[linux-dvb] Strange DVB-T using scan and tzap FEC and Guard interval problems

Simon G linuxtv at simong.net
Wed Sep 26 21:55:09 CEST 2007


Hi,

Our DVB-T network has once more been changed here in Karlstad, Sweden.
Once more I noticed strange behaviour with scan (atrpms linuxtv-dvb-apps
ver 1.1.1.2_20070420.fc7) and tzap. It used to work without a problem
before.

After creating a scan file with fec high, low and guard interval set to
auto I was able to scan a Mux for channels and create a channels.conf. I
knew the frequency(650MHz), the bandwidth(8MHz), the modulation (QAM64)
and the transmission-mode (8k).
However in trying to use the resulting channels.conf with tzap, I never
get a lock. I didn't know the FEC or guard interval part.

Now I have 2 different types of DVB-T cards. One Nova T 500 PCI
Dib0700(Yes I know, I have the latest firmware) and a TerraTec Cinergy
1200 DVB-T (SAA7146)

Using my favorite card (the 1200) i tried a frequency search in MythTV
using one of the mux frequencies and the other bits I knew. No luck :(
Then I tried the same using the Nova T 500. Yes it found and locked to
channels !

Anyway to cut a long story even longer ;) ...

I read the resulting entries in the mythtv database and edited my
channels.conf then tzap worked with both cards ??

scan was saying ...
SVT1:650000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_4:HIERARCHY_NONE:1019:1018:1010

when MythTV and tzap needed ...
SVT1:650000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_2_3:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:1019:1018:1010

ie. FEC_2_3 and GUARD_INTERVAL_1_8 were needed for tzap and MythTV using
scan again with a few -vvv gave this ...

parse_terrestrial_delivery_system_descriptor:498: 0x3184/0x3fd
650000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_4:HIERARCHY_NONE

ie. the wrong?? FEC and GUARD interval

Anybody know whats going on here ?? Is the network sending wrong info ??

Thanks,

Simon G.






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