Reasons for quality variation across Freeview channels?

On Tue, 28 Jul 2009 20:54:52 +0000, Richard Tobin wrote:

Things will almoist certainly improve after the switchover - the power
is increasing from 800W to 15kW. But that's more than 3 years away.

And not to mention all the B grade (or should that be Z grade?) movies which
he will miss on Zone Horror if he does not get a Freesat or FTA receiver.

"J G Miller" wrote in message
news
On Tue, 28 Jul 2009 20:54:52 +0000, Richard Tobin wrote:

Things will almoist certainly improve after the switchover - the power
is increasing from 800W to 15kW. But that's more than 3 years away.

And not to mention all the B grade (or should that be Z grade?) movies
which
he will miss on Zone Horror if he does not get a Freesat or FTA receiver.


But many are great cos they are so badly made

Steve Terry

Well, I'll leave the experts on channels to give you the reasons for the
losses, but I'd definitely check your move six inch problems out, more
likely to be pick up on the cable to the aerial, in my experience.

I'm not sure whether the kind of tree matters except that if its in leaf
its going to have a bigger effect I'd imagine, andwhen it blows in the wind
all sorts of strange filtering effects can change dynamically. You do not
say where your aerial is, and if its a dedicated one for the new channels or
if its outside or loft mounted. Certainly, loft mounted ones are affected by
the rain as tiles change their attenuation a lot when wet.

Brian

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"Jonathan Campbell" wrote in message
...
I'm attempting to form a model of quality variation across Freeview
channels. Maybe 'channel' isn't even the correct term. Could someone point
me at a simple introduction to Freeview's use of wavelength bands and
encoding within bands (grasping for the correct terms)?

I use very few channels, BBC4, Dave, Dave +1, ITV4 mostly. Sometimes BBC1,
2, ITV1, C4, C5 to record (on a cheap Wharfendale receiver / hard-disc
recorder).

I am unaware of BBC1, 2, or 4 ever breaking up; or Dave, Dave +1.

C5 is almost never watchable; ITV4 sometimes breaks up; last week an ITV1
recording was totally unwatchable. Incidentally, C5 is the weakest
analogue channel too, but I think that is common.

Apart from C5, I think I can link the worst occurrences of poor reception
with heavy rain showers between me and the transmitter.

Just to confuse matters further, I had bad problems with ITV4 which seemed
to be cured simply by moving the receiver/recorder six inches. I had
suspected a SCART connection problem, but I'm now inclined to think that
moving the device has some effect on the RF connection (from the aerial).
But the major variability seems to be independent of the device position.

I'm 90% confident of the rain shower hypothesis, that C5 is always
unwatchable, and that BBC1, 2, 4 are always okay.

My original Freeview receiver (not the recorder) told me I had a signal
strength of 9/10. I cannot find any indication of signal strength on the
current machine.

In case it matters, I'm in Derry, Londonderry, about 20 miles from the
Limavady transmitter; definitely not in line of sight. I have a tree that
is roughly in line and just about the same height as my aerial and about
20 metres away. However, I don't think the wetness of the tree has any
effect, nor the density of foliage (it is a sycamore --- deciduous).

TIA,

Jon C.

--
Jonathan Campbell www.jgcampbell.com BT48, UK.

With regard to the sat, if you have a garden, it may be possible to have the
dish fairly low on an outbuilding, but of course the geometry of things and
the tree factor may then be a problem.

Brian

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graphics are great, but the blind can't hear them
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"Jonathan Campbell" wrote in message
...
Richard Tobin wrote:
In article ,
Jonathan Campbell wrote:

I am unaware of BBC1, 2, or 4 ever breaking up; or Dave, Dave +1.

These channels are on multiplexes 1, B, C and D which use 16QAM.

C5 is almost never watchable; ITV4 sometimes breaks up; last week an
ITV1 recording was totally unwatchable. Incidentally, C5 is the weakest
analogue channel too, but I think that is common.

These are on multiplexes 2 and A which use 64QAM.

If your signal is poor, reception is much less robust on multiplexes
using 64QAM. So what you report is not surprising. You probably need
a better aerial.

See http://www.ukfree.tv/txdetail.php?a=IC711296 for more information
about your transmitter.


Thanks, that site and the information you give are most helpful and
informative --- just what I wanted.

Incidentally, as a post on the website mentions, the aerial location on
the map is incorrect; it is at least four times further from
Derry-Londonderry than indicated. It is interesting how far west it
reaches --- I thought my friends in Donegal were dreaming when they
claimed to receive Freeview.

Also, just in case readers think my aerial installation is really bad,
Derry is notoriously difficult for TV reception. We have the Sheriff's
Mountain transmitter no more than four miles from my house, yet nearly
everyone in this area uses Limavady --- except, I see out of my window, a
house opposite. (I realise Sheriff's Mt. will not have digital until the
last moment.) As the map shows, there are parts of the city that cannot
receive Limavady. In fact, there are houses in the low-lying southern part
of the city that seem to have monstrous aerials pointing at Strabane ---
but maybe that is historical legacy.

I have little doubt that my cabling, at least, could be improved.

