Third order IMD in photomultipliers--weird behaviour

I had the signal advantage of learning Fourier theory from Ron Bracewell himself. One of the best teachers I ever came across. He really taught us how to think in k-space with little effort, by way of hammering on about six theorems and ten rules of thumb. His book is an excellent read for when you're between bouts of snow shovelling. ;)

Yup. When I don't understand something I care about, it's like having a pebble in my shoe. Eventually I have to fix it.

Yup again. No colleagues round here, except for Beautiful Layout Hunchback, who has been taking physics and math but isn't there yet.

Nope. The other main reason I hang around SED is that I learn stuff. For instance, you supplied the key missing piece, namely the quadratic possibility, and I'm having fun with JL's balun gate driver.

Yeah. Years ago, I spent one vacation going through Papoulis's statistical signal processing book, but it didn't really stick too well. Maybe I didn't do enough of the problems or something.

Should be before New Year's.

Cheers

Phil Hobbs

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o can't think straight. The former is childish, the latter is more or less an obligation when you have to explain how they could possibly adopt certai n nonsensical views - James Arthur's persistent identification of modern so cialism with communism is a case in point. When a man as clever as he is ma kes - and persists in - that kind of mistake, he's got to have been brainwa shed.

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my rhetoric. If you've managed to miss that you haven't been paying attent ion (not that anybody in their right mind should - I'm trying to jump up an d down on the presentation of nonsense, and that's about as interesting as taking out the trash).

t realised that he'd been called in to solve the problem after the customer had found it, in hardware that the customer had put together, and I did go on to say that most of the problems that one runs into with photomultiplie rs aren't easily predictable, or easily anticipated.

he customer ended up with that much anode current escapes me - noise proble ms mostly show up closer to the photocathode, and keeping the gain high ove r the first few dynodes minimises them.

r the amplifier they use in the anode-current to voltage stage.

of the time. At Cambridge Instruments we used photomultipliers in the secon dary electron detectors, and the dynode chains were never pretty. The one I designed had the resistors and zener diodes in the chain perched up on Tef lon (PTFE) insulated pins that plugged into holes drilled into a printed ci rcuit board.

oduction line a lot happier - and they did bitch about it to me (amongst ot hers) from time to time. If you had any sense you paid attention to that ki nd of bitching.

thren.

akes much too long, and would bore the brighter readers to tears.

ook stuff out of Julia Child's "Mastering the Art of French Cooking", but I 've never found that discussing it adds much value.

Wow, Bill I'm sorry your whole post just reads (to me) as one continuous insult to some and then all of us. My playground comment was mostly about myself... I found myself at the "playground" level of saying I like Susan more than Mary... Which doesn't matter all that much as far as SED is concerned. Having both Mary and Susan here is more important, as they both will have different things to add.

(OK there was a bit about pmt drives, and not liking to talk about food. Science, sex and food (in no particular order).. and the next best thing to having science, sex or food, is talking about it!)

George H.

Hey the plows on the truck and the snow tires are going on the car tomorrow. I'm ready.. mostly. (It's a pretty wimpy winter so far.) Re Bracewell the third edition is a little spendy, but the

Yeah certainly to learn new stuff! I don't "get" JL's balun gate drive. Is he doing some RCL thing to deal with the gate C? Amps in nanoseconds is awesome, I'm mostly happy with an amp in a microsecond or so.

Re: IMD and shot noise, Were the IMD spurs buried in the shot noise such that you couldn't see them without signal averaging? (The size of the shot noise depends on the pmt gain..) If so that would help with my understanding.

George H.

In the 10-Hz resolution bandwidth I was using, they stuck up a fair bit abo ve the noise except at the lowest levels (

bove the noise except at the lowest levels (

Huh, OK 10 Hz out of 20 MHz... I'm not sure exactly how to think to think about that... which is somewhat embarrassing. We sell a "physics package" to go along with the SRS 770 spectrum analyzer. One of the electronic things I made was a "hidden" single frequency source underneath noise. With clicks of a dial the sine wave becomes smaller and at a different frequency. It quickly becomes very hard to find.. isn't that also like averaging? (I sent my daughter a link to Bracewell for Xmas.)

George H.

I post a statement of fact - Phil Hobbs' customer would have been happier if he'd consulted Phil Hobbs and got a better dynode chain to start with - and both you and Phil Hobbs see it as an insult.

I'm a bit more worried that George Herold goes along with the misconception.

John Larkin experiences what he finds to be inadequate praise as an insult, and finds my unwillingness to praise him as extravagantly as he feels he deserves to be a deliberate insult, but it is hard to take his bleating seriously.

