Re: Calibrating a PG506 w/o Sampling System


John Gord
 

Jim,
The HP 54120A/54121A combination also gives very good sampling performance, and is sometimes easier to find at a good price.
--John Gord

On Mon, Dec 7, 2020 at 10:40 AM, Jim Ford wrote:


Yeah, I believe that about the 7T11/7S11 pair, Chuck; I have a 7S12 and
a 7S11, with a couple of S-4 sampling heads and S-51 and S-53 for
triggering. PITA to get them to display anything on the 7904! At some
point, I will look for an 11800 series scope like the one I had at work
a few decades ago. I don't remember any issues with triggering back
then. And the SD-24 sampling head got top marks for pulse fidelity from
PicoSecond Pulse Labs (sold to Tek in 2014, IIRC) back then. Just got
to run the purchase by the finance committee (my wife)! She can't say
anything about the space it takes up; I have that covered with a 19-inch
rack next to my bench....

Jim Ford

------ Original Message ------
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: 12/7/2020 9:32:49 AM
Subject: Re: [TekScopes] Calibrating a PG506 w/o Sampling System

I do the PG506 calibration on a tek 11801C. It reveals
all.

But, using a 7104 will only make things worse, best not
done. As Raymond says, a PG506 adjusted to a pretty
waveform on a 7104 looks like something you could spear
fish with on a 11801C.

The 7T11/7S11 pair is supposed to be adequate with the
proper sampling head, but I have never been able to get
such a pair to work reliably. It kind of drifts into
a measurement, and drifts out. I never found the problem
to be worth investigating. If someone wanted to, I am
sure that my 7T11/7S11 pair could be had for a reasonable
price... whatever that is these days.

-Chuck Harris

Raymond Domp Frank wrote:
On Mon, Dec 7, 2020 at 05:17 PM, Jean-Paul wrote:


From transient CAL of 2467B, I can say its a tricky and iterative
process, and
the correct gens and fixtures are essential.

You may get by with a 1 GHz digital scope but not the Chinese, HP, TEK or
Lecroy.
First of all: Unless the edge settings have been changed, it's probably
not necessary to adjust them because your work hasn't influenced them. I
certainly wouldn't touch them without the right equipment.
OTOH, the transient response calibration of a PG506 is a very simple
adjustment, *if* you have the right equipment and perform the procedure
correctly: One capacitor for the positive edge (C1000) and one for the
negative edge (C940); optimize overshoot for both. That's it. Capacitor refs.
are for SM "Late Model": S/N B040000 up.
However, since you're adjusting a rise/fall time <= 1 ns (that's spec, in
practice usually 700 ps or better), your 'scope (as a rule of thumb) needs to
have a rise time of at most 20% of that: 200 ps. That means a BW for a 'scope
with Gaussian behavior of at least 1750 MHz, about 1400 MHz with many digital
'scopes.
So, using a 1 GHz BW digital 'scope won't crack it: The edge may look fine
on it but probably will have serious overshoot, which you won't see on your
(too slow) 'scope.
In practice, I'd consider 2.5 - 3 GHz to be the minimum BW required,
taking into account that actual rise/fall time of most units is about 700 ps.

Raymond








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