Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
On Nov 19, 2010, at 11:31 PM, Jim Lux wrote: On Nov 19, 2010, at 7:06 PM, Bob Camp li...@rtty.us wrote: Hi If high temperature is an issue, keeping the Rb cool will be a major chore. The OCXO will be far more happy at 75 than the Rb will be at 65. Depending on just how mobile we're talking about, the OCXO may have some issues with 2G tip / acceleration. There's a lot to consider in a setup like this and without a bit more data we're going to head off into crazy land pretty fast. Bob Crazy land? On time-nuts? Is there a difference? To some mobile is the chunk that goes down hole at the well site. To others it's (obviously) the crawler that heads down the gas line. I've even known people who seem to think it involves hopping in a car. I suggest a carefully balanced pendulum made of a Pt-Ir alloy driven by a water powered escapement. grin I was thinking of a nice super cooled chunk of sapphire . ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
Dave, Something is not making sense to me here. As GPS is generally available around the globe and obviously to your reference stations; how is it that the mobile will be able to find an area where the GPS is not available ? As to the mobile, if it is not going to utilize the GPS for a reference, you then need to determine the worst case error you can have over the course of time that the mobile is away from its GPS capability. That factor will dictate the kind of on-board reference you will need. It could be that a very good quality crystal oscillator will suffice. BillWB6BNQ Dave Jabson wrote: Greetings, I just discovered this mailing list, this is my first submission. Glad to find a group of folks who are into this kind of stuff! I'm working on an data acquisition application for my company that will require a very stable oscillator. Without going into too many specifics, there will be some reference stations spaced 100's of kilometers apart from each other and 1 mobile station that will be operated in an area where GPS is not available. I need to be able to collect data at all the stations and have the time synchronization be extremely good between the stations, including the one without GPS. For the reference stations it will be sufficient to have the timing of each one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA string and 1pps edge and all of the digital electronics will use the GPSDO 10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be done as needed. The mobile station can be synchronized to GPS initially to synchronize its clock as described above but will then have to rely on a free-running oscillator. The stability of this oscillator will dictate how much drift the mobile station's clock will experience relative to the reference stations. Keeping this drift as low as possible is my goal. I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave -- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
WB6BNQ wrote: Dave, Something is not making sense to me here. As GPS is generally available around the globe and obviously to your reference stations; how is it that the mobile will be able to find an area where the GPS is not available ? If GPS is jammed, you're in a high multipath area, or other reasons... Maybe the reference stations are above water, but your mobile unit is underwater during most of the data collection. Or if you're doing underground surveying.. not necesarily well logging, but say you're doing Electromagnetic surveys, I can think of lots of scenarios needing this.. As to the mobile, if it is not going to utilize the GPS for a reference, you then need to determine the worst case error you can have over the course of time that the mobile is away from its GPS capability. That factor will dictate the kind of on-board reference you will need. It could be that a very good quality crystal oscillator will suffice. Indeed.. if you're looking at times 24hrs, a good OCXO would probably do it. I'm working on an data acquisition application for my company that will require a very stable oscillator. Without going into too many specifics, there will be some reference stations spaced 100's of kilometers apart from each other and 1 mobile station that will be operated in an area where GPS is not available. I need to be able to collect data at all the stations and have the time synchronization be extremely good between the stations, including the one without GPS. For the reference stations it will be sufficient Sufficient meaning you need tens of nanoseconds sort of precision/accuracy? The mobile station can be synchronized to GPS initially to synchronize its clock as described above but will then have to rely on a free-running oscillator. The stability of this oscillator will dictate how much drift the mobile station's clock will experience relative to the reference stations. Keeping this drift as low as possible is my goal. How good does it have to be, and how long will you be out of touch... as low as possible is pretty darn low in this crowd.. Do you need 1 part in 1E13 over a week? Or 1 ppb over a day? (about 100 microseconds/day) Are you recording RF/Acoustic signals and need to be able to form coherent sums? I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Almost certainly... the advantage of an Rb is that you can turn it off, then turn it back on days later, and in a relatively short time, have decent absolute accuracy. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
