Rectify 500MHz Small Signal

From the late '70's onward I've probably used as many TL431's as OpAmps... the world's most "peppy" NPN ;-) ...Jim Thompson

Same here. I always wanted one in PNP flavor. IIRC there was (is?) a National part but it was expensive so I always sprung for another NPN behind the TL431.

On a sunny day (Tue, 29 Sep 2009 13:29:48 -0400) it happened Phil Hobbs wrote in :

I have never used PUTs, think I have some in the box though. I liked the UJTs so much because if you made a RC oscillator with those, then the frequency would be independent of the supply voltage. This because the intrinsic standoff ratio is fixed at say about 0.6. Later the 555 timer appeared, with f also independent of supply voltage... I kept using UJTs. They were easy to sync too.

one

diodes, as

dreadful IEEE

engineers

loved

them

and

essentially

switching.

detection,

low

of

good

DC

Not really. The 5000 and 7000 series scopes had sampling plugins - I have a bunch, and they're dirt cheap now - but they were pretty bad compared to the superb 11801-series stuff.

There are some little USB samplers, but they're very expensive.

Pumping scope is good for you.

John

They probably don't have the pill-packaged parts. Most of their stuff is surface mount. We use an SC-79 (practically invisible) 0.2 pF low-barrier schottky of theirs, SMS7621-079, 38 cents each.

Maybe you can drop a little antenna + diode pc board into the waveguide?

John

one

diodes, as

dreadful IEEE

engineers

loved

them

insane, and

essentially

switching.

detection,

low

of

good

DC

spectrum

There is an 11802 on Ebay right now for $1k but untested, "powers up". Thing is, I haven't gotten much more space here. A sampler for the 7704 over here would be nice. What is so bad with S-4 and 7S11? Ok, the

Probably not much of a market anymore and the TDR guys in the field dont' need a precision under a foot to figure where they have to drop the bucket of their Kubota.

"Room service, good evening. What would you like to order?"

...

"Send up some more room, please."

one

diodes, as

dreadful IEEE

engineers

loved

himself.

get them

insane, and

essentially

switching.

detection,

low

bias of

good

the DC

spectrum

be.

:-)

That stuff works, but it's not as quantitative as the later gear. And TDR is a fabulous thing to have, and the TDR on the 7-series stuff is really mediocre.

Isn't this beautiful?

ftp://jjlarkin.lmi.net/Z250A.jpg ftp://jjlarkin.lmi.net/Z250_TDR.jpg

(TDR of the test trace, J28 to J29)

Too much cheap surplus stuff on ebay, too. I'd love to do a cheapish USB TDR, but there's probably no good market.

John

I had a lot of fun with PUTs. They would drive TTL directly from that upper gate thingie.

John

Thanks John, That I would do in a design of mine, but I'm rather reluctant when I repair a commercial machine.

Rene

What amount do you consider expensive?

-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... "If it doesn't fit, use a bigger hammer!"

--------------------------------------------------------------

$12K is expensive.

John

on one

diodes, as

dreadful IEEE

engineers

loved

himself.

get them

insane, and

essentially

switching.

detection,

The low

bias of

ohm,

good

stored

the DC

spectrum

be.

:-)

That is indeed beautiful. Although, to be honest, I never really had an urgent need for TDR. Occasionally I resonate stuff out with a dip meter. But even there it has happened that I didn't use for a while and the battery oozed out. I also have this as a backup:

Knock on wood that the tubes don't go out on me. Of course, when things resonate above 400MHz I am up the creek unless I kludge something.

There probably isn't much of a TDR market. But I believe there would be a market for a sampling scope app where people can check (repetitive) timings to within several picoseconds. With comm data rates almost in the two-digit GHz-range that market should be growing.

Of course it would need to beat the surplus stuff in price or at least be on par. The added benefit is the easy documentation via mouse click.

Yes. I the US one can buy a fairly decent passenger car for that kind of money.

Trace impedances matter a lot to us. Board houses sometimes take liberties with multilayer stackups and copper thickness, so we try to build in test traces for both impedance and resistance when it matters. That test trace in the pics takes a tour of all 4 board layers, so we can see all the impedances. It's even more fun on

It's also cool to add SMAs to access power pour layers and TDR them. That blows away all sorts of cockeyed theories about bypassing high-speed stuff.

Transitions, like pcb-to-connector, are also interesting to TDR. Leads to x-acto slashing sometimes.

One market for a small, affordable USB TDR would be to sell to board houses. The Polar Instruments stuff (from the Channel Islands, another story) is expensive and very dated.

John

Ok, I understand that. But since you know the geometries from the Gerbers can't you just measure total resistance and capacitance to see if things are within ballpark?

Those theories sure are weird :-)

That is next to impossible to do without TDR.

But it sure is beautiful there:

I could imagine living there, we are not the kind of folkss who'd get cabin fever because of the confines of a smallish island. As long as there are some nice pubs.

Expensive indeed. Any idea what makes these buggers so expensive?

The usual. High NRE costs, low sales volume, combined with the desire to make a living.

You wouldn't believe what I've seen in some electro-optical gear. A couple of

We, at least, use metal:

John

And I bet you have a TVS across the 12VDC line. I'd rather that folks would buy from companies like yours. But often they gravitate towards those that they know from the past or that have a "name" in their field. The gear is sometimes fancy but very pathetic. A sad episode was a TEC plus laser diode driver combo box, very expensive. Janitor plugged in his big industrial Hoover, turned it on, all the LEDs on the box lit up and then ... *PHUT*

It's similar in other fields. I've lost count how many times fairly simple test jobs were done with very expensive NI gear and LabView while we did it for around a hundred bucks with a LabJack at a client. It is often impossible to convince folks that this much less expensive route can yield the same results.