[linux-dvb] CAM inserted/used reduces signal and SNR ?

Luc Brosens dvb at bsc-bvba.be
Sun Nov 18 10:34:57 CET 2007


Hi,

side note :
the problems in my previous post "KNC1 TV-Station S, revision 0x1894, doesn't tune", were related to the PCI-slots of the motherboard I used
rebuilt the machine around a new motherboard, both KNC1's are now recognized and able to tune
lesson learnt : check the hardware before complaining about the software ...

next step is accessing the scrambled signals

as I said, the cards scan OK and using "szap" I can tune to them :
mythtv at silverstar:~> szap -a 1 -c channels.conf VT4
reading channels from file 'channels.conf'
zapping to 795 'VT4':
sat 0, frequency = 12669 MHz V, symbolrate 22000000, vpid = 0x03af, apid = 0x039b sid = 0x31e5
using '/dev/dvb/adapter1/frontend0' and '/dev/dvb/adapter1/demux0'
status 05 | signal 9ffb | snr 21f6 | ber 0000ea08 | unc 00000000 |
status 1f | signal d430 | snr dad3 | ber 00000100 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d47e | snr dab5 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d5b8 | snr dacd | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d458 | snr dac7 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d5bc | snr daf7 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d460 | snr da9a | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d47c | snr daac | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d46c | snr dac1 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d465 | snr dabe | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d481 | snr dabb | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d46f | snr dab5 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d43b | snr daa0 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d468 | snr dabe | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d47e | snr daa6 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d342 | snr dac1 | ber 00000000 | unc 00000000 | FE_HAS_LOCK

mythtv at silverstar:~> szap -a 1 -c channels.conf VTM
reading channels from file 'channels.conf'
zapping to 793 'VTM':
sat 0, frequency = 12669 MHz V, symbolrate 22000000, vpid = 0x03ad, apid = 0x0399 sid = 0x31e3
using '/dev/dvb/adapter1/frontend0' and '/dev/dvb/adapter1/demux0'
status 1f | signal d404 | snr b772 | ber 0000c000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d479 | snr da8b | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d5b7 | snr daac | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d5b6 | snr da97 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d47c | snr daa0 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d5bb | snr da70 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d342 | snr da97 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d480 | snr daa6 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d340 | snr da97 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d481 | snr da40 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d47e | snr da6a | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d340 | snr da6d | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal d468 | snr da91 | ber 00000000 | unc 00000000 | FE_HAS_LOCK

both VTM and VT4 are encrypted channels here, so no mpg-output at this time

I have found one (1) encrypted channel that works using gnutv :

mythtv at silverstar:~> gnutv -adapter 1 -channels channels.conf -out dvr VTM
Using frontend "ST STV0299 DVB-S", type DVB-S
status SCVYL | signal d47c | snr dac1 | ber 0000ff00 | unc 00000000 | FE_HAS_LOCK
CAM Application type: 01
CAM Application manufacturer: 0100
CAM Manufacturer code: 0000
CAM Menu string: CANALDIGITAAL
CAM supports the following ca system ids:
  0x0100
Received new PMT - sending to CAM...
mythtv at silverstar:~>

using mplayer, I have a clear picture
this proves to me that descrambling works

but I have yet to find another channel that works, even on the same transponder frequency none of the others work !?

what's more, it looks like it's the CAM that's the cause of things :

first, remove the CAM from the CI slot :

mythtv at silverstar:~> gnutv -adapter 1 -channels channels.conf -out dvr VT4
Using frontend "ST STV0299 DVB-S", type DVB-S
status SCVYL | signal d464 | snr da9a | ber 0000a700 | unc 00000000 | FE_HAS_LOCK

the lock is immediate

insert the CAM, same command :

mythtv at silverstar:~> gnutv -adapter 1 -channels channels.conf -out dvr VT4
Using frontend "ST STV0299 DVB-S", type DVB-S
CAM Application type: 0140 | snr 83c1 | ber 0000ff00 | unc 00000000 |
CAM Application manufacturer: 0100
CAM Manufacturer code: 0000
CAM Menu string: CANALDIGITAAL
CAM supports the following ca system ids:er 0000ff00 | unc 00000000 |
  0x0100
mythtv at silverstar:~>  c82e | snr a15e | ber 0000ff40 | unc 00000000 |

so gnutv accesses the CAM, and the signal and SNR drop to unusable levels ?

the same happens for unencrypted channels : the signal and SNR drop if a CAM is present and gnutv is used

NO CAM :
mythtv at silverstar:~> gnutv -adapter 1 -channels channels.conf "BBC World"
Cannot open decoder; defaulting to dvr output
Using frontend "ST STV0299 DVB-S", type DVB-S
status SCVYL | signal ccf4 | snr d6b6 | ber 0000ff00 | unc 00000000 | FE_HAS_LOCK

INSERT CAM :
mythtv at silverstar:~> gnutv -adapter 1 -channels channels.conf "BBC World"
Cannot open decoder; defaulting to dvr output
Using frontend "ST STV0299 DVB-S", type DVB-S
CAM Application type: 0156 | snr 81ed | ber 0000ff00 | unc 00000000 |
CAM Application manufacturer: 0100
CAM Manufacturer code: 0000
CAM Menu string: CANALDIGITAAL
CAM supports the following ca system ids:er 0000ff38 | unc 00000000 |
  0x0100
mythtv at silverstar:~>  bcc0 | snr a05f | ber 0000ff18 | unc 00000000 |


szap is not bothered by the presence of a CAM (because it doesn't access it ?), tuning works fine with and without one

questions :

why does inserting and accessing a CAM reduce the signal and SNR levels ? (even if no descrambling is needed, as for BBC World)
how can this be solved ?
anyone out there having the same problems ?

thanks,

Luc



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