I'm hoping some of the list are familiar with the newer currently-available oscillators available from the distributors. Some background: I'm starting to play with a short-term 1PPS holdover application, mainly to cover up brief GPS signal loss events (a few minutes at most). Since I may at some point want to make numerous copies of this, I'd rather start with a new oscillator as opposed to digging through the junkbox or buying surplus. Lower cost (<$100 ideal, lower is even better) and power consumption is good. My short-term stability requirements indicate to me that I'm probably looking for an OCXO instead of a TCXO, although it looks like some of the best TCXO's out there are in the range which will work in most cases (50ppb over temperature (or better)). I suspect I'm going to handle the holdover in a FPGA. As such, I don't think I'm going to bother trying to voltage control the oscillator. Seems like it will make the overall circuit simpler and I don't have to worry about a whole bunch of control circuit temperature compensation. I've dug through enough datasheets at this point, my eyes are glazing over. I also know that the spec sheets are only part of the story when it comes to oscillators. I also have found over the years that often the part I'm looking for (that 20ppb Temperature-stable TCXO for a reasonable price) exists if you know the vendor to look at... So any specific recommendations or pointers toward a brand/type would be appreciated. -- - Forrest

On Donnerstag, 24. September 2020 02:20:50 CEST Forrest Christian (List Account) wrote: > I'm hoping some of the list are familiar with the newer currently-available > oscillators available from the distributors. Not really familiar, but I've been looking for a small 5V 10MHz OCXO myself and found this one on Digikey: https://www.digikey.de/product-detail/de/taitien/NA-10M-2503/1664-1014-ND/ 6126536 With a +/-3ppb rating on temperature stability it doesn't look too shabby on paper at least. I have not used it yet, so cannot really "recommend" it, but it is one of the few options that you can simply buy from DigiKey without breaking the bank. This one cost me around 90€ (taxes included). Regards, Matthias

Hi > On Sep 23, 2020, at 8:20 PM, Forrest Christian (List Account) <lists@packetflux.com> wrote: > > I'm hoping some of the list are familiar with the newer currently-available > oscillators available from the distributors. > > Some background: > > I'm starting to play with a short-term 1PPS holdover application, mainly to > cover up brief GPS signal loss events (a few minutes at most). Is “a few minutes” < 10? I’m guessing it is. > > Since I may at some point want to make numerous copies of this, I'd rather > start with a new oscillator as opposed to digging through the junkbox or > buying surplus. Lower cost (<$100 ideal, lower is even better) and power > consumption is good. My short-term stability requirements indicate to me > that I'm probably looking for an OCXO instead of a TCXO, although it looks > like some of the best TCXO's out there are in the range which will work in > most cases (50ppb over temperature (or better)). What is your holdover requirement in ns ? If 10 minutes is the max number, that’s 600 seconds. 1 ppb average error would be 600 ns. Is this to much? > > I suspect I'm going to handle the holdover in a FPGA. As such, I don't > think I'm going to bother trying to voltage control the oscillator. Seems > like it will make the overall circuit simpler and I don't have to worry > about a whole bunch of control circuit temperature compensation. Without knowing the holdover requirement there’s no way to really guess if this makes sense. A 2 ppm TCXO that costs < $1 can be steered with a $2 DAC. Steering it to < 0.1 ppb is not super crazy. To get 0.1 ppb out of a “static” device you would need a Rb rather than an OCXO. > > I've dug through enough datasheets at this point, my eyes are glazing > over. I also know that the spec sheets are only part of the story when it > comes to oscillators. I also have found over the years that often the part > I'm looking for (that 20ppb Temperature-stable TCXO for a reasonable price) > exists if you know the vendor to look at... > > So any specific recommendations or pointers toward a brand/type would be > appreciated. > Steer a TCXO …. Bob > -- > - Forrest > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.

