OT: Best time of day/weather conditions to scan Freeview channels?
MM
things. I'm very pleased with my inexpensive "August"
Freeview-on-a-stick for the PC. When is the best time/weather
conditions to scan for channels?
- at night?
- during the day?
- when cloudy?
- when bright and sunny?
I get varying numbers of channels, which I re-scan every few weeks.
Sometimes I only get 52. At other times, like today (overcast, humid)
I've got 65.
MM
Mr. Benn
"MM" <kyli...@yahoo.co.uk> wrote in message
news:l0km06hlkpa75vjho...@4ax.com...
Freeview signals are in the UHF part of the radio spectrum. At these
frequencies, time of day makes no difference to signal propagation. You may
find that weather conditions occasionally affect reception when high
pressure can cause the signals to bounce off the troposphere around 15km
above the earth. This can extend the range of the signals quite a lot.
bod
It's mainly the quality of the aerial and distance from the transmitter
that determines how many channels you get. I get 89 channels from a
stick, from the Iver, Buck's area. I've retuned at different times of
the day, also in different weather, but I always get the same amount.
Maybe, get a better aerial.
Bod
Ian Jackson
<nos...@invalid.invalid> writes
up. UHF signals can be propagated great distances by 'tropospheric
ducting', which is created when the temperature of a layer of air in the
troposphere becomes inverted (becoming hotter higher up). This affects
the density and the water vapour content of the air, and hence its
refractive index. As a result, the TV signal gets trapped in a duct, and
gets gradually bent around the earth's curvature (rather than bouncing).
This may happen very low down - sometimes only a few hundred feet,
especially over the sea in long, hot, calm, high pressure weather
conditions.
http://en.wikipedia.org/wiki/Tropospheric_propagation
http://www.dxinfocentre.com/propagation/tr-modes.htm
--
Ian
Mr. Benn
news:vJO3IOJ0...@g3ohx.demon.co.uk...
Thanks for the clarification Ian.
harry
I have Freesat. None of the above problems. You can fit it yourself
but you need to buy a satellite finder meter. Great pictures + two HD
channels. Just there's the usual crap. Lots of foriegn news
channels if you're into news/politics. Plus usual terrestial channels.
Get pixellating occasionally in snow.
Cynic
Night time and no rain or thunderstorms in the area has the best
chance of the strongest signal with least interference at UHF
frequencies. Cloud cover makes no difference but rain will absorb
some of the signal. The Sun emits radio waves that increase the
background noise slightly.
If you are getting variable results however, it is because the signal
strength is marginal. That can usually be corrected by putting the
aerial in a better position or buying a better aerial (one with more
gain).
Check where your nearest transmitter is (there's a web site that will
tell you - do a search), and try to get the aerial in a position where
it has a "view" of the transmitter that does not pass through nearby
walls - and point a directional aerial at the transmitter. Ensure the
aerial is in the same direction as the polarisation of the transmitter
(horizontal or vertical). I *think* that all freeview transmitters
have vertical polarisation BICBW.
--
Cynic
Cynic
wrote:
>Freeview signals are in the UHF part of the radio spectrum. At these
>frequencies, time of day makes no difference to signal propagation. You may
>find that weather conditions occasionally affect reception when high
>pressure can cause the signals to bounce off the troposphere around 15km
>above the earth. This can extend the range of the signals quite a lot.
You won't be using sky waves for freeview, though one thing I did
forget to mention in my reply is that there is a slight possibility of
interference from French TV transmitters, which *will* depend on
ionospheric propagation - usually worse at night.
The nature of digital TV is such that you cannot see the signal
quality or any interference by looking at the image quality - there is
a sudden change from "perfect" quality to nothing at all, with only a
small band in which the picture frequently pixellates or freezes.
Digital TV also does not tolerate reflections (ghosting) all that
well, so some aerial positions in/on the house will not produce a
stable picture despite showing a very strong signal strength due to
reflections from nearby walls or structures, and a directional aerial
may be needed even in strong signal areas for that reason.
--
Cynic
Fredxx
"Cynic" <cyni...@yahoo.co.uk> wrote in message
news:1ufq0654jo7gmlfmp...@4ax.com...
The Freeview transmitters by and large use the same mast as terestial, and
the same polarisation so they can both be received simultaneously.
As a good rule of thumb, all principal transmitters are of horizontal
polarisation, and relay transmitter providing cover for local communities
are generally of vertical polarisation.
MM
wrote:
As a matter of interest, I only get good reception with my aerial and
the USB stick. That is, the USB stick and/or scanning software must
have some kind of threshold (of reception quality) below which it will
not go. This means that however many channels I can receive at any
particular time (when I re-scan every few weeks), they are, as far as
I can tell, although I do not watch the minor channels all that much,
all high quality with very little pixellation.
And whether I get 52 channels, 64 or anywhere in between, I *always*
get the main ones - BBC One, Two, Three etc, C4, C4+, Film-4 and so
on. To be honest, whether I receive some shopping channel or not
doesn't interest me a great deal.