Phil Hobbs was presumably insulted that I could imagine that he would have given the customer a duff dynode chain in the first place - but - as he said, you'd have expected Hamamatsu to have got it right by now, so it's a pretty thin-skinned reaction.

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who can't think straight. The former is childish, the latter is more or les s an obligation when you have to explain how they could possibly adopt cert ain nonsensical views - James Arthur's persistent identification of modern socialism with communism is a case in point. When a man as clever as he is makes - and persists in - that kind of mistake, he's got to have been brain washed.

or my rhetoric. If you've managed to miss that you haven't been paying atte ntion (not that anybody in their right mind should - I'm trying to jump up and down on the presentation of nonsense, and that's about as interesting a s taking out the trash).

n't realised that he'd been called in to solve the problem after the custom er had found it, in hardware that the customer had put together, and I did go on to say that most of the problems that one runs into with photomultipl iers aren't easily predictable, or easily anticipated.

the customer ended up with that much anode current escapes me - noise prob lems mostly show up closer to the photocathode, and keeping the gain high o ver the first few dynodes minimises them.

for the amplifier they use in the anode-current to voltage stage.

t of the time. At Cambridge Instruments we used photomultipliers in the sec ondary electron detectors, and the dynode chains were never pretty. The one I designed had the resistors and zener diodes in the chain perched up on T eflon (PTFE) insulated pins that plugged into holes drilled into a printed circuit board.

production line a lot happier - and they did bitch about it to me (amongst others) from time to time. If you had any sense you paid attention to that kind of bitching.

cook stuff out of Julia Child's "Mastering the Art of French Cooking", but I've never found that discussing it adds much value.

You are beginning to sound like John Larkin. I get the impression that your idea of playing nice would be to say nice things about everybody who posts here, and discriminate by saying nicer things about the people who have so mething useful to say.

As an Australian, I was brought up to call a spade a bloody shovel, and whi le this didn't go down all that well in the UK, my time in the Netherlands restored my faith in speaking briefly and to the point.

Some contributors are more valuable than others, and some strike me as comp lete wastes of bandwidth.

Even fewer who can (and are willing to) think clearly about the complicated ones.

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s who can't think straight. The former is childish, the latter is more or l ess an obligation when you have to explain how they could possibly adopt ce rtain nonsensical views - James Arthur's persistent identification of moder n socialism with communism is a case in point. When a man as clever as he i s makes - and persists in - that kind of mistake, he's got to have been bra inwashed.

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for my rhetoric. If you've managed to miss that you haven't been paying at tention (not that anybody in their right mind should - I'm trying to jump u p and down on the presentation of nonsense, and that's about as interesting as taking out the trash).

adn't realised that he'd been called in to solve the problem after the cust omer had found it, in hardware that the customer had put together, and I di d go on to say that most of the problems that one runs into with photomulti pliers aren't easily predictable, or easily anticipated.

hy the customer ended up with that much anode current escapes me - noise pr oblems mostly show up closer to the photocathode, and keeping the gain high over the first few dynodes minimises them.

h for the amplifier they use in the anode-current to voltage stage.

lot of the time. At Cambridge Instruments we used photomultipliers in the s econdary electron detectors, and the dynode chains were never pretty. The o ne I designed had the resistors and zener diodes in the chain perched up on Teflon (PTFE) insulated pins that plugged into holes drilled into a printe d circuit board.

e production line a lot happier - and they did bitch about it to me (amongs t others) from time to time. If you had any sense you paid attention to tha t kind of bitching.

it

ly cook stuff out of Julia Child's "Mastering the Art of French Cooking", b ut I've never found that discussing it adds much value.

ur idea of playing nice would be to say nice things about everybody who pos ts here, and discriminate by saying nicer things about the people who have something useful to say.

No, sometimes hard things have to be said. (But rarely here on SED.) I gu ess I behave as I was raised. There was a Herold tradition that I was taught y oung and often... (mostly by Granma and Aunts.) that if you can't say something nice , it is often best to say nothing at all. (I often find my self deleting my crankier posts... writing them makes me feel a bit better, but then ther e is nothing to be gained by sending them. And I hit the discard button.)

George H.

hile this didn't go down all that well in the UK, my time in the Netherland s restored my faith in speaking briefly and to the point.

mplete wastes of bandwidth.

The spurs aren't too large compared with the noise if the dynamic range of the image is small. However they cause ghosts in the image, which as anyone who used to watch analogue TV can tell you, is objectionable.

I like Bracewell's 2nd Ed. better than the 3rd anyway.

Cheers

Phil Hobbs