I stumbled across this product listing:
https://www.teradak.com/products/115.html
It's a Pi hat that contains two TCXOs, one at 19.2 MHz for the CPU and
one at 25 MHz for the Ethernet controller. It's a rather permanent
modification, as you have to desolder the stock crystals and replace
them with wires going to the hat. I'm not 100% sure how to order the hat
yet, but they gave a price of $46 (USD) via email.
I'm curious if this would provide any meaningful improvement in system
clock accuracy, for NTP, if I'm already a GPS PPS hat. If there's a
reasonable chance this could be interesting, I'm thinking about ordering
a couple and "sacrificing" a Pi 3 and/or Pi 4.
In terms of mounting both hats, I'm guessing that the TCXO is only using
power from that hat connector, so rather than use the hat connector, I
would just solder some wires to it and the Pi, such that I could stack
the TCXO on top of the GPS hat physically but not need to connect them
electrically.
Richard
=====================================
Richard,
As a pure sacrificial experiment I would be interested to know your results.
In terms of NTP time keeping, I'm not sure you would gain a lot. Best
results here are obtained when the RPi is kept at a steady or very slowly
changing temperature. I have one which is in a normally closed cupboard
butting onto a north-facing outside wall:
https://www.satsignal.eu/mrtg/raspi1_ntp.html
and this is a Raspberry Pi 1 model B. By contrast, here's one sitting near
a central heating radiator:
https://www.satsignal.eu/mrtg/raspi12_ntp.html
which is an RPi 3 model B. Both have a constant CPU load (light on RasPi-1,
14% average on RasPi-12. Both have GPS/PPS sources attached.
Given that the path to the outside Ethernet world on both of those models is
via a USB controller, I would expect to see very little improvement with a
TCXO in a constant temperature environment. Just perhaps with a RasPi-4 you
/might/ see an improvement as the Ethernet has a more direct path, but
that's a board where self-generated heat is greater, so the thermal issues
might make things worse.
Try it and see!
Cheers,
David
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: [email protected]
Twitter: @gm8arv
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