Hey y'all,

I just scored a Model 3 cart for my 7834 locally. After relocating the
scope and the modules I have from the floor, I played a little bit with my
7S12. Initially I had my S-52 in there with an S-4 sampler, just looking at
some SMA cables, got a rock solid trace.
I wanted to look at the SMA terminator I got with my NanoVNA, so I dropped
my S-6 sampler in there. With this sampler I see the signal just fine, only
it seems to be quite drifty or noisy.
I'm hoping this is a calibration issue of some sort, rather than a blown
sampling gate - or perhaps something downstream from the sampling gate.
Does anyone here have experience with this sort of thing?

Thanks,
Siggi

Hi Siggi,
A photo of your setup showing how the various parts are interconnected would help as would a picture of the waveform with all the S-6 noise and with the noise free S-4.

It is not clear to me what you mean when you say you dropped your S-6 in the 7S12. The S-6 is the correct sampling head for the 7S12 so why did you use the S-4 in the first place?
What were you seeing with the S-4 and why were you using it since it is not a pass-thru sampling head?
What is the vertical sensitivity where you are seeing the noise?
I would think a blown sampling diode would make the head totally useless.
It is possible the S-6 needs to be calibrated.
I have several S-4 and S-6 heads which I have never calibrated and until I ever get around to doing a calibration I have marked the ones that have the lowest noise to use first.

George Frye designed the S-4 and the S-6 heads and those were the fastest, and lowest noise, sampling heads available for many years after that. George was awarded patents for many very important inventions he created while at Tek. See https://www.freepatentsonline.com/3629731.pdf (a new type of sampling gate geometry), https://patents.google.com/patent/US3611003A/en (Random Sampling), https://patents.google.com/patent/US3434049 (TDR).
George Frye has 13 Tek patents. He left Tek and went into business for himself designing, selling, and servicing hearing aids in Portland. Since 1977 he has been awarded several patents for his inventions in this new field. I was also fortunate to meet George several times after he left Tek.

Agoston Agoston, Ph.D, joined Tek after the S-4 and S-6 were designed Agoston is another brilliant sampling expert. He also holds several sampling patents as well.
https://patents.google.com/patent/US7084716B2/en (Ultrafast sampler with coaxial transition)
https://patentimages.storage.googleapis.com/pdfs/US4812769.pdf (Programmable sampling time base circuit)
Agoston has 14 Tek patents - far too many to list here. Even Maria, his wife, has two Tek patents.

After he left Tek he formed HyperLabs in Beaverton in 1992 and began making his own drop-in sampling heads which had better noise specs and faster response times than the Tek heads. These are the Tek compatible HyperLabs sampling heads.
HL-11 100 pS 50 OHM BNC SAMPLING HEAD
HL-12 100 pS 10 KOHM BNC SAMPLING HEAD
HL-13 20 pS 50 OHM, K (SMA), SAMPLING HEAD
HL-14 <35 pS 50 OHM, K (SMA), TDR HEAD
HL-15 25 pS PHOTONICS HEAD
HL-16 25 pS, 50 OHM, K (SMA), PULSE GENERATOR HEAD

I have never found one of these for sale although I have been looking for over 15 years. When I was at his house in Beaverton two years ago I was too afraid to ask what one would cost new, or, far worse, I could not bring myself to ask if he might have a defective one I could have to add to my collection.
Agoston's company (https://www.hyperlabs.com/) has been producing ultra-broadband state of the art products since its inception 28 years ago.

Dennis Tillman W7pF

On Sat, Nov 14, 2020 at 7:36 PM Dennis Tillman W7pF <dennis@ridesoft.com>
wrote:

A photo of your setup showing how the various parts are interconnected
would help as would a picture of the waveform with all the S-6 noise and
with the noise free S-4.

I just had a piece of SMA-terminated coax from the S-52 to the S-4.
I'll get some pics of the traces in the morn'. The noise doesn't manifest
as a thick trace but rather as the trace bouncing up and down the screen
fairly randomly.

It is not clear to me what you mean when you say you dropped your S-6 in

the 7S12. The S-6 is the correct sampling head for the 7S12 so why did you
use the S-4 in the first place?
What were you seeing with the S-4 and why were you using it since it is
not a pass-thru sampling head?

I think it was in there simply because the last time I had the 7S12 in the
scope, the trace from the S-6 was wobbling about, and so I was trying to
figure out which part of everything was broken. All of this gear is
acquired from random places for no money to speak of, and it's all suspect
at this point in time :).

What is the vertical sensitivity where you are seeing the noise?

I'll have to look, but I'd think 50-100mV/DIV, given that the S-52 has a
200mV output amplitude.

I would think a blown sampling diode would make the head totally useless.

That's good to know.

It is possible the S-6 needs to be calibrated.
I have several S-4 and S-6 heads which I have never calibrated and until I
ever get around to doing a calibration I have marked the ones that have the
lowest noise to use first.

Yeah, I don't pretend to understand the circuits downstream from the
sampling gate, but I do remember thinking it all seemed very delicately
balanced. Hopefully I "just" need to adjust the head to get rid of the
wobble.

George Frye designed the S-4 and the S-6 heads and those were the fastest,
and lowest noise, sampling heads available for many years after that.

...
Yeah, I've read up on the sampling method used in the S-4 and S-6 heads.
Even knowing how they work, it still seems like they shouldn't :).

Siggi,

There are two preset pots in the S6 head for gate balance (R30) and 'gain' (R45), either could be noisy, but a more obvious suspect is the edge connector from the S6 to the 7S12 since the DC / low frequency feedback path has to travel through the edge connector.

Regards,

Roger

Hey Roger,

I tried cleaning the edge connector, but that didn't seem to help. So took
the head apart and gave the two pots as well as the board-to-board
connectors some D5 and I gave the pots each a wiggle. The "wobble" is now
gone and I have a rock-steady trace.
However, I clearly need to calibrate the head - not that it didn't already
need calibration. I guess I'll need to hunt for an extender (
http://w140.com/tekwiki/wiki/S-series_sampling_head_extenders) - people on
ePray sure are proud of their extenders...

In any case, thanks,
Siggi

On Mon, Nov 16, 2020 at 7:14 AM Roger Evans via groups.io <very_fuzzy_logic=
yahoo.com@groups.io> wrote:

Siggi,

There are two preset pots in the S6 head for gate balance (R30) and 'gain'
(R45), either could be noisy, but a more obvious suspect is the edge
connector from the S6 to the 7S12 since the DC / low frequency feedback
path has to travel through the edge connector.