Yes, my theory on this is that we're talking about such minute changes in frequency, that even a tiny outside temperature change can have an effect. I wish I had some other unit to compare against - not sure if this is normal. Do you think the stray sunbeam was impacting the outside temperature of the oven, or is there perhaps some chip-scale IC inside these units?
You mean like the RPi a few months back? I think these units are too old for that. If I remember correctly, it took the unit several minutes to recover after I blocked the sunbeam so I think it was a thermal effect.
I have a Z3801A which is equipped with an HP double-oven oscillator. The oscillator is surprisingly crude for an HP unit. They basically took an HP 10811 oscillator (really good reputation, by the way), made a few internal changes to increase the electrical tuning range, and then wrapped another heater and insulation around it. There are autopsy photos online. Once you dig out the oscillator, it even has the original label on it. In spite of how crude it is, it works quite well. The entire unit is in a solid steel box with a reasonable number of slots for cooling. Thermal changes don't really bother it - even at these tiny levels.
I wonder why these Lucent units are so recommended on Time-Nuts. There seem to be a lot of compromises to them: 15 Mhz sine instead of 10, "dirty" 10 MHz output only available on redundant unit, low sensitivity 8-channel GPS, funky connectors (power and others), ... And so far the performance does not seem to match the alternatives out there. Am I missing something here?
BTW - my HUD has now risen to 6.5us. It was as low as 1.9us at one point. Not sure what's causing this? Maybe this is a normal pattern as the crystal breaks in?
Rather than venture onto the roof, one (lazy) option would be to just dig it out once every 6 months (or once a year) to calibrate your counter if it now has the high stability OCXO option fitted.
If you fit an external antenna on the rooftop will you be leaving the GPSDO running 24/7? I don't leave my OCXOs running 24/7 and the generators just get used as and when required and they still seem to perform well. Although they are all >10 years old and the 2024 Marconi must be >18 years old.
@ GOHZU , do you happen to know the model of your epson oscillator?
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.
Have you seen a write-up on either of these units? The Trimble board actually says "Designed in the US" on the board. I am curious where it comes from, and how it performs relative to the other unit you mention, which I think is just the BG7TBL design with a different OCXO.
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.
Have you seen a write-up on either of these units? The Trimble board actually says "Designed in the US" on the board. I am curious where it comes from, and how it performs relative to the other unit you mention, which I think is just the BG7TBL design with a different OCXO.
the oscilloquartz board is a surplus gpsdo that comes out of some huawei telco equipment. it uses the exact same bg7tbl adapter board as the trimble. it's not just an ocxo swap.
You know, I just don't believe these TI numbers. Perhaps I don't understand what they represent. I hooked up the Lucent GPSDO 10MHz output to my 53131A, which has its own OCXO that has been calibrated to the Lucent.
Now if the Lucent was really drifting by 10 - 50ns per 1 second interval, unless the timer OCXO was drifting in sync (impossible), I would expect to see variation in the 0.1Hz digit. Instead, it is rock solid all the way out to the 0.0001 digit.
I guess maybe I need to sign up for the time-nuts mailing list and ask someone to explain it (or maybe Ed can explain here).
What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.
You know, I just don't believe these TI numbers. Perhaps I don't understand what they represent. I hooked up the Lucent GPSDO 10MHz output to my 53131A, which has its own OCXO that has been calibrated to the Lucent.
Now if the Lucent was really drifting by 10 - 50ns per 1 second interval, unless the timer OCXO was drifting in sync (impossible), I would expect to see variation in the 0.1Hz digit. Instead, it is rock solid all the way out to the 0.0001 digit.
I guess maybe I need to sign up for the time-nuts mailing list and ask someone to explain it (or maybe Ed can explain here).
Believe your counter. The GPSDO is reporting the TI between its PPS and the calculated PPS based on the received signals. Problem is, the received signal gets distorted by the ionosphere and maybe by multipath. This creates jitter in the calculated result. Over a long period, this jitter averages out to zero. The OCXO's function is to act as a flywheel to filter out the short-term jitter. The PPS is then generated from the OCXO. The 'gotcha' here is that in the RFTG, the averaging appears to degrade the OCXO's performance - or doesn't completely filter out the short-term jitter.
There are a few things that can be checked to ensure that the jitter is minimized. Like they say, "Location, location, location". If the GPSDO doesn't have its location figured correctly, this can be a major cause of jitter. I don't remember if the RFTG has this feature, but some GPSDOs give you the option to set the length of time for the location survey. Longer is better! The survey is just as vulnerable to jitter as the PPS. A longer survey helps average out the jitter. Give it a day or two - compare the before and after results.
Note that measuring the output with a frequency counter isn't a very precise measurement because the counter's gate time results in an averaging function that hides things. It's much more effective to measure the time interval between the GPSDO and another local reference. Of course, you have to have another reference! You also need to be able to capture the readings and log them to a PC.
Ed
What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.
What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.
I did a tear down and test of the BG7TBL unit here..
https://drive.google.com/a/skybase.net/file/d/0B9Oysj7clpT7YTBWSjlfNTI1aTQ/view
While I don't have the resolution of KE5FX's test rig ( he has a Cesium standard!) my Thunderbolt based test setup did not show that error.
regards
Tim
Very nice. From which eBay seller did you purchase this unit?
Very nice. From which eBay seller did you purchase this unit?
Thanks - I bought from fly-xy, he has a bunch of interesting RF stuff. URL for the GPSDO I bought here...
http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/121530825744
And here is a newer model with Huawei internals ...
http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224
and yet another model with Trimble internals...
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power/131564496688
regards
Tim
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/