From: "peekay" <[EMAIL PROTECTED]>
> > You have brought out the point that when we > mention "Broadcast" mode > > as in case of Cable TV we actually mean shared > bandwidth. > > > > How about putting some figure in Mbps for this > broadcast mode ? > > Just guessing as a layman. I think it should be at least (4300000)/(3600*3s))*8 = 3.1 mbps. Probably much more than that.
extremely good discussion ..
may i, add, in all humility, and with deference to the experts here :
1. cable tv is still co-axial .. not digital
Co-axial is just a cable type. Ethernet has been used on co-axial also, some may remember the T type joints with BNC connectors and terminators at the end, kind of a token ring, check out a old ISA based ethrnet card and one can see the BNC connector to accomodate co-axial cable. Cable does not determine if it is digital or analog.
2. there is no digital speed on the co-axial for tv
Well there is, which is nearly 30 to 40 Mbps in shared mode, per channel. If we combine more channels more speed.
3. the analogue signal is the carrier
The signal carrier is RF flowing along ("not through" the medium, like in case of electronic signal) the co-axial cable which acts as the RF feeder. Therefore, we measure the signal in dB i.e. SNR - Signal to Noise Ratio. The signal type is analog definitely as long as it is on the co-axial cable.
4. there are 99+ channels on ONE co-axial
Well yes, there are all those channels on ONE feeder.
5. frequencies of the channels are different
Very true, each channel occupies 6 Mhz bandwidth with the center frequencies ranging from 50 Mhz to 864 Mhz. Local cable tv provider can certify this for you.
6. a 'tuner' is used to get the channel of one's choice
Very true again.
7. there is audio AND 'video' data
There is no data in strict sense as long as it is ANALOG that is regular PAL type TV signals. When the contents of a given channel are MODULATED at the HeadEnd i.e at Cable providers premises, then the particular channel carries DIGITAL DATA and is obtained at the customer's premises upon DEMODULATION, yes we are talking of Cable Modem.
8. pic res is 352 x 288 pixels (ugh !)
That is regular TV, not digital data. 30 Mbps can carry a lot.
9. tv delivers (so do webcams, even digital ones .. where the pic IS digitally recorded and can be played back in DVD format too)
Well we are not talking about TV anymore, when we want Internet on Cable TV network we talk about digital data packets inside the shell of analog signal, quite like our regular DIAL-UP modem.
10. non-digital in NOT analogue .. its just non-digital .. like negatives of
photos, older audio casettes/wax/vinyl records, video .. err .. movie films,
video casettes, etc .. even human sound is not 'analogue' .. electronically
that is ! .. it just NOT digital
Well this is again true. But we should remember about MOULATION-DEMODULATION.
Now, I want some one to talk about possible Modulation methods (standards) and Encoding methods (standards) which can provide us this data rate.
Just to provide a clue, we are talking about QAM and MPEG together.
Maybe one of our very learned friends here from a reputed institute will tell us about Error Correction applied in this case ;)
Finally, are we dreaming ?
NO, you can take my word for the same.
with Regards, ASHWIN
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