I accidentally only replied to an off-list reply with the following information. It was also meant to go to the entire list: Let me clarify here a bit: The application is: 1) In an unconditioned/semi-conditioned space. The ambient temperature can slew 20*C easily over the holdover period. (Think sun hitting an outdoor enclosure first thing in the morning - the ambient temperature tends to rise quickly). The overall temperature range is -40 to +60C, although those edges are rarely hit, and usually only when fans/heaters fail (more typical is 0-50C). 2) I need to stay within a 'few' microseconds of UTC alignment. No it isn't specced better than that. 4-5 uS is probably a good target. However, 10uS is probably ok and 30uS has been shown to not cause a lot of problems. Beyond that things get bad fairly quickly. Nominal 1PPS UTC is coming from a GPS receiver. The application is ok with a uS or so of cycle-to-cycle jitter. 3) 10 minutes would be a good target. Longer is better, like in any holdover. My basic math has been: 5 uS over 10 Minutes is ~8ppb. (5uS/600). If I can tolerate worst-case of 30uS, then I can get away with 50ppb. The implementation idea today is to clock a FPGA with an appropriately stable clock, then do either a 1Hz PLL or some other similar arrangement in the FPGA designed to track the GPS 1PPS when it's operational, or switch to holdover when it's not. I don't particularly see a good reason to discipline the oscillator when I can effectively measure it's frequency in the FPGA - If I know the measured frequency of the oscillator is 10.0000033425 Mhz, I can output the 1PPS every 10000003.3425 cycles, with each 1PPS aligned to the next clock edge. The jitter introduced by this method isn't going to be a problem in this application. Or put differently: I'm not steering the oscillator, I'm steering the divider in the FPGA. So my spec when I get right down to it is that I could tolerate a clock source which is fine with a worst-case drift of 50ppb over 20*C, but I would be more comfortable with something close to 10ppb. I note that Abracom and probably others make TCXO's which are rated at 50ppb over their entire temperature range, and the charts show that I probably can expect better than that over almost any given fairly narrow temperature range - and the lower power and ease of use are very much plusses. But, they cost more than an low-end OCXO. The main disadvantage of the OCXO's is the higher power needs. And my tendency to say 'well, I've already got a OCXO in the circuit, maybe we should go up to the expensive parts... I apologize for the softness of the specs here and (even worse) in my original message. Right now I'm sort of just playing with the 'is this doable for a reasonable cost, and what are the cost/benefit tradeoffs' game. And trying to get something I can play with and throw into the "environmental chamber" (aka converted old freezer) for testing. On Wed, Sep 23, 2020 at 6:20 PM Forrest Christian (List Account) < lists@packetflux.com> wrote: > I'm hoping some of the list are familiar with the newer > currently-available oscillators available from the distributors. > > Some background: > > I'm starting to play with a short-term 1PPS holdover application, mainly > to cover up brief GPS signal loss events (a few minutes at most). > > Since I may at some point want to make numerous copies of this, I'd rather > start with a new oscillator as opposed to digging through the junkbox or > buying surplus. Lower cost (<$100 ideal, lower is even better) and power > consumption is good. My short-term stability requirements indicate to me > that I'm probably looking for an OCXO instead of a TCXO, although it looks > like some of the best TCXO's out there are in the range which will work in > most cases (50ppb over temperature (or better)). > > I suspect I'm going to handle the holdover in a FPGA. As such, I don't > think I'm going to bother trying to voltage control the oscillator. Seems > like it will make the overall circuit simpler and I don't have to worry > about a whole bunch of control circuit temperature compensation. > > I've dug through enough datasheets at this point, my eyes are glazing > over. I also know that the spec sheets are only part of the story when it > comes to oscillators. I also have found over the years that often the part > I'm looking for (that 20ppb Temperature-stable TCXO for a reasonable price) > exists if you know the vendor to look at... > > So any specific recommendations or pointers toward a brand/type would be > appreciated. > > -- > - Forrest > -- - Forrest