Re: Yawn - more on Freeview reception

On Sat, 2 Sep 2006 19:20:36 +0100, "Nigel Cliffe" <me@xxxxxxxxxxx>
wrote:

Badbetty wrote:
Is there anyone [technical] who can explain in simplish terms why it
is that on some stations the signal is fine and on others it is poor ?

I am sure there are zilliogs of discussions about this subject, but
what is testing me is that my Freeview box tells me which transmitter
each signal is coming from and they are ALL coming from the same
transmitter (Emley Moor in West Yorkshire).

So, if they are all coming from the same transmitter, why is there
such a varied strength between channels e.g. ITV, C4 show more or
less always fine but, BBC (any of them) on the other hand is rubbish -
particularly when the trees are in leaf or bad weather :)

Is it how much bandwidth they have in the spectrum or something and
BBC is crap (that's a technical term by the way)

Attempt at not too technical explanation:

There are several things going on, and it depends on details of your
transmitter.

Channels are broadcast in blocks of spectrum, known as group or Mux. BBC
channels are in one group, ITV and Ch4 in another, etc. Where I live, there
are six groups.
These groups may be broadcast at different powers.

Further, these groups are on different wavelengths, or channel numbers. So,
if your old aerial was optimised for the local analogue signals (the "band"
of the aerial), it may not be optimal for digital.

When it rains, or with trees in leaf between you and transmitter, the
signals are reduced. Unfortunately for digital, it tends to be a
all-or-nothing (yes, there is a brief bit where it almost works and you get
blocky picktures).

Local to me, the old analogue aerials are Band-B, but the ITV mux is on a
higher channel number (where band-B aerials are a bit marginal) and at lower
power. So, the old analogue aerials struggle with ITV.

Looking at Elmy Moor's data:
http://www.dtg.org.uk/retailer/tx_n.html
the Mux' are all at the same power. BBC is on Ch 52, which is towards the
high end for a band-B, so there might be a bit of roll-off in the reception
from the aerial.

Which says that Mux D is 4 kW when the others are 10 kW so not the
same power.

Scott
.

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