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Open-sourcing a more precise time appliance

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Re: Open-sourcing a more precise time appliance

#61
post #53

Earlier quoted context omitted.

Which is exactly how the telephone industry has done it for decades, it's called a "building-integrated timing supply", or BITS clock. Typically this is a GPS-referenced clock with a local quartz or rubidium holdover oscillator, and output cards with dozens or hundreds of outputs serving various machines in the office.

Curious, why did telephony require such accurate clocks?

Not in telecommunications, but I do know that there are synchronous comm networks that don’t require any kind of sentinel / delimiter because there is a guarantee that the voltage will agree.

My signals background mostly comes out of music, so somebody else probably has a better answer. But any time you need to convert between digital and analog signals relatively seamlessly, ie, introducing minimal processing overhead, you’re going to run into these kinds of issues. In that regard, you can think of telecoms as a CPU, and just like in a computer, you need a system clock that the entire architecture agrees on.

First likely application that comes to my mind is VoIP.

Re: Open-sourcing a more precise time appliance

#62

A few years back I was interested in microsecond-precise timekeeping. My experience was GPS-backed network clocks were surprisingly cheap - but PTP-aware network switches were surprisingly expensive. And though I thought I could cut the cost of a grandmaster clock from $2000 down to $200, I figured there'd be no point if I then have to connect it to a $20,000 network switch. I wonder how Facebook are connecting their…

I'm curious: what's the use case for microsecond-precise timekeeping?

Re: Open-sourcing a more precise time appliance

#63

A very long time ago , HP made a GPS time card just like this, encased in glass and filled with an inert gas such that if the card was tampered with, it was rendered useless. This prevented someone from faking the time signal.

Someone send one of these to CuriousMarc — he is peerless in working on these vintage high precision test pieces.

Re: Open-sourcing a more precise time appliance

#64
Seiko offers a GPS clock in a conventional-home friendly form factor.

First introduced in 2013, the Seiko Space Link GPS clock has proven to be a global success. It is the world's first clock for home or office use that receives a time signal from a GPS satellite, thus delivering atomic clock precision. It measures time to within one second every 100,000 years. Equally importantly, it can be used anywhere in the world and can be installed in almost any situation, so long as it is around 15 metres or less from the open sky. The technology is beautifully practical. 4 times every day, the clock receives a time signal from the GPS satellite network and, when conditions are ideal, adjusts automatically in around 10 seconds of receiving the signal. Between these signal receptions, a high accuracy quartz movement keeps the clock on time.

Wherever you may need it, Seiko Space Link is there, silently marking the passage of time with an elegance and precision that is redefining the world’s perception of what a clock can be. A new standard of excellence has arrived.

https://www.seiko-clock.com/products.html

Re: Open-sourcing a more precise time appliance

#65
This is a pretty neat thing and kudos for them open sourcing it. Typically, you'd have to hand over $5K - $25K for this card! This can hopefully make them available at a lower price.

I built something similar (although I didn't use a CSAC[1] since it was too expensive but I did have a nice OXCO which is pretty stable. I use a Raspberry Pi to distribute plain old TOD via NTP to my local network, but the 10 MHz output I send to my bench where I can use it for radio projects. It is actually a better clock source (frequency stability wise) than the precision time source in my HP spectrum analyzer but it has worse phase noise (jitter) because it does get corrected by up to +/- 20nS periodically.

[1] Chip Scale Atomic Clock - Microsemi -> Microchip https://www.microsemi.com/product-directory/clocks-frequency...

Re: Open-sourcing a more precise time appliance

#66

What's interesting to me is how the form factor of timing GPS modules has stayed constant over the years. I started my GNSS timing journey with a used Trimble GPS from the 2000s, and it has the same form factor and pinout as the modern multi-constellation timing GPSes from uBlox. I've had a GPS clock going for several years at this point, and without an atomic clock or really any fanciness (just LinuxPPS and Chrony),…

Nice project, I've been working on something similar, but with an Arduino (Adafruit ESP32), an Adafruit GPS featherwing and a RTC. I originally started with a Linux-based solution like yours but no matter what I did I couldn't get the accuracy below about 5ms and my goal is sub-ms (verified with an oscilloscope.)

Re: Open-sourcing a more precise time appliance

#67

Man, tough crowd here. And someone who's been following precise timekeeping tech for 25 years now.. this is really cool! I think it's great some smart engineers have built a new reasonably compact and low cost very precise bit of timekeeping hardware. Thank you for sharing it open source!

I am torn. I absolutely love the technical blog post and the effort that went into open sourcing everything needed to build these devices, but, you know, Facebook. Compliments and respect to the engineers involved for really well done engineering.

Re: Open-sourcing a more precise time appliance

#68

Man, tough crowd here. And someone who's been following precise timekeeping tech for 25 years now.. this is really cool! I think it's great some smart engineers have built a new reasonably compact and low cost very precise bit of timekeeping hardware. Thank you for sharing it open source!

I am torn. I absolutely love the technical blog post and the effort that went into open sourcing everything needed to build these devices, but, you know, Facebook. Compliments and respect to the engineers involved for really well done engineering.

They've built and earned their (negative) reputation. This is cool, but it's like Philip Morris Tobacco Company coming out with a useful home appliance. Uhh....thanks?

Re: Open-sourcing a more precise time appliance

#70
post #62

A few years back I was interested in microsecond-precise timekeeping. My experience was GPS-backed network clocks were surprisingly cheap - but PTP-aware network switches were surprisingly expensive. And though I thought I could cut the cost of a grandmaster clock from $2000 down to $200, I figured there'd be no point if I then have to connect it to a $20,000 network switch. I wonder how Facebook are connecting their…

I'm curious: what's the use case for microsecond-precise timekeeping?

Certain trading operations require it. I think there's even a regulatory under Mifid2, bit I'm not in the know about the legals.
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