A Sky, cable and digital tv forum. Digital TV Banter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » Digital TV Banter forum » Digital TV Newsgroups » uk.tech.digital-tv (Digital TV - General)
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

TV Freeview picture breaking up, New 4G transmitter and Aeroplanes



 
 
Thread Tools Display Modes
  #11  
Old September 24th 15, 11:01 PM posted to uk.tech.digital-tv,uk.d-i-y
Dave Plowman (News)
external usenet poster
 
Posts: 5,342
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

In article ,
john west wrote:
Suddenly in the last month or so our Freeview television picture is
suddenly breaking up.


We got a visit from the 'at800' Engineer who fitted a filter in-line
before our television aerial amplifier. Apparently we have a new phone
4G transmitter installed quite near.


The engineer said his readings were within accepted limits.


We are about 15 miles north east of Heathrow Airport and get a lot of
planes, they are sufficiently high so that we cannot read the markings
on the planes. We are about thirteen miles north west of the crystal
palace transmitter.


Now every time a plane goes over the picture and sound break up and
that's very often.


Everything worked fine before until about a month or so ago, and we have
carefully checked all connections and leads and have bought a new Aerial.


Any suggestions please.


Is there a signal level indication in the set's menu?

--
*There are two kinds of pedestrians... the quick and the dead.

Dave Plowman London SW
To e-mail, change noise into sound.
Ads
  #12  
Old September 25th 15, 07:36 AM posted to uk.tech.digital-tv,uk.d-i-y
Brian-Gaff
external usenet poster
 
Posts: 576
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

Has somebody built a new high rise or put a crane up somewhere quite close?
Normally the direct signal should more than compensate for any weird
reflections from aircraft. the flutter effect on signals is normally a
problem when its a significant part of the signal.


Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
"john west" wrote in message
...
Suddenly in the last month or so our Freeview television picture is
suddenly breaking up.

We got a visit from the 'at800' Engineer who fitted a filter in-line
before our television aerial amplifier. Apparently we have a new phone 4G
transmitter installed quite near.

The engineer said his readings were within accepted limits.

We are about 15 miles north east of Heathrow Airport and get a lot of
planes, they are sufficiently high so that we cannot read the markings on
the planes. We are about thirteen miles north west of the crystal palace
transmitter.

Now every time a plane goes over the picture and sound break up and that's
very often.

Everything worked fine before until about a month or so ago, and we have
carefully checked all connections and leads and have bought a new Aerial.

Any suggestions please.



  #13  
Old September 25th 15, 07:46 AM posted to uk.tech.digital-tv,uk.d-i-y
Brian-Gaff
external usenet poster
 
Posts: 576
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

Well, in his area the signal strength normally is very high, which was why I
did wonder about new buildings or cranes, as just down the road from my bit
of west London, a bloody great tower block has meant a lot of people
becoming Virgin customers due to apparently poor signal quality, not
strength.


I suppose if he has not replaced the downlead, it could well be that he is
just using a water filled resistor as an aerial. We really need hard figures
etc to be close to a diagnosis.
The channels in use down here seem pretty well away from the 4g stuff and
thought removing said filter as a test might be a valid thing to do. Most
seem to be attenuators at other frequencies as well.
Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
"Bill Wright" wrote in message
...
john west wrote:
Suddenly in the last month or so our Freeview television picture is
suddenly breaking up.

We got a visit from the 'at800' Engineer who fitted a filter in-line
before our television aerial amplifier. Apparently we have a new phone 4G
transmitter installed quite near.

The engineer said his readings were within accepted limits.

We are about 15 miles north east of Heathrow Airport and get a lot of
planes, they are sufficiently high so that we cannot read the markings on
the planes. We are about thirteen miles north west of the crystal palace
transmitter.

Now every time a plane goes over the picture and sound break up and
that's very often.

Everything worked fine before until about a month or so ago, and we have
carefully checked all connections and leads and have bought a new Aerial.

Any suggestions please.


This sounds like a classic case of 'misleading fault reporting', to be
honest. I think you'll find that there's no connection between the planes
and the fault. Please don't be offended, but customers often assign
irrelevant 'causes' to their reception faults. It can be anything from the
weather, 'the number of aerials sucking on it', the radio ham across the
road coming home from work, next door's dog barking and the noise
affecting the waves, pretty well owt really.

Planes take a while to pass over when they're high up. How does that fit
in with the picture break up? What about the planes you don't see? Any
break up when you can't see any planes?

But assuming you aren't simply having a laugh it might be interesting to
discuss the scenario you describe.

Planes so high up will probably be in an area of relatively low field
strength, so any reflections (which might have a rapid additive and
subtractive effect on the signal output of your aerial) will be similarly
reduced in strength. Beam tilt at the tx is the reason for this. Apart
from the obvious reasons for beam tilt there's the fact that such high
powered tx's aren't allowed to radiate much above the horizon because of
the possibility of EMI in aeroplanes.

