[Zgemma H9.2S] Using an OpenVix Zgemma as a time server

[topofdamornin2ya]

What type of support thread are you creating?

Support question

What OpenViX Image build number are you using?

6.6.013

Have you tried re-flashing WITHOUT settings restore?

NO

Have you tried re-flashing WITH a settings restore?

NO

Hi.

A friend pointed out to me recently how neat it would be if I could use my Zgemma to serve my home Wi-Fi network as a network time server, using the transponders time signal. He says the accuracy would be much better than going over the internet.

I ssh'd into the box and found that time synching is managed by the busybox binary. Unfortunately, it looks as though the version of busybox in OpenVix 6.6 lacks the server option, so I can't make the time available over the network.

Can anyone tell me what I would have to do to make this work?

Thanks everyone.

 

[Joe_90]

Network time accuracy is far better than using the transponder time. Your friend is misinforming you. Transponder time on satellite is subject to propagation delay of several seconds. Terrestrial multiplexes may be slightly less inaccurate, but are still subject to how accurately the time is set by the broadcaster. The best you could expect is that the various transmitters are synchronised, but not necessarily accurate. The only way to make a home network time server with better accuracy than an NTP pool server is with a GPS receiver providing a PPS to a dedicated linux build on a custom kernel. Search for "building a stratum -1 NTP server on a Raspberry Pi" for ideas.

 

[topofdamornin2ya]

Network time accuracy is far better than using the transponder time.

The only way to make a home network time server with better accuracy than an NTP pool server is with a GPS receiver providing a PPS

I'll pass on what you said. It looks like he thought getting time from a broadcast satellite was the same as getting the time from a GPS satellite.

Just because you mentioned it, and because my Zgemma's the only Linux box I have - could I use it as a host for a GPS receiver providing "PPS"? It has a USB port that I don't use.

 

[Huevos]

I'll pass on what you said. It looks like he thought getting time from a broadcast satellite was the same as getting the time from a GPS satellite.

No. The difference is a GPS satellite has an atomic clock onboard which is responsible for the time signal.

On a DTH satellite the time is just "good enough" for purpose. On the transport stream on each transponder the time will be a bit different. Also, it will be the time when the broadcaster sent the signal, not the current time. Round trip to the satellite is around 100,000 km and that does not happen instantaneously. Also, time between the broadcaster and the antenna that sends to the satellite will take time.

If watch a football match via satellite and listen to the commentary on the radio you will notice the satellite is several seconds behind the radio, hence the invention of sport sync radio.

 

[Joe_90]

I'll pass on what you said. It looks like he thought getting time from a broadcast satellite was the same as getting the time from a GPS satellite.

Just because you mentioned it, and because my Zgemma's the only Linux box I have - could I use it as a host for a GPS receiver providing "PPS"? It has a USB port that I don't use.

Not really. Do an Internet search on using Raspberry Pi as a time server. The kernel build for this will be specific for use with a GPS receiver on-board (as a Hat). You use the Pulse Per Second (PPS) feature of the GPS wired directly into the Pi in conjunction with the serial readout of time to get NTP to set the system time accurate to several microseconds of true UTC as determined by the atomic clocks in the GPS satellites. You could set the time on your Zgemma from the Pi and act as a lower stratum (less accurate) time server. But really, a simple Pi server on your network would be best.

 

[topofdamornin2ya]

I'm not the most technical guy in the world but if I can find the right guide with plenty of pictures I might give this a bash over Christmas. Thanks!