jab...@quasarfs.com said: The mobile station can be synchronized to GPS initially to synchronize its clock as described above but will then have to rely on a free-running oscillator. The stability of this oscillator will dictate how much drift the mobile station's clock will experience relative to the reference stations. Keeping this drift as low as possible is my goal. Don't get hung up on the D idea. There are many very good single oven OCXOs out there. I think you will be much happier if you figure out how low a drift you need. I'm guessing you don't have a firm number because it interacts with other parts of the system and you are still designing that part. You need some rough numbers for sanity checking your options. Typical GPSDO boxes are good for a few microseconds over 24 hours of holdover. Is that within your ballpark? You can probably do much better than their spec sheet if your temperature is stable. Do you need one for a single experiment, or many for a production run? Do you need to prove it is good-enough from the spec sheets or can you try one in the lab, and run with it if it works? My suggestion would be to get a couple of good OCXOs, put them in the lab next to your Rb, and see how well they work. It's probably worth a few phone calls to see if the vendors have any data on 12 hour holdover. (But check the environmental conditions.) -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
Hi How much warmup time do you have before you go mobile? If the mobile unit can be kept hot before it heads out - the DOCXO wins. If it's a power up and roll in 10 minutes sort of thing, then the Rb is the only way to go. Bob On Nov 19, 2010, at 3:56 PM, Dave Jabson wrote: Greetings, I just discovered this mailing list, this is my first submission. Glad to find a group of folks who are into this kind of stuff! I'm working on an data acquisition application for my company that will require a very stable oscillator. Without going into too many specifics, there will be some reference stations spaced 100's of kilometers apart from each other and 1 mobile station that will be operated in an area where GPS is not available. I need to be able to collect data at all the stations and have the time synchronization be extremely good between the stations, including the one without GPS. For the reference stations it will be sufficient to have the timing of each one driven by a good GPSDO. Clocks will be sync'ed to UTC via the NMEA string and 1pps edge and all of the digital electronics will use the GPSDO 10MHz as their timebase. Periodic re-synchronization to the 1pps edge can be done as needed. The mobile station can be synchronized to GPS initially to synchronize its clock as described above but will then have to rely on a free-running oscillator. The stability of this oscillator will dictate how much drift the mobile station's clock will experience relative to the reference stations. Keeping this drift as low as possible is my goal. I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave -- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
Hello Dave, as some folks have already mentioned here, the best solution for you will depend on your specific requirements in terms of how much warmup time you have before GPS is gone, and how much drift your solution can handle. The PRS-10 is a good unit, but requires cooling, a large amount of power, only has a single 10MHz and 1PPS output, and it has a somewhat noisy output in terms of phase noise and short-term-stability. It also costs about $1500, is quite large, and does not provide a GPS receiver, nor one especially optimized for timing. You may want to look at the Fury or FireFly-IIA GPSDO units, these are lower cost, include the complete GPS sub-system, achieve performance similar to the PRS-10 after sufficient warmup, are much smaller, lower power, the FireFly-IIA has a built-in isolated distribution amplifier, and don't have an Rb lamp life limitation. Typical Fury DOCXO units can achieve better than 1us drift over 24 hours after they have fully stabilized, which is better than many Rubidium references. If you are looking for drift in the 10us range per day, you will need a double oven SC-cut OCXO. You didn't mention if your application was airborne, in that case you may need a low-g sensitivity oscillator to avoid loss of short term stability and increased phase noise due to aircraft vibration and acceleration. Rubidiums are especially sensitive to airborne vibration such as caused by Turboprops, Rotorcraft, etc. Without having your specifications for the warmup time, thermal changes, and the desired drift, it is difficult to say if a single oven, double oven, Cesium, or Rubidium based unit would work for you. Lastly, unless you are underwater or under-ground, GPS should be available with a modern, good jamming-resistant receiver, and if it is a modern GPSDO will perform as well or better than a modern Rb. bye, Said In a message dated 11/19/2010 14:43:43 Pacific Standard Time, li...@rtty.us writes: I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave -- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
Hi Dave, forgot to mention: The PRS-10 also has a limited temperature range only up to +65C, so military applications are a no-go. A good DOCXO will have +75C or even +85C capability. Also, the spec for the PRS-10 is 1.18E-012 per Degree C temperature change, and the units I mentioned before with the DOCXO are available in better than 2E-012 per Degree C over a wider temp range, so are very similar in performance over temperature. bye, Said In a message dated 11/19/2010 18:12:13 Pacific Standard Time, saidj...