The datasheet quotes a measurement speed of > 5000 points per second. Under what conditions (frequency range, number of points per sweep, IFBW) were those measurements taken?
Using the example of the PicoVNA 106, we have:
- 140 kHz bandwidth
- 10 MHz to 6 GHz sweep
- 201 points (12-term cal): 37 ms for full s2p result set. = 184 µs per point for forward AND reverse sweep. >
5400 points/sec - 201 points (S21 cal): 25 ms for single S21 result set. = 124 µs per point for a forward sweep. > 8000
points/sec
Be careful when comparing with competitors, as they tend only to quote figures for the single-point single sweep. That compares with our faster figure above and not with the slightly longer time for a forward and reverse sweep necessary for a full set of S-parameters. This product is amongst the faster units available. See the competitive comparison on the website under the Reviews tab.
The sweep speed reduces according to bandwidth settings as the measurement at the output of bandwidth filter has to settle to its full accuracy.
If we first set a 10,001 pt sweep, the forward/reverse switch is proportionally less of an interruption and we can estimate its duration from the two trace lengths that we have.
At 140 kHz 170 us / pt for full s2p (two sweeps):
- Forward / reverse switch implied at around 14 µs.
Testing at other bandwidths for 10k point sweeps:
- At 10 kHz: 430 µs/pt for full s2p (two sweeps)
- At 1 kHz: 3 ms/pt
- At 100 Hz: 28.5 ms/pt
- At 10 Hz: 285 ms/pt