Re: [time-nuts] Measuring frequency rather than tuning crystal
Here is a quote from the TF930/TF960 Service Guide, in the section on calibrating the internal TCXO: "Set the Measurement Time to 1s and repeat the process. The adjustment per step is now a decade smaller and multiple presses may be needed. The measurement restarts after each set of key presses. It will take a few seconds for the reading to stabilise because of the settling time of a filter on the control voltage. Aim to be within about 0.5Hz and then move to the next step." The reference to "the control voltage" strongly suggests that it is actually adjusting the timebase frequency via the frequency control input, not adjusting a numerical constant. We know that the TCXO is actually a VCTCXO, because it can be phase locked to an external reference. And we know it's actually phase locking the internal reference when an ext. ref. is supplied, not merely substituting the external reference in place of the internal one, because the manual says that the external reference must be a high-accuracy 10 MHz signal - it is not possible to use a different reference frequency. (There is more detail - see the "External Reference" section of the 930 or 960 manual). - Dave On Fri, Feb 27, 2015 at 4:23 PM, Dave Martindale wrote: > The TF930/960 does have a calibration procedure that is performed from the > front panel. Basically, you feed it a stable input from any known source > (so both 1 Hz and 10 MHz from a GPSDO should work) and then adjust until > the displayed frequency agrees with the known input frequency. The > resolution of this setting is quite a bit better than the stability of the > TCXO in the box. > > Now, this process could occur either by actually adjusting the frequency > of a VCTCXO in the box using a DAC, or by changing a calibration constant > stored in the memory of the device. I suspect it's actually the former, > because the instructions say that the adjustment path has a low-pass filter > that you need to allow to settle. This wouldn't be necessary if the > calibration simply changed a stored number. > > Dave > > > On 27/02/2015 15:08, Paul Alfille wrote: > >> I don't think your TTi TF930 has a GPS input to calibrate against, based >> on >> a quick perusal of the data sheet. I would guess that the calibration >> constants are thus fixed from the factory (including temperature >> coefficients). >> >> >> On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts >> wrote: >> >> I presume that this is what my TTi TF930 does. Calibration is closed box >>> so I guess the TCXO is free running and the micro inside just uses >>> calibration constants. >>> >>> James >>> >>> >>> >>> >>> >>> >>> >>> >>> -Original Message- >>> From: Paul Alfille >>> To: Discussion of precise time and frequency measurement < >>> time-nuts@febo.com> >>> Sent: Thu, 26 Feb 2015 19:02 >>> Subject: [time-nuts] Measuring frequency rather than tuning crystal >>> >>> >>> I have a couple of HP 5370s with the beaglebone brain transplant. They >>> come >>> with a nice 10811 that has a little adjustment screw. >>> >>> Testing against a >>> Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. >>> >>> I know the >>> traditional method would be to adjust the crystal slowly and >>> make careful >>> measurements, but since I have a fancy computer in there, I >>> wonder if I could >>> just adjust the frequency in software. 64-bit floating >>> point numbers should >>> have sufficient accuracy. All reported measurments >>> would be corrected for the >>> actual reference frequency. >>> >>> Basically, I'd have a 1000.226 Hz internal >>> reference. >>> >>> In fact, could I connect the beaglebone to a a GPS 1 pps source >>> and make >>> this a GPS-disciplined-software-corrected oscillator. >>> >>> So my >>> question is is this a known technique? The discipline feedback >>> circuit seems a >>> little different, I'd adjusting for drift and offset, but >>> not the gain of >>> control-oscillator >>> linkage. >>> ___ >>> 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. >> > > ___ 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] Measuring frequency rather than tuning crystal
