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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: CO2 Funny
Date: Tue, 28 May 2024 01:05:18 +1000
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On 27/05/2024 9:04 pm, john larkin wrote:
> On Mon, 27 May 2024 15:05:14 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 27/05/2024 4:22 am, Edward Rawde wrote:
>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:v2uhs7$39s6m$1@dont-email.me...
>>>> On 26/05/2024 4:38 am, Edward Rawde wrote:
>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:v2na16$1nvei$1@dont-email.me...
>>>>>> On 23/05/2024 3:52 am, john larkin wrote:
>>>>>>> On Wed, 22 May 2024 18:10:58 +0100, Pomegranate Bastard <pommyB@aol.com> wrote:
>>
>> <snip>
>>
>>>> It usually takes a while to work out why they did it that way, and it's pretty much essential to spend that time before you start
>>>> fiddling with the circuit. That wasn't true of the guy who'd put in the 741. He was very much in the John Larkin "if it sort of
>>>> works, ship it" camp.
>>>
>>> Which of John Larkin's products have you purchased and tested and what improvement
>>> do you think should have been made before it was shipped?
>>
>> Absolutely none of them. The timing gear he sells to the American
>> National Ignition Facility is based on a 1978 Hewlett Packard scheme,
>> written up in their journal, and it depends on starting up a 50MHz
>> free-running oscillator in a very predictable way.
> 
> Totally wrong, as usual. The NIF timing system is synchronous at
> 155.52 MHz across over 200 timing modules, about 2000 "clients"
> triggered every shot.
> 
> https://highlandtechnology.com/Product/V880
> 
> https://www.dropbox.com/scl/fi/74f60yne8cdlr53n1x1la/TUAP069.pdf?rlkey=4lp86ca0ztfuh055qyxtok9lm&dl=0

That write-up doesn't mention the 1978 Hewlett-Packard Journal article 
which you have talked about here.

It's a full bottle on the the 155.52 MHz timing scheme which is spread a 
across the whole site, which provides the start signal for your delay 
generators, but the individual delays generated don't depend on it at 
all (although it presumably provides the reference timing for any 
auto-calibration that you do)

>> Faster oscillators have less jitter, and while synchronising to a
>> continuously running faster oscillator twice may introduce extra jitter,
>> the net jitter on the time delay can be quite a bit less.
> 
> We deliver 1 ps timing resolution and a few ps RMS jitter to clients
> across a facility the size of a football stadium.

Perhaps, but you clearly don't understand what you are actually doing, 
otherwise you wouldn't be claiming that I was totally wrong, or invoking 
their optically distributed master clock as if were part of your system.

> We recently delivered our third system to NIF, the second generation
> beamline amplitude modulators. This helped them achieve over-unity
> fusion yield.

Not as much as a better designed system would have.

>> I had much the same problem in 1988 and went for a free-running 800MHz
>> oscillator.
>>
>> It turns out that the first version of John's 50MHz oscillator had a
>> nasty - if small - sub-harmonic oscillation and he's finally found a
>> better version.
> 
> It did not.

You recently told Phil Hobbs here that something like it did .. in the 
"fast discrete PHEMT one-shot thread".

"Tell me about that. My triggered 50 MHz colpitts oscillator squegged
at around 4 GHz. Tons of jitter.

I designed a new osc using a BUF602 and it's great."

Finding that prompted me to find his Murata 5GHz ferrite bead post, 
which I'd been kicking myself for not writing into my day-book.

I'm sure that you are going to tell us that this referred to a 
completely different, much more recent project, but I suspect that it 
was recycling the old idea and better test gear showed up an old problem.

-- 
Bil Sloman, Sydney