How to measure DVB-T OFDM

[jkprg]

Hi,

I have a DVB-T modulator PCIe card and I'm feeding it with valid (most of the time) MPEG TS stream but TV can't decode the output. What equipment would you suggest  for DVB-T modulator measurement to check if it's generating correct signal and if not how to find what's wrong with it? I'm not sure if I really need OFDM analysis instrument because those kind of tools (like FSQ or FSV etc.) are usually really expensive ($10+K). Is it the only way? Maybe PSK analysis across all subcarriers would be enough (although thousands of subcarriers will be certainly painful). Maybe USB some spectrum analyzer (or SDR) with software analysis will be enough but I haven't seen any so far.

Thanks for any suggestion.
Best Regards

Jaroslav

[RoGeorge]

I've seen open source projects of DVB-T modulators/demodulators built with nothing but an ADALM-PLUTO.  It's an educational SDR from Analog Devices, open source, of about $100-$200 (IDK the current price) new.

Search for "adalm pluto DVB-T".

Since it's all open source, it can be made to measure whatever you need, in theory.  Not sure if that will help or not, in practice.

[tmbinc]

I'd first make sure that the problem is on the RF/Baseband side, not in the MPEG2 stream. For that I'd probably use a random Linux box with DVB (PC with USB dongle, Dreambox, whatever), and manually tune to the channel (via tzap - https://www.linuxtv.org/wiki/index.php/Zap). If that doesn't work, I'd use a random spectrum analyzer with sufficient sweep/FFT bandwidth to cover the channel bandwidth (i.e. slightly more than what an RTL-SDR can do, though you could sweep there as well) without fancy decoding, and just see if the rough spectrum shape looks like a DVB-T channel. If that's the case (and you still can't lock to it), I'd triple-check the modulation parameters. Only if that still doesn't yield anything I'd dive into the baseband domain. You can do this with gnuradio (https://github.com/gnuradio/gnuradio/tree/master/gr-dtv is a working DVB-T receiver that you could hack to give you the intermediate data to verify).

If locking works, but the TV "doesn't show the channel", I'd use dvbsnoop (http://dvbsnoop.sourceforge.net/) to verify the PAT, PMT, SDT, and maybe record the PES-PIDs and check if it successfully plays back on a PC using VLC, maybe use a commercial MPEG2-TS checker (some of them are really good, and some have demo versions).

[jkprg]

Thank you very much. It seems SDR will be the way to go. I'll have a look at that direction.

BTW does any of those (even expensive HW) OFDM analyzers check orthogonality of subcarriers? Does it make any sense to check the feature when OFDM modulators are digital?