All I was saying was most modern frequency counters, including my relatively cheap TTi TF930 have closed box calibration - you apply 10MHz as part of the calibration procedure and then it presumably stores constants internally. There is no tuning of the crystal. I think that much higher end counters such as the newer Keysight and Tektronix (rebadged Pendulum) do the same. It probably doesn't do any thermal calibration, purely frequency scaling at room temperature. So your proposal for your own set up should work fine. I wasn't suggesting that it calibrates itself from GPS - but in theory you probably could automate the process but if you had a GPSDO available all the time you might as well just use it as the reference input. James -Original Message- From: Paul Alfille To: jpbridge ; Discussion of precise time and frequency measurement Sent: Fri, 27 Feb 2015 20:09 Subject: Re: [time-nuts] Measuring frequency rather than tuning crystal I don't think your TTi TF930 has a GPS input to calibrate against, based on a quick perusal of the data sheet. I would guess that the calibration constants are thus fixed from the factory (including temperature coefficients). On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts wrote: I presume that this is what my TTi TF930 does. Calibration is closed box so I guess the TCXO is free running and the micro inside just uses calibration constants. James -Original Message- From: Paul Alfille < paul.alfi...@gmail.com> To: Discussion of precise time and frequency measurement < time-nuts@febo.com> Sent: Thu, 26 Feb 2015 19:02 Subject: [time-nuts] Measuring frequency rather than tuning crystal I have a couple of HP 5370s with the beaglebone brain transplant. They come with a nice 10811 that has a little adjustment screw. Testing against a Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. I know the traditional method would be to adjust the crystal slowly and make careful measurements, but since I have a fancy computer in there, I wonder if I could just adjust the frequency in software. 64-bit floating point numbers should have sufficient accuracy. All reported measurments would be corrected for the actual reference frequency. Basically, I'd have a 1000.226 Hz internal reference. In fact, could I connect the beaglebone to a a GPS 1 pps source and make this a GPS-disciplined-software-corrected oscillator. So my question is is this a known technique? The discipline feedback circuit seems a little different, I'd adjusting for drift and offset, but not the gain of control-oscillator linkage. ___ 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] Measuring frequency rather than tuning crystal
The TF930/960 does have a calibration procedure that is performed from the front panel. Basically, you feed it a stable input from any known source (so both 1 Hz and 10 MHz from a GPSDO should work) and then adjust until the displayed frequency agrees with the known input frequency. The resolution of this setting is quite a bit better than the stability of the TCXO in the box. Now, this process could occur either by actually adjusting the frequency of a VCTCXO in the box using a DAC, or by changing a calibration constant stored in the memory of the device. I suspect it's actually the former, because the instructions say that the adjustment path has a low-pass filter that you need to allow to settle. This wouldn't be necessary if the calibration simply changed a stored number. Dave On 27/02/2015 15:08, Paul Alfille wrote: I don't think your TTi TF930 has a GPS input to calibrate against, based on a quick perusal of the data sheet. I would guess that the calibration constants are thus fixed from the factory (including temperature coefficients). On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts wrote: I presume that this is what my TTi TF930 does. Calibration is closed box so I guess the TCXO is free running and the micro inside just uses calibration constants. James -Original Message- From: Paul Alfille To: Discussion of precise time and frequency measurement < time-nuts@febo.com> Sent: Thu, 26 Feb 2015 19:02 Subject: [time-nuts] Measuring frequency rather than tuning crystal I have a couple of HP 5370s with the beaglebone brain transplant. They come with a nice 10811 that has a little adjustment screw. Testing against a Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. I know the traditional method would be to adjust the crystal slowly and make careful measurements, but since I have a fancy computer in there, I wonder if I could just adjust the frequency in software. 64-bit floating point numbers should have sufficient accuracy. All reported measurments would be corrected for the actual reference frequency. Basically, I'd have a 1000.226 Hz internal reference. In fact, could I connect the beaglebone to a a GPS 1 pps source and make this a GPS-disciplined-software-corrected oscillator. So my question is is this a known technique? The discipline feedback circuit seems a little different, I'd adjusting for drift and offset, but not the gain of control-oscillator linkage. ___ 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. ___ 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] Measuring frequency rather than tuning crystal
