Re: Yawn - more on Freeview reception

Thank you for this helpful reply.

I was just reply up above and stating someone had told me much the same
thing about power increase etc when analogue goes. Also they mentioned
about mux and high-end ones not fairing as good.

I have an aerial installed by an aerial rigging firm (you have to trust
'em). The cable was replaced, although I was told it wasnt brilliant so
I will look at that.

Thanks again.


Nigel Cliffe 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.


So, how to fix things ?
1) improve the down-lead from the aerial. If its been there a while, chances
are its not really up to the job. Use certified PF100 lead (big B&Q
branches sell it in sealed rolls if you cannot find it anywhere else).
2) consider changing the aerial, though just installing the biggest
wide-band aerial isn't necessarily going to improve things. I'd probably go
with a certified Band-B for that transmitter unless local aerial specialist
on the ground advised otherwise.


Hmmmm, when the analogue signal is switched off it is not being
replaced by anything much better (ie good signal without interference
or lost reception) is it.

When analogue goes off, there are two things which will happen at the same
time. Firstly the power of the digital output can be increased. And
secondly, the frequencies used for digital can be moved around to optimise
reception.
However, I am skeptical about this fixing all the problems people face;
there are so many very iffy analogue aerials around (you see them bent,
pointing the wrong way, etc, etc), that those are likely to have lots of
problems with digital, yet get a "sort of, if snowy" analogue picture.


So does anyone truly know why this problem cannot be sorted for us
folk with Freeview.
Is it too much to ask.

I fear the problems you experience are going to be all too common over the
next few years, and nothing compared to those who suddenly discover their TV
doesn't work when analogue switch-off happens.



- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

.

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