MM
Mr. Benn
> On Sun, 6 Jun 2010 08:59:27 +0100, "Mr. Benn" <nos...@invalid.invalid>
> wrote:
>
>>Freeview signals are in the UHF part of the radio spectrum. At these
>>frequencies, time of day makes no difference to signal propagation. You
>>may
>>find that weather conditions occasionally affect reception when high
>>pressure can cause the signals to bounce off the troposphere around 15km
>>above the earth. This can extend the range of the signals quite a lot.
>
> You won't be using sky waves for freeview, though one thing I did
> forget to mention in my reply is that there is a slight possibility of
> interference from French TV transmitters, which *will* depend on
> ionospheric propagation - usually worse at night.
As Ian Jackson correctly pointed out, extended propagation of UHF TV signals
is via tropospheric ducting when there is a temperature inversion. This
happens at altitudes of up to 15km but can be much lower. UHF signals
cannot propagate via the ionosphere. They pass straight through it.
Cynic
>As a matter of interest, I only get good reception with my aerial and
>the USB stick. That is, the USB stick and/or scanning software must
>have some kind of threshold (of reception quality) below which it will
>not go.
That is the nature of digital signals in general. The quality is
either good enough to provide a digital datastream with very few
errors, or (below a very sharp threshold) the digital content cannot
be recovered without so many errors that it is useless.
If the signal strength/quality is varying about that theshold, you
will get a period of time during which you get a perfect picture,
followed by a sudden break-up during which there is no picture at all.
>And whether I get 52 channels, 64 or anywhere in between, I *always*
>get the main ones - BBC One, Two, Three etc, C4, C4+, Film-4 and so
>on. To be honest, whether I receive some shopping channel or not
>doesn't interest me a great deal.
Unlike analogue TV, with digital TV several different TV channels
(between 10 to 20 or so) are transmitted on a single UHF frequency.
That's why it is possible to transmit so many more channels - they
still only take up a few UHF frquencies. Each set of TV channels on a
single UHF frequency is called a "mux"
The different UHF muxes are not always all transmitted at the same
power, but one mux of channels might have a transmitter power of
1000W, while another mux might be transmitted using only 100W. You
will usually either get all the channels on a particular mux or you
will get none of them.
Go to this excellent site http://www.ukfree.tv/transmitters.php
Enter your postcode and it will show what transmitter(s) are within
range of your location. Then click on your nearest transmitter, and
it will show you all the muxes that that transmitter carries, together
with the transmitter power for each mux. It will also tell you what
aerial type is needed to receive the signals, and whether to orient it
vertically or horizontally.
It also gives other information about each mux, such as the digital
bit-rate. IIUC, if you divide the bit-rate by the number of TV (not
radio) channels on the mux you will get the approximate bit rate for
each channel. The higher the bit rate the better the picture quality.
I'll take a bet that the channels that you do not always get will all
be on a low-power mux from your local transmitter.
My local transmitter is operating most muxes at very low power until
2012. In addition, its aerial is directional and aimed away from my
location, so I don't get sufficient signal strength without a
multi-element aerial. OTOH my main TV reception is via satellite, and
my freeview receiver is only a backup. Satellite channels are usually
at a higher bit-rate than freeview channels, so the picture quality is
better.
--
Cynic
Cynic
>As a good rule of thumb, all principal transmitters are of horizontal
>polarisation, and relay transmitter providing cover for local communities
>are generally of vertical polarisation.
Interesting - I was not aware of that. Thanks!
--
Cynic
bod
With digital transmissions, you don't get a better picture , you either
get a picture or you don't (picture breaks up).
Bod
Paul Cummins
(Cynic) wrote:
> with digital TV several different TV channels
> (between 10 to 20 or so)
Try between 4 and 7.
--
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981
Cynic
Cummins) wrote:
>> with digital TV several different TV channels
>> (between 10 to 20 or so)
>Try between 4 and 7.
You are correct. I was erroneously including the radio and data
channels as well as the TV channels.
An example from Huntshaw transmitter:
Channel 55 (745.8MHz)
ITV3
QVC
Virgin 1
Bid TV
FIVER
FIVE USA
Quest
SuperCasino
CITV
Teachers' TV
Teletext Holidays
Teletext Casino
1-2-1 Dating
MOBILIZER
TOPUP Stream 1
TOPUP Stream 2,
TOPUP Stream 3,
Smash Hits! Radio
Looks like 10 TV channels and 8 other channels.
--
Cynic
Paul Cummins
(Cynic) wrote:
> >Try between 4 and 7.
>
> You are correct. I was erroneously including the radio and data
> channels as well as the TV channels.
<snip>
> Looks like 10 TV channels and 8 other channels.
Many of those chanels either timeshare, or are just Data/Radio channels. There are
8 streams on the MUX.