Steve is correct.
The modulation is linear with 8 level vestigial sideband transmission
(the carrier( at -11 dB from peak sideband power) is only .3 Mhz from
the lower edge of the channel) and uses a 3-2 data rate allowing a
19.39 megabit data stream to be sent in a 6 mcs bandwidth
channel. That channel can contain an eclectric mix of video, audio,
data with high quality audio channels up to near 20 kcs bandwidth
each. The present system is very inefficient, the AM video modulates
only 87.5% negative while the sync and 1/2 the color burst modulate a
maximum of +15% positive. Even the audio is 25 kcs deviation as
compared to the75 kcs used in bcst FM radio with the resultant lower S/N in TV.
Here is a good link.
It was definitely time for a change and the large screen multichannel
audio system here proves it. I basically have a movie theater for TV at home.
Like it or not the world is going digital (modulation) but actually
the digital TV transmitter is a linear AM system.
Larry
W3LW
At 05:00 PM 10/13/2007, you wrote:
[EMAIL PROTECTED] writes:
> The spectral footprint of the analog station is going to be reduced from
> 6MHz down to around 200kc... and there are already some stations in San
> Antonio that are broadcasting in Digital, with channels like (channel 4
> being the 'main') 4.1, 4.2, 4.3, etc...
I don't think so. HDTV takes up the full 6 MHz channel for one giant data
stream. That data can be multiplexed, divided, into more channels,
IF you don't
want it to be high-resolution. The overall spectrum savings, as I understand
it, comes from rearranging the stations' channel assignments to better "pack"
them in.
Steve WD8DAS
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