Sorry for taking a while to get back to you on this. It seems it is
time for me to add an S-6 manual to my binder of sampling stuff.
Here is why I do not believe the blow-by matters in this application:
When you are looking at the aberrations from a clean pulse measured by
a sampling head, instead of the impulse response which correlates with
the frequency and phase response of a linear network, you see charge
coupled through the sampling bridge from the fast edge and level
shift.
When measuring an AC signal, there are no fast edges and no DC level
shift to couple through the sampling bridge. In addition, the memory
gate is too slow to see any AC leakage. There is a simulation showing
the S-6 AC feedthrough here:
I like discussing this subject because it yields ideas for correcting
the annoying blow-by response in my S-4 sampling heads. Unfortunately
if it was easy to correct, I suspect Tektronix would have done so.
Do you actually need triggering to see just the peak to peak values? I
think you could add probe a different part of the generator circuit to
find a trigger so the leveled output could go only to the sampling
head.
On Mon, 18 Feb 2013 17:02:21 -0000, "Albert" <aodiversen@...>
wrote:
Hi David,
So far I didn't find effect of S-6 blow-by adjustment on sine wave amplitudes. I probably did something wrong, since the effect on square waves (tilt) is considerable. A change of C20 in the S-6 only causes a vertical shift of the sine wave. I tested some frequencies from 100 kHz to 1 GHz.
It's very annoying that the SG503 and my GR-type oscillators don't have a trigger output. Since the S-6 doesn't have a trigger output either I'm forced to use a CT-3 trigger pick-off and external triggering. With the S-2 I can compare internal triggering (CT-3 omitted) with such external triggering. The CT-3 has considerable effect on frequency response, about 6% to 8% downward trend when frequency is increased to 900 MHz.
Albert
--- In TekScopes@..., David <davidwhess@...> wrote:
The blow-by effect on frequency response could be tested. Grossly
misadjust it deliberately and see if the frequency response changes. I
found it to be the easiest thing to calibrate on my S-4 sampling heads
so I would not worry about temporarily misadjusting it.
I would also compare two different types of sampling heads like an S-2
and S-4 which have significantly different transient response
characteristics in the 10ns range do to design and see if they agree.
I may try the above with an S-1 and S-4 and my SG503 just to see what
kind of results I get.
David Hess