[Gllug] [OT] TFT displays

[Chris Hunter]

Adam Bower wrote:

> I have read that they are not broadcasting the new digital channels from
> any transmitters at anything like full power yet, apparently due to the
> risk of causing problems with the analogue channels+interference but
> once the switch over is underway then digital power will be boosted when
> the analogue is turned off.

No - digital TV requires very much less power than analogue.

> Indeed if I compare (perhaps incorrectly, I am not a radio engineer) the
> numbers for Crystal Palace on these 2 pages (first is Analogue, 2nd is
> Digital).
> 
> http://www.bbc.co.uk/reception/transmitters/tv_trans/tv_crystal.shtml
> http://www.dtg.org.uk/retailer/tx_lse.html
> 
> It seems like Crystal Palace is a whopping 1000kW for analogue and each
> digital multiplex gets 20kW... of course not all things are equal. Any
> radio engineers like to explain this?

See above - analogue broadcasting (both of radio and TV) require much 
more power than digital for the same area coverage.  The problem with 
analogue is always signal-to-noise ratio - VHF and UHF signals always go 
to the horizon, irrespective of power.  A low power signal will have a 
very poor S/N ratio at distance - higher power just improves S/N 
(increasing useful range).  The S/N ratio required for digital reception 
is MUCH smaller than that required for analogue.

> (If I compare Talcolneston in East Anglia which is where my television
> comes from right now it claims 250kW for Analogue and 10kW or 5kW for
> the digital channels.)

That's about right, based on the S/N requirements for each.

Chris

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