@aol.com writes: Hello Dave, as some folks have already mentioned here, the best solution for you will depend on your specific requirements in terms of how much warmup time you have before GPS is gone, and how much drift your solution can handle. The PRS-10 is a good unit, but requires cooling, a large amount of power, only has a single 10MHz and 1PPS output, and it has a somewhat noisy output in terms of phase noise and short-term-stability. It also costs about $1500, is quite large, and does not provide a GPS receiver, nor one especially optimized for timing. You may want to look at the Fury or FireFly-IIA GPSDO units, these are lower cost, include the complete GPS sub-system, achieve performance similar to the PRS-10 after sufficient warmup, are much smaller, lower power, the FireFly-IIA has a built-in isolated distribution amplifier, and don't have an Rb lamp life limitation. Typical Fury DOCXO units can achieve better than 1us drift over 24 hours after they have fully stabilized, which is better than many Rubidium references. If you are looking for drift in the 10us range per day, you will need a double oven SC-cut OCXO. You didn't mention if your application was airborne, in that case you may need a low-g sensitivity oscillator to avoid loss of short term stability and increased phase noise due to aircraft vibration and acceleration. Rubidiums are especially sensitive to airborne vibration such as caused by Turboprops, Rotorcraft, etc. Without having your specifications for the warmup time, thermal changes, and the desired drift, it is difficult to say if a single oven, double oven, Cesium, or Rubidium based unit would work for you. Lastly, unless you are underwater or under-ground, GPS should be available with a modern, good jamming-resistant receiver, and if it is a modern GPSDO will perform as well or better than a modern Rb. bye, Said In a message dated 11/19/2010 14:43:43 Pacific Standard Time, li...@rtty.us writes: I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave -- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
Hi If high temperature is an issue, keeping the Rb cool will be a major chore. The OCXO will be far more happy at 75 than the Rb will be at 65. Depending on just how mobile we're talking about, the OCXO may have some issues with 2G tip / acceleration. There's a lot to consider in a setup like this and without a bit more data we're going to head off into crazy land pretty fast. Bob On Nov 19, 2010, at 9:36 PM, saidj...@aol.com wrote: Hi Dave, forgot to mention: The PRS-10 also has a limited temperature range only up to +65C, so military applications are a no-go. A good DOCXO will have +75C or even +85C capability. Also, the spec for the PRS-10 is 1.18E-012 per Degree C temperature change, and the units I mentioned before with the DOCXO are available in better than 2E-012 per Degree C over a wider temp range, so are very similar in performance over temperature. bye, Said In a message dated 11/19/2010 18:12:13 Pacific Standard Time, saidj...@aol.com writes: Hello Dave, as some folks have already mentioned here, the best solution for you will depend on your specific requirements in terms of how much warmup time you have before GPS is gone, and how much drift your solution can handle. The PRS-10 is a good unit, but requires cooling, a large amount of power, only has a single 10MHz and 1PPS output, and it has a somewhat noisy output in terms of phase noise and short-term-stability. It also costs about $1500, is quite large, and does not provide a GPS receiver, nor one especially optimized for timing. You may want to look at the Fury or FireFly-IIA GPSDO units, these are lower cost, include the complete GPS sub-system, achieve performance similar to the PRS-10 after sufficient warmup, are much smaller, lower power, the FireFly-IIA has a built-in isolated distribution amplifier, and don't have an Rb lamp life limitation. Typical Fury DOCXO units can achieve better than 1us drift over 24 hours after they have fully stabilized, which is better than many Rubidium references. If you are looking for drift in the 10us range per day, you will need a double oven SC-cut OCXO. You didn't mention if your application was airborne, in that case you may need a low-g sensitivity oscillator to avoid loss of short term stability and increased phase noise due to aircraft vibration and acceleration. Rubidiums are especially sensitive to airborne vibration such as caused by Turboprops, Rotorcraft, etc. Without having your specifications for the warmup time, thermal changes, and the desired drift, it is difficult to say if a single oven, double oven, Cesium, or Rubidium based unit would work for you. Lastly, unless you are underwater or under-ground, GPS should be available with a modern, good jamming-resistant receiver, and if it is a modern GPSDO will perform as well or better than a modern Rb. bye, Said In a message dated 11/19/2010 14:43:43 Pacific Standard Time, li...@rtty.us writes: I had assumed that a Rubidium oscillator would give me the best stability over the course of 8-12 hours. Obviously a Cesium would be better but those are impractical due to cost and power constraints. I've begun evaluation of a Rb oscillator but now I'm being told by some people that a good DOCXO is likely to give me similar medium term stability (with obviously better short-term stability). Anyone here have thoughts on this? Obviously I'd rather go with a DOCXO for cost and power reasons if there's no performance benefit to be had using a Rb osc. The Rb unit I'm testing (http://www.thinksrs.com/products/PRS10.htm) seems to perform well but I am interested in hearing others' thoughts. Thanks, Dave -- Dave Jabson Systems Engineering Manager Quasar Federal Systems 5754 Pacific Center Blvd, Suite 203 San Diego, CA 92121 858-412-1706 www.quasarfs.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] DOCXO vs. Rubidium medium-term stability
On Nov 19, 2010, at 7:06 PM, Bob Camp li...@rtty.us wrote: Hi If high temperature is an issue, keeping the Rb cool will be a major chore. The OCXO will be far more happy at 75 than the Rb will be at 65. Depending on just how mobile we're talking about, the OCXO may have some issues with 2G tip / acceleration. There's a lot to consider in a setup like this and without a bit more data we're going to head off into crazy land pretty fast. Bob Crazy land? On time-nuts? I suggest a carefully balanced pendulum made of a Pt-Ir alloy driven by a water powered escapement. grin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
