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).

On Mon, September 13, 2021 3:31 am, Julien Goodwin wrote: > https://www.microchip.com/en-us/product/PL500-16 ... > I've designed as an OCXO What temperature are you planning on running the oven? If that device is going inside the oven, watch the max operating ambient spec if 85 degrees. -- Chris Caudle

On 14/9/21 12:59 am, Chris Caudle wrote: > On Mon, September 13, 2021 3:31 am, Julien Goodwin wrote: >> https://www.microchip.com/en-us/product/PL500-16 > ... >> I've designed as an OCXO > > What temperature are you planning on running the oven? If that device is > going inside the oven, watch the max operating ambient spec if 85 degrees. > Yep. Sadly my use case includes "in an enclosure outdoors in the Australian summer" so I can't use a low temperature oven. This isn't something I'll be intending to sell or the 85c max would be uncomfortably close to operating, but everything else is 125c (or at least there's variants in the same package that are, my own stock is various things). Based on the datasheet I expect 125c would be just fine as long as thermals are actually managed, and if I pot the can with thermally conductive epoxy or similar it shouldn't be too bad. I have a temperature sensor on the board right next to that chip, however it's a *tiny* package (TI TMP117) and I've not actually managed to have one work after reflow.

On 9/13/21 7:36 PM, Julien Goodwin wrote: > > On 14/9/21 12:59 am, Chris Caudle wrote: >> On Mon, September 13, 2021 3:31 am, Julien Goodwin wrote: >>> https://www.microchip.com/en-us/product/PL500-16 >> ... >>> I've designed as an OCXO >> What temperature are you planning on running the oven? If that device is >> going inside the oven, watch the max operating ambient spec if 85 degrees. >> > Yep. Sadly my use case includes "in an enclosure outdoors in the > Australian summer" so I can't use a low temperature oven. You just need to move to Coober Pedy, and set your lab up in a dugout, which will keep things at a reasonable temperature. (Although, I must confess, I didn't meet anyone in Coober Pedy who claimed the advantages for time-nuts - maybe a marketing opportunity for the city?) otherwise, you're in the "design for 50C"  bucket, like us in SoCal.

On 14/9/21 1:42 pm, Lux, Jim wrote: > On 9/13/21 7:36 PM, Julien Goodwin wrote: >> >> On 14/9/21 12:59 am, Chris Caudle wrote: >>> On Mon, September 13, 2021 3:31 am, Julien Goodwin wrote: >>>> https://www.microchip.com/en-us/product/PL500-16 >>> ... >>>> I've designed as an OCXO >>> What temperature are you planning on running the oven?  If that >>> device is >>> going inside the oven, watch the max operating ambient spec if 85 >>> degrees. >>> >> Yep. Sadly my use case includes "in an enclosure outdoors in the >> Australian summer" so I can't use a low temperature oven. > > > > You just need to move to Coober Pedy, and set your lab up in a dugout, > which will keep things at a reasonable temperature. > (Although, I must confess, I didn't meet anyone in Coober Pedy who > claimed the advantages for time-nuts - maybe a marketing opportunity for > the city?) > > > > otherwise, you're in the "design for 50C"  bucket, like us in SoCal. 50c *ambient* though (and even here in Sydney we've hit 46c), in outdoor enclosures you can easily end up being 20c+ higher, even with ventilation. A bunch of friends of mine have worked for service providers here that used to run networking kit in such enclosures.

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.

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 <time-nuts@studio442.com.au> 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 -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there.

On 18/9/21 10:26 pm, Bob kb8tq wrote: > 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. I'm using the -17 variant, no divider, running at the 26MHz fundamental. > 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. First stage input is a Keysight N675xA supply, not the absolute quietest supply out there but plenty good enough (it's also currently the best I have, my last two linear supplies died, and I've not replaced them), the second stage is an MCP1802 LDO, now with 1mH on the input in series. I'd have expected 10uF to be enough bulk capacitance, but I can absolutely try chucking some more on and seeing if that does help. When I was just running the DAC without the oscillator the lines were dead quiet, I suppose it's also possible there's leakage from the control signal running too close to one of the lines to the crystal (just a hair under 1mm between the traces) > 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. It /should/ be able to handle driving into 50 ohms per the spec sheet, but I agree it's not doing a great job of it. >> On Sep 18, 2021, at 12:38 AM, Julien Goodwin <time-nuts@studio442.com.au> 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 -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com > To unsubscribe, go to and follow the instructions there. >

Hi > On Sep 18, 2021, at 9:12 AM, Julien Goodwin <time-nuts@studio442.com.au> wrote: > > > > On 18/9/21 10:26 pm, Bob kb8tq wrote: >> 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. > > I'm using the -17 variant, no divider, running at the 26MHz fundamental. > >> 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. > > First stage input is a Keysight N675xA supply, not the absolute quietest > supply out there but plenty good enough (it's also currently the best I > have, my last two linear supplies died, and I've not replaced them), the > second stage is an MCP1802 LDO, now with 1mH on the input in series. I'd > have expected 10uF to be enough bulk capacitance, but I can absolutely > try chucking some more on and seeing if that does help. You need a quiet linear regulator feeding the chip. Any switcher will drive it nuts. Indeed a lot of LDO’s are not very quiet. They also may be very poor at isolating you from switcher “crud”. You need to be careful about what you pick. > > When I was just running the DAC without the oscillator the lines were > dead quiet, I suppose it's also possible there's leakage from the > control signal running too close to one of the lines to the crystal > (just a hair under 1mm between the traces) > >> 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. > > It /should/ be able to handle driving into 50 ohms per the spec sheet, > but I agree it's not doing a great job of it. The spec sheet shows output current of 4 ma at full output and something in the 9 ma range with reduced output. You normally want to be at the < 4 ma point on a chip like this. 3V into 50 ohms gets you to 60 ma. The same loading issue can come in from a scope probe that has a bit too much C. A 12 pf probe is right at the edge / over in this case. Bob > >>> On Sep 18, 2021, at 12:38 AM, Julien Goodwin <time-nuts@studio442.com.au> 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 -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com >>> To unsubscribe, go to and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com >> To unsubscribe, go to and follow the instructions there. >>

On 9/18/21 7:38 AM, Bob kb8tq wrote: > > You need a quiet linear regulator feeding the chip. Any switcher will drive it nuts. > Indeed a lot of LDO’s are not very quiet. They also may be very poor at isolating > you from switcher “crud”. You need to be careful about what you pick. LT3042 and LT3045 are your friend here.  Excellent PSRR well up past 10 MHz. If you need more current, you can just parallel them. $6 each for the 3045 from Digikey