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

Luc Brosens dvb at bsc-bvba.be
Tue Nov 20 17:55:54 CET 2007



P. van Gaans wrote:
> On 11/18/2007 10:34 AM, Luc Brosens wrote:
>> 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
>>
>> _______________________________________________
>> linux-dvb mailing list
>> linux-dvb at linuxtv.org
>> http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
>>
> 
> Which motherboard do you have? And you've got a clean picture without
> blocks with the offical Dutch/Flemish Mediaguard CAM? You would be the
> first. (see http://linuxtv.org/wiki/index.php/KNC1_TV-Station_DVB-S )
> 
> Can you reproduce the descrambling, are you sure VTM was not temporarily
> unscrambled?
> 
> P.
> 
(I hate being the first one ...)

my current motherboard is a ASUS M2N-MX (the one with the defective PCI slot was a ASUS M2NPV-VM, which had the benefit of a HDTV-capable DVI-port)
yes, I have had a perfect picture on several channels now : VTM, VT4, KANAAL2 and even Private Spice
each time, I only let it run for a minute or so, as I'm trying to get the tuning working consistently
for now, it's a crap shoot : at most 1 in every 20 attempts succeeds in obtaining a FE_HAS_LOCK

I don't think that the channel was temporarily unscrambled, as I got the message "Received new PMT - sending to CAM"
also, every lock I get on a scrambled signal gives me a clear picture, each time
it's just extremely difficult to get a lock (I've had about a dozen locks until now, on that 4 channels)

it's strange : both szap and gnutv_if_no_CAM lock in a split second, gnutv_with_CAM fails miserably

I was thinking of tweaking gnutv, so that it first obtains the tuning lock and only then attempts to access the CAM
what do you think ?

Luc



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