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

["Mark Edwards" <mark@edwards.homelinux.net>]

Thanks Hamish - I'll reply inline...
----- Original Message ----- 
From: "Hamish Moffatt" <hamish@cloud.net.au>
To: <linux-dvb@linuxtv.org>
Sent: Friday, January 30, 2004 12:26 AM
Subject: [linux-dvb] Re: [YET-ANOTHER-UPDATE] Avermedia HOWTO


>
> 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).
>

I hear you, although I am not sure that I am employing such a strict
definition in my use of the word "demultiplex". By my use of this word I am
trying to communicate the fact that a number of disparate signals are
"carried" on a single "transport" frequency. I am not saying how. You are
right to request a clarification I guess, but I am not sure if a more
appropriate word exists. If you can suggest one, please be my guest...

> >    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.
>

I don't think a detailed expose of heterodyne receiver technology is
appropriate here, but I think that we could improve the wording - "extract"
is just so.... non-technical... ;-)

> >    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.

Did they? Shows you how much time I spend watching SBS doesn't it! ;-)

>
> > 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.

Confession - I wrote the first version of this HOWTO before I really had a
full and deep understanding of what PIDS really were and how they were being
used. You're right, the broadcasters swing the PIDS around willy-nilly
depending on which way the wind is blowing. Question really is, is a full
copy of my channels_dot_conf really appopriate for this document and does it
really help to get things going...

I appreciate your feedback... It'll be in the next version...

Cheers,

Mark (ex G1KSP)

>
> > 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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>




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