Thanks Hamish - I'll reply inline... ----- Original Message ----- From: "Hamish Moffatt" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> > > > -- > Info: > To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject. > > -- Info: To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject.
