[AMRadio] Re: GB> Re: IARU bandplan


Larry Will lhwill at verizon.net
Sat Oct 13 17:16:39 EDT 2007


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:
>ars.w5omr at gmail.com 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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