Re: [time-nuts] Freq cal to 1ppm without GPSDO
Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. Years ago, I remember smiling when I figured out that I could calibrate the clock in a scope. Just trigger on a PPS signal, dial out the delay to about 1 second, then see where the next PPS signal actually is. (The scope was off about 6 ppm.) -- 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] Freq cal to 1ppm without GPSDO
John, Besides the M12 receiver you will need an interface board to provide a 3.3 volt regulator for the M12, a 5 volt regulator and some 74c04's or some such to provide the 1pps interface and drive levels to a MAX232 chip for a RS232 interface. Then you will need to build up the Brooke Shera comparator and control board to interface a high quality oscillator in order to duplicate what is already provided in the Trimble Thunderbolt GPSDO. The Brooke Shera system gives you a part by part insight on what goes on in the Thunderbolt. However, there is a bit of work to get the Shera system up and running. The advantage of the Thunderbolt is that it is pretty much a plug-n-play unit. 73BillWB6BNQ John Beale wrote: Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. best regards, John Beale 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. ___ 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] Freq cal to 1ppm without GPSDO
John, One other thing I forgot to touch on. The 1pps signal out of the a GPS receiver is very jittery. For your TCXO it will be good enough except for you having to stare at the scope while comparing the GPS to your TCXO. Any oscillator of higher quality will be a problem when just using the GPS in the raw manner you are suggesting. 73BillWB6BNQ John Beale wrote: Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. best regards, John Beale 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. ___ 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] Freq cal to 1ppm without GPSDO
On Wed, Feb 16, 2011 at 11:43 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: Would you count these as nearer a working system? Only needs USB power, and includes the antenna and cable. http://www.sureelectronics.net/goods.php?id=99 I'm still waiting for mine to arrive. The advantage of the Oncore GPS is that it is well documented. Motorola wrote some detailed manuals in good English that are on-line. The Sure units are more ready to use but come with typical Chinese eBay documentation. Not saying which to get. Either should work. It's not hard to set up an Oncore GPS, just power it and interface it to RS232. the MAX232 chip makes that part easy and you can find DB9 connectors with the chip attached for about $4. But those Thunderbolt units are selling for $100 and are GPSDXOs with very good specs and only need power and an Antenna For many people the Antenna is that hardest part. You need a clear view of the sky and if it snows at your location some setup that keeps it clear of snow and then you need a cable from the Antenna back to the GPS. Running a wire out an open windows works for a test but not long term, Long tern you'd want a pole mount antenna up on the roof. So a few voltage regulators and interface chips is not much work compared to a permanent antenna setup One thing to look at when choosing a GPS is software. Maybe you are going to run an NTP server or you need software that runs on Linux. Or maybe you plan to buy several GPS receivers and want software that can run all of them. Always the old joke is true: A man who has one GPS knows what time it is, A man with two is never sure. So you buy three. -- = Chris Albertson Redondo Beach, California ___ 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] Freq cal to 1ppm without GPSDO
Hi There is another route to getting where you want to go. Buy an atomic clock. If you spend some time shopping, telcom rubidium atomic clocks are out there for sub $50 prices. For $100 you can get one quite quickly. An Efratom LPRO is one example. There are many others. They normally put out 10 MHz and some put out 1 pps. I'd avoid the 1 pps only versions for what you are trying to do. To be absolutely perfect, you do need to calibrate an Rb. I have never seen one that was off by more than 0.5 ppb (0.0005 ppm). Their tune range is rarely more than a few ppb. More or less - if they fire up and lock, they will do what you need to do. Of course if you have both the GPS *and* the Rb then you can calibrate the Rb against the GPS and get it real close. Welcome to time nuts Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of John Beale Sent: Thursday, February 17, 2011 1:10 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Freq cal to 1ppm without GPSDO Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. best regards, John Beale 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. ___ 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] Freq cal to 1ppm without GPSDO
John, I've had quite a bit of experience doing what you want to do, and have tried several methods. TV used to be a good way, but now that everything's gone digital that method is out. Despite advice to the contrary, comparing with WWV or similar on HF is NOT reliable to 1ppm. This is because there is Doppler on the short wave F-layer signal to the tune of several ppm. (It can be done if you are within ground wave or E layer range). An experienced user can achieve results with WWV by understanding when the propagation is E layer, and always using the same time of day. 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. 2. The reference oscillator in a GPS receiver isn't any help to you. While they need to be stable, they are NOT usually controlled by the GPS receiver. If you know what you are doing with the GPS NMEA 'clock bias' telemetry, you can work out what the receiver reference is doing, and compare with that, but that's only for experts. 3. If you want to divide the 10MHz down to 2Hz, you can run a 'Quartz' clock mechanism with second hand, and then, although this method is very slow, compare clock time with WWV's minute marks. A slip of 1 sec every two weeks is about 1ppm! Bear in mind that few TCXOs have a spec better than ±2ppm, and will often have other dynamic and hysteresis effects amounting to the same order. If you can find an OCXO to use as reference, so much the better. Method 1 is really simple to do and positively foolproof! 73, Murray ZL1BPU ___ 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] Freq cal to 1ppm without GPSDO
Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. best regards, John Beale 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. ___ 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] Freq cal to 1ppm without GPSDO
On Wed, Feb 16, 2011 at 10:09 PM, John Beale be...@bealecorner.com wrote: Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. Yes they sell for about $35 on EB. But you will need to build a support/interface for it. Yo will need some voltage regulators, a 74*04 inverter (the RS232 standard has DCD non-inverted but inverts data) TTL to RS232 level converters, 10-pin female headers and other misc parts. And a GPS antenna and cable. Also I think it uses an MCX connector for the antenna cable. You either have to get an MCX cable or replace the connector on the M12+ A just went through this process and can now blink a LED at 1Hz but as of yet not much else. Those Oncore GPS receivers are great but as shipped from Hong Kong they are just a bare receiver, not a working system. -- = Chris Albertson Redondo Beach, California ___ 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] Freq cal to 1ppm without GPSDO
Yes they sell for about $35 on EB. But you will need to build a support/interface for it. Yo will need some voltage regulators, a 74*04 inverter (the RS232 standard has DCD non-inverted but inverts data) TTL to RS232 level converters, 10-pin female headers and other misc parts. And a GPS antenna and cable. Also I think it uses an MCX connector for the antenna cable. You either have to get an MCX cable or replace the connector on the M12+ A just went through this process and can now blink a LED at 1Hz but as of yet not much else. Those Oncore GPS receivers are great but as shipped from Hong Kong they are just a bare receiver, not a working system. -- = Chris Albertson Redondo Beach, California Would you count these as nearer a working system? Only needs USB power, and includes the antenna and cable. http://www.sureelectronics.net/goods.php?id=99 I'm still waiting for mine to arrive. Cheers, David -- SatSignal software - quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
