On 4 October 2014 13:24, Tom Van Baak <[email protected]> wrote: > Dave,
Hi Tom > Thanks for the raw data. Attached is my plot. Your data looks ok to me. Great > If you're interested here are some random comments about your > 8720D-1D5-oscillator-frequency.csv file: Sure > - Thanks for including the description of the data as comments in the file. I > can't tell you how many times I get data files from people and you have to > play "20 questions" before you know what the columns are, or what the units > are, or what the sampling interval is, etc. Yes, I can imagine it. Some people have some odd ways of presenting data. Slightly different, but I recall trying to help a student debug her software. It became apparent that all variable names were Disney characters! The number of photons might have Aladdin, the absorption coefficient MickyMouse, the scattering coefficient SnowWhite ... I believe she went onto work with missiles, which is worrying. > - Thanks for including the elapsed time (column 6) as part of the data set. > This is the preferred way to determine the sampling interval; 6.3 seconds in > this case. It seems the obvious one to me. > - You have 355 data points. Notice that the last 319 measurements are all > 9.99999400. This is partly due to the fact that the OCXO has warmed up by > this point. But this is mostly due to the fact that your OCXO is now more > stable than the counter has resolution. Yes, I see that. > - Out of habit my plot uses ppm units rather than Hz. I converted your > frequency measurements to relative frequency error. For example, a frequency > of 10.00013100 MHz the error is (10.00013100 - 10) / 10 or 1.31e-5. The five > frequency lines above simply become: > 2.5e-6 > 1.3e-6 > 0.0 > -1.2e-6 > -1.9e-6 Yes, I can see the logic of that. At least to a time-nut. Not so sure I would present it like that to most people. > and this shows that even though it's a 7 digit counter there are only 2 or 3 > digits of resolution (the DUT being quite close to 10 MHz). I should have a look to see if that can be improved. I hacked the the software to collect that together in 15 minutes or so, but it was heavily based on something I wrote in 2008. At that time, the job was urgent and on some occasoins I was working to 2 AM to get the code finished. I doubt it well written as it could be. Perhaps the resolution could be improved. I guess I should also get a better counter. I used to have a HP 5370B, but sold it to someone on this list - a decision I later regretted. I have thought of buying another microwave counter (mine is pretty dead), but I doubt that would have the resolution of a lower frequency model. And microwave counters tend to be quite expensive. > - By the time you get to all the 9.99999400 MHz readings, the counter is down > to 1 digit of resolution, e.g., -6e-7. Yes. > - Most people plot points and draw interpolated lines between them. The > Stable32 plot I attached shows a staircase. This is partly due to the fact > that the raw data is quantized in both the x and y axis (sample quantization > is 6.3 s, frequency quantization is 1 Hz). It is partly done to convey that > frequency is inherently an average across some interval rather than a point > measurement. I see Stable32 is some specialist software for time-nut related items. > Again, none of this has any impact on your original question about your VNA > timebase, but I thought you might be interested in what's hidden in the data. > Now imagine the fun you could have making 12 digit measurements... I guess I will have to look for another 5370B! If I recall correctly, when I did look some time ago at getting another TI counter, the Agilent 53230A seemed to have some specifications *worst* than the 5370B it replaced. It was not clear it was an upgrade. This 53230A on eBay does not seem very good value, at about 60% *more* than the price of a new one from Keysight!!! http://www.ebay.co.uk/itm/COUNTER-TIMER-350MHZ-12-Digits-20PS-53230A-/ Perhaps I should ask what discount I could get if I buy 10! I just stuck an offer on a SRS 620, which is sold as seen. I'll take a chance it works if my offer is accepted. Dave _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
