Troubles in SFN network

[kapez]

Dear experts, we have problem with SFN network, in DVB-T broadcasting.


We would like to ask you, how to measurement SFN network, when we have two different suppliers on the same frequency.


Now, we have two different modulators, and synchronization is not satisfied. SFN network is not synchronized. SFN does not working.


We would like to recognize, which supplier is cause interference in to the network.


We tested various transmit signals with different delay 60, 120, 200, 400us, problem is the same.


We attach a spectrum analyzer image, before starting the first and second transmitters.


Thx, for any tips and tricks.

[subway]

Well, SFN only works properly if the transmitter clocks (on the same frequency at least) are in perfect sync and the CP is configured properly for all transmitters. If any transmitters clock is out of line or the CP is incorrect/not sufficient, you will have severe interference. I assume the CP is set correctly on all transmitters.

What type of sync solution are you using? GPS, SyncE, 1588 V2?

Be careful during the measurement, as the R&S analyzers clock needs to be synchronized to the same source as the transmitters, otherwise you will measure false results. The clock/timing accuracy needs to be measured one by one (every time the analyzers clock needs to be on the same source as the transmitter), and you will find which transmitter's clock is out of line. I would also do measurements on the clock sources separately as well, to see if the source itself is at fault/out of line, or the transmitter's PLL/OCXO is at fault.

I dont know at which part, but the maximum allowed frequency and timing errors can be found in the DVB-T2 specifications for sure.

If you have better resolution images, that would be awesome.