and "Phaselock Techniques" by Gardner.  Gardner is pretty heavy but Berlin is intended for hobbyists.

Articles and web pages are almost too numerous to mention, but here are a few:
Brooks Shera's original article that started the DIY GPSDO era - https://www.qsl.net/n9zia/wireless/QST_GPS.pdf
James Miller's design that yours is based on - http://www.jrmiller.online/projects/ministd/frqstd0.htm
There are a bunch of Arduino updates for Shera's design.  Just search for <"brooks shera" gpsdo>

Wallace Gasiewicz:
Ed:

I looked again at the schematic and I see what you are talking about. I noticed that myself when I built the thing. I donno why the EFC comes off the loop filter where it does rather than at the other point where the 22K resistor and 20 uF cap are joined. I just built it and didn't question the original plan.
Perhaps it is designed this way to keep the 20 uF cap from discharging too rapidly, otherwise another resistor would have to be employed between the EFC of the Oscillator and the 20 uF Cap to keep the cap slowly discharging???

Wally

thinkfat:
Simulate it, play with the values. LTspice is free.

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