[AMRadio] Re: GB> Re: IARU bandplan


Bry Carling bcarling at cfl.rr.com
Sat Oct 13 18:20:48 EDT 2007


Yeah, but as great as digital TV may sound we had ALL KINDS of
trouble with it over a 12 month trial period here from our cable
provider and finally we gave up.

It was constantly going bad, de-synchronising the audio and 
video or stuttering or stopping completely.  Also, it took 
several seconds to change channels every time. What 
a hassle! I hated digital TV!

We dumped digital cable and went back to analog.

> 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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