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Rebuilding a 1995 GPS Time Server so I don't get Telstra'd

2026-09-05 | original

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Why This Matters

A hobbyist restored a 1995 TrueTime XL-AK GPS time server by fitting it with a Raspberry Pi 5 and GNSS HAT to create a modern stratum 1 NTP server, complete with working vintage LCD and status LED. The project is framed against a real-world incident where a similar GPS time server took down Australia's cell service for 12 hours, underscoring how fragile and critical timing infrastructure is. It shows accurate local time sources can now be built for well under $100.

Key Takeaways

A failing GPS time server knocked out Telstra's cell service for 12 hours, highlighting timing as a single point of failure in modern networks.
A Raspberry Pi 5 (even the 1GB, $44 model) plus a GNSS HAT and Chrony is enough to run a stratum 1 NTP server for a small network.
Vintage hardware can be 'restomodded' — the build reuses the 1995 chassis, 16x2 LCD, and bicolor LED, with plans to join the NTP Pool.

Worth a Look

Raspberry Pi 5 (4GB) — This is the exact brain Jeff dropped into the vintage TrueTime chassis to turn it into a stratum 1 NTP server. With a GNSS HAT stacked on top, the Pi 5 handles chrony, the LCD, and status LED duties in one tidy board — and it's just as happy running your own home lab projects.

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Rebuilding a 1995 GPS Time Server so I don't get Telstra'd

In June I purchased this TrueTime XL-AK time server, so I could learn more of the history of GPS-based time.

I received it on June 22, and just 16 days later a similar GPS time server took down Australia's cell service for 12 hours! I made a short video about it but put off digging into the TrueTime... until now.

Over the past couple weeks, I've 'restomodded' this device with a Raspberry Pi, to build a stratum 1 NTP Time server, which I'd like to eventually add to the NTP Pool. I found a way to drop in a Pi 5 and GNSS HAT, display the time and GPS status on the built-in 16x2 LCD, show the status on the bicolor LED, and make this box useful again.

I lay out more of the hardware details in today's YouTube video:

But in this post, I'll show how I configured the Raspberry Pi to work as a stratum 1 NTP time server with:

Jimmy Paputto's L1 GNSS HAT

Chrony (for time synchronization and NTP services)

Time and Daytime Protocols

A Densitron LCD built into the TrueTime XL-AK

... continue reading

Explore topics: truetime xl-ak raspberry pi 5 gps time server chrony ntp pool