Hi The chip is intended to be used with the divider engaged ( set to a divide of 2 or greater). That should act as a pretty good buffer if the layout is reasonable.
Looking at the spectrum analyzer plots, you either have crud on the control line ( ground it and see what happens … ) or on the supply. Either way it’s at audio frequencies. Your regulator may have issues (switchers are not what you feed a crystal oscillator with …..) or you need some caps in the 100’s of uf range on the regulator you have. Pay attention to the max output C even when running the divider. You can drive a scope probe, but not a 50 ohm line with the device. For 50 ohms you will need a pretty healthy ( = high current ) buffer. Bob > On Sep 18, 2021, at 12:38 AM, Julien Goodwin <[email protected]> > wrote: > > On 13/9/21 6:31 pm, Julien Goodwin wrote: >> https://www.microchip.com/en-us/product/PL500-16 (there's various other >> versions depending on the frequency you're after) >> >> Haven't seen any discussion about this on-list, but the PL500 is an >> easily (well, in normal times) available VCXO control chip, for those >> who might want to make their own disciplined oscillator, especially at >> less standard frequencies. I had some arrive today and put the board >> I've designed as an OCXO, and was able to trim +/- ~3kHz (around 26MHz >> nominal in my case, pretty much the expected +/- 150ppm), all really easily. >> >> I can't yet say much about quality as it turned out I'd put the wrong >> regulator footprint on the board, and with no local regulation the power >> rail was jumping all over the place, once I actually fix that and >> hopefully get it mounted in its intended enclosure for thermal control >> it'll be interesting how it goes (yes this was the project I was hoping >> to use my SR620 to monitor the other week). > > The thermal and shielding situation is to improve, but I did at least > get local regulation fixed, and while improved, it's still not great. > > With a 1mH inductor on the input (pre-regulator) and the local regulator > installed: > https://twitter.com/LapTop006/status/1439081534053515266 > > Traces are: > Yellow - Output signal (50-ohm terminated) > Green - Control voltage > Blue - 3.3v rail (main internal rail) > Red - 5v input rail > > At a rough guess I either need more bulk capacitance on the 3.3v rail, > or, more likely, lower impedance decoupling caps (I'm currently using > 100n 0603 of the "whatever I have in stock" variety). Would welcome > suggestions. I /do/ have an impedance analyzer that can handle this > frequency (goes to 500MHz), but I lack the SMD text fixture for it. > > I suspect an output buffer would really help too, and on its own might > significantly improve things. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
