[linux-dvb] Re: [YET-ANOTHER-UPDATE] Avermedia HOWTO

[Hamish Moffatt <hamish@cloud.net.au>]

Good HOWTO Mark. Just a few corrections on the less important details.

On Thu, Jan 29, 2004 at 09:54:41PM +1100, Mark Edwards wrote:
> 
> HOWTO: Get An Avermedia DVB-T working under Linux
>            ______________________________________________
> 
[...]
>    data stream as you can get. Therefore, an Analogue TV card for
>    a PC has the following purpose:
> 
>      * Tune the receiver to receive a broadcast signal
>      * demodulate the broadcast signal

Yes, the broadcast signal is AM video with an FM audio subcarrier.
The tuner shifts this to a fixed intermediate frequency and the
demodulator produces baseband video & audio.

>      * demultiplex  the  analogue video signal and analogue audio
>        signal  (note some countries employ a digital audio signal
>        embedded  within the modulated composite analogue signal -
>        NICAM.)

Demultiplex is not quite the right word IMHO. Demultiplex implies that
the audio and video signals are mixed in time; they're really mixed in
frequency and both present all the time. The audio is on a subcarrier at
a fixed offset from the video carrier. The audio and video would be
demodulated individually (one is AM and the other FM).

>    The  purpose of a simple budget digital TV card (DVB-T,C or S)
>    is to simply:
> 
>      * Tune the received to receive a broadcast signal.
>      * Extract  the encoded digital datastream from the broadcast
>        signal.

The tuner shifts the frequency to a known RF just like the analogue card,
where you have an MPEG2 bitstream modulated through COFDM. Then you use
a demodulator to recover the bits from the analog COFDM signal.

>    Table 1. Transponder Frequencies Mount Dandenong, Vic, Aus.
>    Broadcaster Channel Frequency
>    ABC         VHF 12  226.5 MHz
>    TEN         VHF 11  219.5 MHz
>    NINE        VHF 8   191.625 MHz
>    SEVEN       VHF 6   177.5 MHz
>    SBS         UHF 29  536.5 MHz

SBS in Melbourne moved to 536.625 MHz a few weeks ago.

> Nine Digital:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QA
> M_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:513:660:10
> 72

These guys seem to have changed their video and audio pids at separate
times in the last 24 hours. Fun! Now 519:720.

> Nine Guide:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_
> 64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:670:1074

514 changed too but I can't remember what to.


Cheers
Hamish
-- 
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>


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