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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: CO2 Funny
Date: Tue, 28 May 2024 18:50:50 +1000
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On 28/05/2024 1:54 am, john larkin wrote:
> On Tue, 28 May 2024 01:05:18 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> 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)
> 
> You know nothing about this and are, as usual, all wrong. ALL the
> module timing is based on the 155.52 MHz clock, which is generated by
> a local PLL that is locked to the OC3 optical data stream.

All the module timing may depend on the 155.52MHz master clock, but the 
connection between edges on that clock and the signal the module puts 
out to fire the laser is decidedly indirect.

If you divided up the gaps between the 155.52MHz edges to generate your 
1psec accurate laser driving pulses you'd be able to claim a direct 
connection.

155.52MHz is a bit slow for a master clock in such a system.

>>>> 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.
> 
> Can you see the APC connector and the fiber?
> 
> https://highlandtechnology.com/Product/V880
> 
> The VCXO of the PLL is the shiny cube. It's mounted on tiny
> custom-made springs to isolate it from shocks from un-mating the SMB
> connectors.
> 
> Here's the PLL
> 
> https://www.dropbox.com/s/cobd3t4eorcsgrt/22S880D.pdf?raw=1
> 
> It uses a Dflop bang-bang ECL phase detector. I sure you don't
> approve.

The "circuit diagram" shows U11 as square block labelled ECL/VCO.

That makes it the top level block diagram - a more complete circuit 
diagram might be more informative, but you can't afford to reveal how 
cheap and nasty the guts of your board is.

> We originally uses a Vectron OC3 optical receiver module. It used a
> SAW filter to recover the clock and had very low time shift vs optical
> power. But they quit making it as OC3 fell out of fashion so I had to
> design a drop-in replacement. I'll use an SFP module if we do this
> again. 
> 
> Do I have to give the awards back?
> 
> https://www.dropbox.com/s/rb0fasr1flvvk51/NIF_Award.jpg?raw=1

Why should you? They are passed out to keep sub-contractors happy.

>>> 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".
> 
> Different project, a GHz squegg and not a sub-harmonic oscillation.

Squegging is a sub-harmonic oscillation. It repeats over periods longer 
than the primary oscillation frequency.

> The new oscillator fixes that and has superb jitter vs time open-loop,
> so the diversion was well worth it. It's so good that I might do a
> cheaper DDG based on the open-loop triggered oscillator.

It's presumably "insanely good" - by which you'd mean that we'd have to 
be nuts to take you seriously.

>> "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.
> 
> Wrong. It's sad that you are driven by vanity and hatred and not
> honest  interest in electronics.

The vanity here is all yours. If you were interested in electronics you 
wouldn't trying to pass off a block diagram as if it were an explanation 
of what you were doing.

--
Bill Sloman, Sydney