really slow PLL

DMX for this is like hunting deer with an artillery piece. DMX is for the big-ass risk scenarios in distributed topologies; this is a lot less profound.

? it's a 250kbit uart on RS485, hardly rocket surgery

Engineering is composition. Composition is the thin edge of the musical wedge. Musicianship is different; it's pattern identification. As is composition but in a different way. But it is all the same thing.

It all depends on which wall you prefer to have your back against.

Over where they MATLAB.

Right, it's glorified MIDI.

The lazy guy within me always tries to use an N connector to BNC adapter on my boat anchor spectrum analyzer. He convinces himself he's only interested in frequencies less than 2 GHz, so, what's the harm?

High performance WiFi antennas also use N connectors to squeeze out every last iota of performance. You need a DIY N connector to reverse- polarity SMA to connect such antennas to consumer WiFi devices. Danke,

Biggest 'gotcha' is the lack of good shielded TP connectors. I had only UHF-style twisted pair shielded connectors last time I wanted some, and that's a polarity-insensitive connector. We applied paint markings to get it straight.

MiniDIN 3 (don't trust the shield connector) was what Apple used for their LocalTalk/Appletalk hardware, and of course there are microphone connectors (big 'uns)) but for cheap 'uns, RJ--11 (6P4C and use the second pair) wasn't good (I needed to pass significant current) and Lemo offerings were... neither inexpensive nor locally stocked.

I've implemented it on several chipsets including Motorola 68488, Intel

8292 and TI 9914. We even implemented full pass control between peer controllers and our own bus analyser to capture bus transactions (which after a redesign could not be blinded by HP's IFC tricks).

Later we reworked things for IEEE488.2 in the early 1990's but I dropped out of that game not long afterwards to go and work in Japan. Ethernet had made significant inroads into the instrument market by then.

And the accepted line makes sure the slowest thing on the bus gets the message which is why it tended to slow down as longer cables and more kit was added. It tolerated much longer cables than the official standard permitted with only modest loss of speed.

It surprises me that it is still present on *any* modern instruments. I expected it to survive on useful legacy kit until about now though.

Plenty of labs will have good working kit that still uses that interface and it is plenty fast enough for a lot of ordinary lab use.

I've always wondered about musicians. They have to play a piece hundreds of times to get it right. Some have surely performed something thousands of times. Don't they get bored? Apparently not.

I design something, finish, and then want to design something entirely different.

It depends on boredom thresholds.

SCPI is send-and-forget. There is some query you can send to ask if the last command worked. And you can have an error queue that you can interrogate now and then for historical forensics.

I told the customer that damn the specs, every command is going to reply with data, an error message, or "OK". They agree.

Plus you can get GPIB-Ethernet adapters for fairly cheap. We use one made by the estimable Abdul at Prologix, which works pretty well--we've used as many as three instruments with it at a time--two scopes and a spectrum analyzer. Did it just yesterday, in fact.

Cheers

Phil Hobbs

N connectors are almost identical to BNCs internally--in fact you can mate an N male to a BNC female very nicely.

I use SMA for everything above about 2 GHz anyway. (Some of my test gear uses expensive K (2.8 mm) or very expensive V (2.4 mm) connectors, but those all have SMA adapters on the front.)

Cheers

Phil Hobbs

Yes. This is exactly how part of NTP works, in particular the FLL (Frequency Lock Loop). Battle-tested. That's where I got the idea. NTP was developed in the early 1980s, shortly after Ethernet made such a thing useful.

This kind of thing is extensively discussed on Time Nuts.

Yep.

I forgot to mention one thing, a way to speed initialization up:

The external 1PPS pulse-train is taken as gospel. If one counts local

40 MHz oscillator cycles between any adjacent pair of 1PPS events, one will get a very accurate measurement of the local oscillator signal frequency. Knowing that it is supposed to be 40 MHz, one can compute how far off correct (as a ratio) that local oscillator is from truth. This can be used to jump far closer starting frequency to correct without waiting for convergence to get there.

Joe Gwinn

lørdag den 23. juli 2022 kl. 21.00.37 UTC+2 skrev Joe Gwinn:

yeh, get an initial guess and then switch to a slow correction so any jitter on the 1pps gets "filtered"

This initial measurement stands alone, not refining a previous body of measurement knowledge, so it's reasonable to set the gain high. Human perception does this a lot. If you hear two sounds a certain interval apart, your hearing is pre-primed to expect a third at exactly the same interval. If the third comes slightly early or slightly late, slightly quieter or slightly louder, we jump to conclusions very quickly about what's happening. Very rapid model-forming, and adapting new sensations to refine the model. Very necessary for a prey animal!

Is there a name for this idea in filter terminology?

Clifford Heath

There are two answers, depending on which field you mean, biology or electronics.

In biology, it has been long known that the brain creates a model of the world, and keys on deviations between prediction and actual. But this isn't just for expected rhythm, it's far more general and flexible than that.

With the speedup algorithm I mentioned earlier, the mechanism is designed with considerable domain knowledge in hand. The primary driver is to achieve robustness despite the imperfections of real clocks et al. The continuous look-ahead algorithm is not flummoxed by non-stationary and/or non-Gaussian probability-distributions, et al. But it's more in the nature of a control system than a filter per se.

Joe Gwinn

A control system also models the plant, measures deviations from the prediction, before it applies a loop filter to decide the corrective step.

That's the filter I'm referring to. It's just the same pronciple with the human system as when synchronising two clocks.

Clifford Heath

On a sunny day (Sun, 24 Jul 2022 08:40:28 +1000) it happened Clifford Heath <no snipped-for-privacy@please.net wrote in <1704967e2e98d7c6$38$2251891$ snipped-for-privacy@news.thecubenet.com>:

No sure, but this is related to 'the alien problem' from cryptography. It goes like: Alien comes to earh, wants to take all knowledge humans have back home. So he gets Encyclopedia Britannica, but it is too heavy and does not fit in his flying saucer. So he writes the text out as an ASCII hex number and does 1 / that number. then he takes a stick and puts a mark on it in that ratio and takes the stick back home.

To say 3 ticks is all you need to convey all information in the universe given time has no granularity. The stick in that example does of course have, limited by size of atoms etc, But does time have granularity?

I use this all the time.

Time is thought to have a granularity of sorts, about 10^-43 seconds, which is a Planck Unit.

.

Joe Gwinn

Well, yes, but we're being a bit pedantic here. The problem is that the word "filter" can have multiple meanings. Like the low-pass loop filter in a PLL or FLL. In the algorithm described earlier, the FLL loop filter is implicit in the choice of look-ahead and cycle times.

Joe Gwinn

Joe Gwinn

On a sunny day (Sun, 24 Jul 2022 12:09:21 -0400) it happened Joe Gwinn snipped-for-privacy@comcast.net wrote in snipped-for-privacy@4ax.com:

Sure but there is a problem, if you scroll down on that site you find the sentence "the Planck time is the time required for light to travel the distance of 1 Planck length in a vacuum". That leads to a circular reasoning, as traveling half a Planck length would take half the time... Just before that the text goes into Planck length, and says in some theories with more dimensions that length is smaller than the fundamental Planck length So much twenty-first century physics assumptions... Start of big bang start of time, obvious bull. Maybe there are a zillion bangs like there are a zillion stars and something that formed those over time. Measurement limits like saying length in feet or whatever ... But sure, what we can measure, being made of matter, probably has a limit. Wait till they figure out gravity.. I still like Le Sage's model as it provides a MECHANISM for gravity. Now they are stuck looking for dark matter..

Very interesting, physics, BTW.