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Robustness of Freeview HD vs SD



 
 
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  #1  
Old November 22nd 16, 08:49 AM posted to uk.tech.digital-tv
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Posts: 264
Default Robustness of Freeview HD vs SD

So "Author" blew down our TV antenna and we've had to resort to an indoor
portable antenna until its fixed. Curiously not a single HD channel now works
on my Humax box, yet most of the SD channels are perfectly ok. I live in London
so I presume both are broadcast from Crystal Palace so I can only assume
either that:

1) HD is broadcast at a lower power than SD or
2) The error correction on HD isn't as good as that of SD.

Can anyone think of any other reasons what the issue might be?

--
Spud

  #4  
Old November 22nd 16, 09:54 AM posted to uk.tech.digital-tv
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Default Robustness of Freeview HD vs SD

On Tue, 22 Nov 2016 10:43:20 +0000
David Woolley wrote:
On 22/11/16 09:49, d wrote:
Can anyone think of any other reasons what the issue might be?


3) HD is transmitted with a larger constellation (256QAM v 64QAM (or
even QPSK for the local stuff)), so has a lower noise margin between
signalling states (6dB worse).

4) HD is transmitted with a lower guard interval, so is less tolerant of
multipath (1/128 v 1/32).


That doesn't sound like a particularly well designed system for when the
inevitable switch off of SD happens. If some people already have marginal SD
reception they might as well give up on HD altogether.

5) There may be selective fading for the particular frequency at your
site (which may be different for the portable antenna).


Possibly.

--
Spud

  #5  
Old November 22nd 16, 12:17 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
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Posts: 420
Default Robustness of Freeview HD vs SD

On Tuesday, 22 November 2016 09:49:28 UTC, wrote:
So "Author" blew down our TV antenna and we've had to resort to an indoor
portable antenna until its fixed. Curiously not a single HD channel now works
on my Humax box, yet most of the SD channels are perfectly ok. I live in London
so I presume both are broadcast from Crystal Palace so I can only assume
either that:

1) HD is broadcast at a lower power than SD or
2) The error correction on HD isn't as good as that of SD.

Can anyone think of any other reasons what the issue might be?

--
Spud


See below re possible differences in broadcast power.

The higher symbol rate of HD requires a lower S/N ratio.
  #6  
Old November 22nd 16, 01:04 PM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 6,505
Default Robustness of Freeview HD vs SD

In other words yes.
I do not have a box for hd yet, but will need one if the current plans of
squashing stuff into fewer channels does go ahead of course.
Its actually a lot more difficult to set up an indoor aerial on digital
than on analogue as there is noo real time way to check for multipath etc,
that often bugs indoor aerials.

Sometimes a couple of bits of wire on the end of a length of coax sticky
taped to a window in roughly the right direction workds far better than an
indoor aerial. I'm convinced many of these are a con job.
Brian

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"David Woolley" wrote in message
news
On 22/11/16 09:49,
d wrote:
So "Author" blew down our TV antenna and we've had to resort to an indoor
portable antenna until its fixed. Curiously not a single HD channel now
works
on my Humax box, yet most of the SD channels are perfectly ok. I live in
London
so I presume both are broadcast from Crystal Palace so I can only assume
either that:

1) HD is broadcast at a lower power than SD or


Only true for some of the commercial multiplexes. Main channels are all
200kW.

2) The error correction on HD isn't as good as that of SD.


They seem to have the same error correction rate for the main channels
(2/3).


Can anyone think of any other reasons what the issue might be?


3) HD is transmitted with a larger constellation (256QAM v 64QAM (or even
QPSK for the local stuff)), so has a lower noise margin between signalling
states (6dB worse).

4) HD is transmitted with a lower guard interval, so is less tolerant of
multipath (1/128 v 1/32).

5) There may be selective fading for the particular frequency at your site
(which may be different for the portable antenna).



 




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