Should I be thinking of a Freesat dish? One problem I can see with that is
that the dish would have to be fitted to the front of the house.

Best regards,

Jon C.

--
Jonathan Campbell www.jgcampbell.com BT48, UK.

Brian Gaff wrote:
Well, I'll leave the experts on channels to give you the reasons for the
losses, but I'd definitely check your move six inch problems out, more
likely to be pick up on the cable to the aerial, in my experience.

I'm not sure whether the kind of tree matters except that if its in leaf
its going to have a bigger effect I'd imagine, andwhen it blows in the wind
all sorts of strange filtering effects can change dynamically. You do not
say where your aerial is, and if its a dedicated one for the new channels or
if its outside or loft mounted. Certainly, loft mounted ones are affected by
the rain as tiles change their attenuation a lot when wet.


Aerial mounted on the chimney (by a competent aerial man). I'm pretty
sure that the aerial is C/D (i.e. that analogue transmission is C/D) as
required; it is the correct polarisation.

Fitted close to 20 years ago.

I may have introduced losses and noise via a Labgear 'distribution box'
I introduced many years ago mainly so that I could feed a VHF FM radio
aerial onto the same cable.

I no longer use the VHF aerial, so maybe I can remove the distribution box?

Without that distribution box, what is the best method of joining coax.
cable? The cable needs to go to one place only.

As it is, I'm not /yet/ hurting badly enough to think of an aerial +
cable replacement, especially as am also considering Freesat.

But I now know that variation across programme channels is not uncommon.

Regarding Freeesat, I would not even think twice except that the dish
would have to be mounted on the front of the house; there is no line of
sight from anywhere in the back garden or garage or side of the house.
There is no problem however with trees at the front.

Best regards,

Jon C.


--
Jonathan Campbell www.jgcampbell.com BT48, UK.

Jonathan Campbell wrote:

Without that distribution box, what is the best method of joining coax.
cable? The cable needs to go to one place only.


If its inside you could use the normal TV type connectors+Male/male
adaptor, don't use the screw terminal type. A more robust solution is
using satellite F connectors with 'barrel' (male-male connector), but it
can be tricky getting the right connectors for the cable and or you may
need special tools for the better versions.

Outside is more difficult, you need water tight F connectors + self
amalgamating tape, but if you want it to last another 20 years use new
coax CT100/WT100 or similar, by then you may aswell replace the aerial.

--
Tony

Java Jive wrote:
Nonsense, break-up is often caused by impulse interference such as
'dirty' switching by neighbouring central-heating thermostats, the
motor scooters that children have nowadays, etc.

That's true but if our own new aerial had been installed properly with a
balun and masthead amp we would not be suffering impulse interference on
QAM64 muxes just two days after it was installed.

(kim)

IME, masthead amps tend to amplify the unwanted impulse interference
just as much as the wanted signal, though, if you put the signal
through a UHF pass filter first (I believe these are incorporated in
some masthead amps now), at least it is then only amplifying that
portion of the interference that lies within UHF.

All other things being equal, I would suggest choosing a highly
directional aerial, choosing as far as possible a site for it that
doesn't look out over sources of interference such as neighbouring
houses, trying to get it as high as possible, and using
double-screened downlead cable, aerial sockets, and flyleads, are
probably more important.

Also, putting a mains spike suppressor on the power source for the
masthead amp will help reduce the impact of electrical spikes
originating in your own home, though it would be better to remove the
source of the spikes, for example by getting your central heating
serviced, with particular regard to the thermostat. If you can
persuade your neighbours to do likewise, so much the better.

On Fri, 31 Jul 2009 16:13:59 +0100, "kim" wrote:

That's true but if our own new aerial had been installed properly with a
balun and masthead amp we would not be suffering impulse interference on
QAM64 muxes just two days after it was installed.

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Java Jive wrote:
IME, masthead amps tend to amplify the unwanted impulse interference
just as much as the wanted signal,

The problem here is there's a 20 metre run of coax from the (non
balun-fitted) aerial to a ten-way amplifier/splitter mounted on a side wall.
The excess cable run is picking up all the interference from the car park on
its outer braid which is then massively amplified before being split ten
ways. A balun/masthead amp would have avoided much of that.

(kim)

Certainly, if one has to amplify, then doing it as near to the aerial
as possible makes sense, and I do not question the balun either.

However, I would ask: how can you be sure that the interference is
not actually being picked up by the aerial? And if you are certain of
this, is the cabling CAI approved double-insulated, satellite grade,
x100 cabling? Perhaps that would be the first thing to look at?

Is this an installation paid for by a third party, such as a landlord
for a block of flats, or one paid for by you that you can request be
improved?

Perhaps the pro riggers here, I'm not one, will have something
else/better to recommend?

On Fri, 31 Jul 2009 18:29:14 +0100, "kim" wrote:

The problem here is there's a 20 metre run of coax from the (non
balun-fitted) aerial to a ten-way amplifier/splitter mounted on a side wall.
The excess cable run is picking up all the interference from the car park on
its outer braid which is then massively amplified before being split ten
ways. A balun/masthead amp would have avoided much of that.

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