I don't think your TTi TF930 has a GPS input to calibrate against, based on a quick perusal of the data sheet. I would guess that the calibration constants are thus fixed from the factory (including temperature coefficients). On Thu, Feb 26, 2015 at 3:36 PM, James via time-nuts wrote: > I presume that this is what my TTi TF930 does. Calibration is closed box > so I guess the TCXO is free running and the micro inside just uses > calibration constants. > > James > > > > > > > > > -Original Message- > From: Paul Alfille > To: Discussion of precise time and frequency measurement < > time-nuts@febo.com> > Sent: Thu, 26 Feb 2015 19:02 > Subject: [time-nuts] Measuring frequency rather than tuning crystal > > > I have a couple of HP 5370s with the beaglebone brain transplant. They > come > with a nice 10811 that has a little adjustment screw. > > Testing against a > Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. > > I know the > traditional method would be to adjust the crystal slowly and > make careful > measurements, but since I have a fancy computer in there, I > wonder if I could > just adjust the frequency in software. 64-bit floating > point numbers should > have sufficient accuracy. All reported measurments > would be corrected for the > actual reference frequency. > > Basically, I'd have a 1000.226 Hz internal > reference. > > In fact, could I connect the beaglebone to a a GPS 1 pps source > and make > this a GPS-disciplined-software-corrected oscillator. > > So my > question is is this a known technique? The discipline feedback > circuit seems a > little different, I'd adjusting for drift and offset, but > not the gain of > control-oscillator > linkage. > ___ > 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] Measuring frequency rather than tuning crystal
I presume that this is what my TTi TF930 does. Calibration is closed box so I guess the TCXO is free running and the micro inside just uses calibration constants. James -Original Message- From: Paul Alfille To: Discussion of precise time and frequency measurement Sent: Thu, 26 Feb 2015 19:02 Subject: [time-nuts] Measuring frequency rather than tuning crystal I have a couple of HP 5370s with the beaglebone brain transplant. They come with a nice 10811 that has a little adjustment screw. Testing against a Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. I know the traditional method would be to adjust the crystal slowly and make careful measurements, but since I have a fancy computer in there, I wonder if I could just adjust the frequency in software. 64-bit floating point numbers should have sufficient accuracy. All reported measurments would be corrected for the actual reference frequency. Basically, I'd have a 1000.226 Hz internal reference. In fact, could I connect the beaglebone to a a GPS 1 pps source and make this a GPS-disciplined-software-corrected oscillator. So my question is is this a known technique? The discipline feedback circuit seems a little different, I'd adjusting for drift and offset, but not the gain of control-oscillator linkage. ___ 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] Measuring frequency rather than tuning crystal
Paul, Right, there's no need to physically calibrate the LO when you can simply adjust all measurements in software, either inside the instrument or on the PC that's logging the measurements from the instrument. This technique is used for many high-end measurements and also extends to GPS post-processing for even greater accuracy. Look in the archives for GPS disciplined frequency counter. If you keep the raw data (DUT-REF, REF-GPS) you essentially avoid the entire rats nest of Vref, DAC, EFC, disciplining algorithms, and hard coded tuning constants. It just becomes a correlation in software. /tvb > On Feb 26, 2015, at 5:30 AM, Paul Alfille wrote: > > I have a couple of HP 5370s with the beaglebone brain transplant. They come > with a nice 10811 that has a little adjustment screw. > > Testing against a Thunderbolt or KS-24361 the 5370 is off by less than 1Hz. > > I know the traditional method would be to adjust the crystal slowly and > make careful measurements, but since I have a fancy computer in there, I > wonder if I could just adjust the frequency in software. 64-bit floating > point numbers should have sufficient accuracy. All reported measurments > would be corrected for the actual reference frequency. > > Basically, I'd have a 1000.226 Hz internal reference. > > In fact, could I connect the beaglebone to a a GPS 1 pps source and make > this a GPS-disciplined-software-corrected oscillator. > > So my question is is this a known technique? The discipline feedback > circuit seems a little different, I'd adjusting for drift and offset, but > not the gain of control-oscillator linkage. > ___ > 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.
