"Sampler??"

According to the block diagram, the output of the sampler-cum-harmonic mixer should be between 20Mhz and 30Mhz. However, when I insert a tee into that part of the loop, all I'm seeing is a bunch of random garbage signals in the range of 650kHz to about 9Mhz (fortunately I've a spare spectrum analyser to see this with). That unexpected result indicates there's most likely something wrong with the "sampler" *or* one or both of the signals going into it. However, before I can start to investigate that part of the loop, I needed to know what the sampler *should* be doing. Now I know it's just HP's fancy term for a harmonic mixer I have a much better understanding of the circuit. My thanks to all who contributed here.

I think in this context, HP is using the term "sampler" to mean something which 'sniffs' a small amount of a signal for testing purposes. Like a few turns of wire around a transmission line will 'sniff' a small sample of what's going on in the line. Where I went wrong was rigidly thinking HP meant 'sampling' in the manner a sampling oscilloscope works. That's what threw me. I tend to interpret things very literally. :(

Wrong. The kind of sampling going on produces an output at a different frequency than that of the signal being tested/monitored/sampled.

That implies some kind of non-linear interaction with a "sampling" input at yet another frequency.

It's the HP8566B - a very well known lab-grade analyser of the day which many RF designers still use. There is a *ton* of service info on this model online. However, I have not been able to see a *proper* schematic for the "sampler" in the A11A5 board which is where the issue is.

HP always put the theory notes in the HP Journal, so I'd suggest searching there for the HP8566B, in the issues around when the instrument was first introduced.

Joe Gwinn

Yes, I have all of those and more. I think altogether there are 7 very large manuals for this analyser. However, I've not been able to find a single actual schematic which gives component level detail of what they call the "sampler" - and that's unusual, as they've given a great deal of attention to providing very full service details in all other respects.

I wouldn't trust myself to build something like that. I'd get spurious signals and wouldn't know if they're truly spurious or not. Plus I like boat anchors and their imposing presence. I also like lots of knobs, because lots of knobs = no menu system and no menu means it's a lot easier to find what you want.

I have bespoke audio generators. Boat anchors again.

I have an HP audio spectrum analyser - another monster - which I could power up if necessary for that purpose. It would probably go bang, though. Hasn't been switched on for years, you see.

This analyser is well over 30 years old, so whatever's gone wrong is most likely age-related and wouldn't have come to light for many years. Fortunately there's a lot of info out there - *if* you can find it!

The sampler in the SA schematic is precisely the sort of sampler used in a sampling scope. It contains a step-recovery diode impulse generator and no doubt some sampling diodes.

On the lack of a schematic, I did dig into how it worked many years ago, and as I recall it was based of some fancy abuse of a slotted rectangular waveguide which supported various orthogonal modes - this cannot be described by any lumped-parameter circuit.

Try this:

US4647795A, Travelling wave sampler, Agoston Agoston, Beaverton, Oreg. Tektronix, Inc., Beaverton, Oreg. granted 3 March 1987.

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It does have schematics, in a manner of speaking.

Joe Gwinn

The schematic of A11U1 might only show three diodes, the srd and two schottkys - the magic is in the physical construction. Flip chips, ceramic substrate, artfully designed micro strips and what not. I doubt that assembly is amenable to repair.

The HP8566 seems to be notorious for fiendish YTO unlock problems which more often than not end up being trivial preset pot wiper lifts or aged capacitors in the YIG coil drivers.

August 1979 - available many places including Hpmemoryproject and hparchive

I hope it's not that, then!

True. There are all sorts of potential failure points. HP do provide about

How can you say that when you haven't seen the schematic? If you've been able to find it online somewhere then kindly post a link to it here.

Quite.

You posted an excerpt from the HP manual where the sampler is described.

I have an old HP sampling plugin that uses a machined block slotline structure. 3 GHz bandwidth as I recall.

But you said: "The sampler in the SA schematic is precisely the sort of sampler used in a sampling scope."

So you must have had sight of the schematic. I'd really appreciate it if you could post a link to it.

If it's Agoston's, it's a genuine time-domain short-pulse sampler, not an attenuator pick-off.

Jeroen Belleman

Doesn’t this predate Agoston’s work?