Symmetricom SyncServer S300
The Symmetricom SyncServer S300 is a dedicated stratum-1 NTP time server that can obtain accurate time from GPS satellites, AM radio signals (DCF, WWVB, JJY), or other NTP servers.
Mine has the optional rubidium oscillator, which keeps the time drift under 6 microseconds per day if the GPS time reference is lost.
The GPS input takes advantage of the fact that the antenna is stationary, so it can focus only on the time part of the GPS signal and average it over many satellites for added accuracy. The S300 requires a 12V GPS antenna.
I use a PCTEL GPS-TMG-HR-40NCM antenna (with built-in 40dB amplifier), mounted on my balcony (facing south), and it works quite well — usually there are about 4-6 satellites visible, which is enough to extract an accurate time signal.
If the GPS antenna is mounted outside (as it should be for best reception), it needs a surge protector in case of any nearby lightning discharges. I use a PolyPhaser IS-MR50LNZ+15, which passes up to 15V DC (needed to power the GPS antenna).
I have modified the S300 to add additional BNC ports for the 10MHz output signal, which I then use as a reference for my test equipment. The unit has no fans, so I added a small USB-powered fan to blow over the power supply section, as it got very hot without it.
If you want to carry out the modification too: compatible BNC ports are Amphenol RF 031-6577, then you only need to connect to the serial console and enter
root eng sys cat "/dev/null && bash" to enter the shell, from where you can run
/sbin/seeprom (select options 40 and 42), where you can enable the 10MHz output and other things.
These are pretty neat little devices, but the software on them is old, so don't expose them to the internet.
- Symmetricom SyncServer S300 datasheet (PDF, 3.6MB)
- PCTEL GPS-TMG-HR-40NCM antenna datasheet (PDF, 167kB)
- EEVBlog Forum: Symmetricom S200 Teardown/upgrade to S250 — this is the thread that initially gave me the idea to add the BNC ports to my S300; the unit discussed there is an older model, but most of the things apply also to the newer unit. Thanks to SoundTech-LG and other participants for all the information!