I do not have any in dependant confirmation but I suspect given the
relatively low frequencies involved for the sampling heads up to 5%
loss that they will be very close to ideal. I do not know of a better
way to calibrate for a constant level that does not require something
else already calibrated to a better standard except for a thermal RMS
based design which itself can be calibrated at DC.
If you have even an unleveled microwave signal source, you could use
it to find the first null in the sampler frequency response which
would tell exactly what the sample gate time is.
Do you mean overshoot or blow-by? I know my S-4 sampling heads have a
lot of blow-by aberration or whatever that is at about 10ns but show
ideal pulse response as far as I can test. My working S-1 shows no
blow-by with the same input pulse but my best flat level pulse
generator while clean is not fast enough for the S-4.
On Fri, 15 Feb 2013 22:35:37 -0000, "Albert" <aodiversen@...>
wrote:
Hi David,
In my response to Ed I said something about VSWR; that crossed your message.
Your calculations (indeed needing the famous sin(x)/x) assume a perfect rectangular windowing function. Do you have any reference for how good or bad this approach might be in practice? The overshoot in step response of my S-4 is in conflict with this theoretical approach.
Albert
--- In TekScopes@..., David <davidwhess@...> wrote:
I think using a sampling oscilloscope for flatness calibration is a
great idea. The sampling heads are both very high bandwidth and have
a very predictable frequency response. The weakest links will be the
SWR match and termination but that applies to any system. You can do
away with cable losses by using a sampling head extender.
If you take the 3db bandwidth numbers I posted earlier and divide by
4, that is the point where the sample head output will be down by 2%.
The second number shown is where they will be down by 1%:
S-1 260 MHz 190 MHz
S-2 1.18 GHz 869 MHz
S-4 3.60 GHz 2.61 GHz
S-6 2.99 GHz 2.17 GHz
I think this is the first time I have had a need to do math involving
a sin(x)/x function.
David Hess