really slow PLL

The ultimate way to do this would be to measure the phase of the xo at every rise of the 1 pps input, to nanosecond or picosecond resolution. That wouldn't be hard, but it would be overkill for the requirement to time-align power supplies.

If you only need a consensus, put the 40 mhz from the crystal onto the BNC though some resistor, they'll sort it out, like a table full of metronoms.

If you have control loops all over the place pulling in different directions maybe not so much.

mostlky no.

This proved hard to get: .

>

All very interesting. I've been digging, and came across a very interesting article, which happens to be open-access, which is all too uncommon.

"A geometric view of closure phases in interferometry", DOI:

.

I'm still digesting it, but basically deducing the underlying geometry allowed for some significant improvements.

Joe Gwinn

Am 25.07.22 um 18:31 schrieb Joe Gwinn:

I have not yet digested it, but can I assume that it won't help me to create a carrier that is phase noise wise better than averaged over 16 oscillators created equally bad?

More suitable for post-processing after-the-fact?

U. Rohde has the math for n injection locked oscillators in one of his books, but the formulas probably fall apart when you have to insert hard numbers for real oscillators you can buy, or build. Methinks he is more into multiple coupled resonators.

cheers, Gerhard

We made a lot of timing modules for a big laser facility. We get a

155.52 MHz fiber data stream and lock a local VCO to that, with jitter a couple of picoseconds. The phase detector, actually a time detector, is an ECL d-flop in a bangbang loop.

The lowpass has switchable bandwidth, acquisition mode and track mode, something like 8 KHz and 2 KHz.

As you suspect, no, it won't. Only better oscillators will help.

The big advantage of closure-phase methods is that one can recover the emission distribution of a very distant source by interferometry, while ignoring various practical imperfections of radio/optical telescope interferometers.

This works because the closure / kernel phase is an inherent property of the source that is not affected by those practical imperfections.

This is how we image distant quasars and the event horizon of billion-sun black holes at the center of some galaxies.

Yes. The classic is a room full of pendulum clocks slipping into synchrony. Discovered in 1666 by Christiaan Huygens, who invented of the pendulum clock in 1657.

The only math needed is differential equations, developed a few years later, in 1671. U. Rohde was a bit late to the party.

Joe Gwinn

Am 25.07.22 um 21:49 schrieb Joe Gwinn:

Or even more oscillators to average. :-)

Cheers, Gerhard

Yes, but the improvement is 5 dB per factor of ten oscillator count. Longer integration times may be easier.

Low-noise oscillator design is a career.

Joe Gwinn

I'm not sure--as I say, I haven't got a properly-thought-out scheme, but it seems as though it ought to be possible to combine the measurements to produce N-1 oscillator signals, each one N times quieter, so that averaging _those_ would get you to the N(N-1)/2 level.

It probably needs a whole lot of phase shifters or weighted summers (like a Wilkinson with attenuators), so it may well not be a win from a total-hardware POV. Seems like it would be worth a bit of thought, though.

Cheers

Phil Hobbs

As Kipling might say, "Not so, but far otherwise."

Cheers,

Phil Hobbs

Nah, even the simple averaging case you win SNR like N, so it's 10 dB per decade.

Cheers

Phil Hobbs

3 dB per doubling the # of oscs.

So, it will probably be 2 groups of 8 for my cross-correlating Timepod :-). As I wrote, the 5.0 MHz MTI-260 were relatively cheap.

Gerhard, DK4XP

Imagine a single circuit/pcb that has N crystal oscillator circuits, injection locked and summed, in an oven.

XOs near one another, namely in the same room, like to injection lock.

Sure. That only gets you 10*log(N), though, AFAICT. Looking at it from a phase noise POV, you win improved <delta phi> like sqrt(N), just as you gain lower <delta V> by parallelling JFETs.

Cheers

Phil Hobbs

Well, for phase noise test sets, the rule is that noise reduces as

10Log10[ Sqrt[N] ], or simply 5Log10[N], where N is the number of correlations performed, where what's being correlated is data-collection runs with a specified data-collection window durations. These windows can be over time or over devices, which should be equivalent in the noise floor.

So, getting to very low PN levels this way soon becomes impractical, and by far the best approach is to use a better oscillator. State of the art these days is a noise floor at around -170 dBc/Hz at 10 MHz. As always, 1/f^a noise can be a big problem, and it doesn't average out all that well.

We may be talking about different things.

Joe Gwinn

That's the physical layer; DMX is pretty holistic. I dunno - maybe there's a COTS DMX doohickey that can be pressed into service.

Some do; some don't. Session players from back when studio time was the dominant cost probably played the parts on a song you later heard on the radio on the first take.

There's too broad a spectrum to generalize. Some forms are better for people with mild forms of OCD.

Much does.

And there you go turning a perfectly good full duplex channel into a half duplex walkie-talkie channel :)

It'll be fast enough.

Interesting. With phase-locked sources, when you simply average the signals directly, the flatband amplitude and phase noise amplitudes go down like sqrt(N), i.e. the noise power goes as 1/N. It's just like additive noise.

Inside the loop BW, things are no doubt more complicated.

There are other situations such as OTDR where the amplitude dependence is sqrt(sqrt(N)), but that's on account of electrical power going as the square of optical power.

I expect so!

Cheers

Phil Hobbs

This might be the better oscillator.

It's a big lump of sapphire in a pool of liquid helium. Long term stability isn't wonderful, but short term stability is uniquely good.

" The team is re-engineering the device to work at 50 K by increasing the concentration of magnetic impurities in the crystal without introducing additional losses. That's a temperature that liquid nitrogen can't quite get to, but it's way easier than 6 K. "

Apparently the Australian Air Force has two of the 6K devices for their radar network. Probably beyond John Larkin's budget.