Tom Van Baak wrote: > Hi Ulrich, > > My understanding is that 1) the 53132A has a single-shot > resolution of about 150 ps, but also 2) it can do something like > 200,000 phase measurement per second for CW RF inputs. > > In frequency mode, the frequency computed and displayed > each second is the result of internal statistics on those > 200,000 samples, which in general is much better than two > single TI measurements made 1 second apart. > > In the best case of no correlation between input and timebase > the frequency resolution would be 150 ps / sqrt(200 000), which > is sub-ps. > > In reality, depending on the numerical character of the input RF > frequency, you don't get the full sqrt(200000) factor. Page 3-13 > of the 53132A user manual tries to explain this. But for most > input frequencies it is in the low picoseconds, which is why it > can be called a 12-digit per second counter. Google for > 53132a user manual for a copy of the manual. > > It is feasible to achieve a somewhat higher timestamp resolution (~20ps) and continuous sampling rate (> 1.5MSPS) than those of the 53132A relatively inexpensively provided that a DSP or similar processor is used to process the time stamp data in real time.
It is also possible to use a SR620 or a 5370 to take 1000 timestamps/sec. However may require using some external hardware (frequency divider). For maximum accuracy and precision the resultant data has to be logged and processed off line using a PC or other computer. > (As an aside, if you use a 53132A on a slowly warming OCXO > you can see the display resolution change when the magic n/m > threshold, mentioned in the back of the manual, is crossed). > > The bottom line is that the SR 620 or hp 5370 is a better counter > for TI (single-shot) measurements (e.g., comparing 1 PPS ticks). > But for CW frequency measurements, the 53132A is much quicker > due to this extreme internal oversampling. To be fair, I'm pretty > sure that other modern counters (e.g., Philips, Pendulum) also > use this frequency resolution trick. > > /tvb > Some Pendulum (A Philips spinoff) and Fluke (rebadged Pendulum) counters do use an improved (fit linear regression line to time sequence) statistical technique. Bruce _______________________________________________ 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.