Yes, 'aeroplane flutter' was an issue in the analogue days, very rare
under circumstances such as yours for UHF but quite common for VHF. The
main reason for this is that UHF aerials are far more directional than VHF
ones. Indeed some types of VHF aerial had no discrimination whatsoever
against signals from above (anyone like to name two examples, one of each
polarisation?)

Any reflection from a high plane would arrive sufficiently delayed for the
modulation system in use by digital TV to ignore it (it's expressly
designed to do just that), unless it was so strong that it confused the
receiver's AGC. And that's impossible, really, because your aerial will be
discriminating against the reflection by 10 or 20dB (which is a lot.)

It isn't possible that any interference actually generated by the plane
will affect your reception. Think what a fuss there's be near airports if
that was the case!

When you say you've bought a new aerial, well, buying the thing is only a
small part of the process! Is it the right type, pointing the right way?
Any obstructions? And there are other things. Just because you've had good
reception until now doesn't mean thing really. I'm guessing that the
signal from your aerial is marginal, and something is causing occasional
break up.

I must apologise for the length of this reply but it's either skulk in
here or talk to a damnfool friend of my wife who's called round seemingly
to get us to join the Green Party. I just don't want to cause an upset. .
.

Bill



  #14  
Old September 25th 15, 08:20 AM posted to uk.tech.digital-tv,uk.d-i-y
Big Les Wade
external usenet poster
 
Posts: 9
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

Bill Wright posted
john west wrote:
Suddenly in the last month or so our Freeview television picture is
suddenly breaking up.
We got a visit from the 'at800' Engineer who fitted a filter in-line
before our television aerial amplifier. Apparently we have a new phone
4G transmitter installed quite near.
The engineer said his readings were within accepted limits.
We are about 15 miles north east of Heathrow Airport and get a lot
of planes, they are sufficiently high so that we cannot read the
markings on the planes. We are about thirteen miles north west of the
crystal palace transmitter.
Now every time a plane goes over the picture and sound break up and
that's very often.
Everything worked fine before until about a month or so ago, and we
have carefully checked all connections and leads and have bought a
new Aerial.
Any suggestions please.


This sounds like a classic case of 'misleading fault reporting', to be
honest. I think you'll find that there's no connection between the
planes and the fault. Please don't be offended, but customers often
assign irrelevant 'causes' to their reception faults. It can be
anything from the weather, 'the number of aerials sucking on it', the
radio ham across the road coming home from work, next door's dog
barking and the noise affecting the waves, pretty well owt really.


So it could be the planes then?


Planes take a while to pass over when they're high up.


But they aren't, he's only 15 miles from Heathrow. They're probably only
a few thousand feet up.

How does that fit in with the picture break up? What about the planes
you don't see? Any break up when you can't see any planes?

But assuming you aren't simply having a laugh it might be interesting
to discuss the scenario you describe.

Planes so high up


They're not so high up.

will probably be in an area of relatively low field strength, so any
reflections (which might have a rapid additive and subtractive effect
on the signal output of your aerial) will be similarly reduced in
strength. Beam tilt at the tx is the reason for this. Apart from the
obvious reasons for beam tilt there's the fact that such high powered
tx's aren't allowed to radiate much above the horizon because of the
possibility of EMI in aeroplanes.

Yes, 'aeroplane flutter' was an issue in the analogue days, very rare
under circumstances such as yours for UHF but quite common for VHF. The
main reason for this is that UHF aerials are far more directional than
VHF ones. Indeed some types of VHF aerial had no discrimination
whatsoever against signals from above (anyone like to name two
examples, one of each polarisation?)

Any reflection from a high plane


They're not high.

would arrive sufficiently delayed for the modulation system in use by
digital TV to ignore it (it's expressly designed to do just that),
unless it was so strong that it confused the receiver's AGC. And that's
impossible, really, because your aerial will be discriminating against
the reflection by 10 or 20dB (which is a lot.)

It isn't possible that any interference actually generated by the plane
will affect your reception. Think what a fuss there's be near airports
if that was the case!


You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"? Which
is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?

When you say you've bought a new aerial, well, buying the thing is only
a small part of the process! Is it the right type, pointing the right
way?


He said "Everything worked fine before until about a month or so ago".
So unless somebody's knocked the aerial it must be pointing the right
way.

Any obstructions? And there are other things. Just because you've had
good reception until now doesn't mean thing really. I'm guessing that
the signal from your aerial is marginal, and something is causing
occasional break up.


I have had exactly the same problem as him, and my set is showing 100%
signal strength from the nearby transmitter. The picture was fine for a
couple of years, then for a few months it was awful, and now it's fine
again. No LOS obstructions have appeared or disappeared and we've
changed nothing in the setup. It can only be the transmitter.

--
Les
  #15  
Old September 25th 15, 08:37 AM posted to uk.tech.digital-tv,uk.d-i-y
Mark Carver
external usenet poster
 
Posts: 7,633
Default TV Freeview picture breaking up, New 4G transmitter andAeroplanes

On 25/09/2015 09:20, Big Les Wade wrote:

You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"? Which
is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?


Because of the way COFDM modulation (used for digital TV and DAB) works,
you effectively have interleaved data (with forward error correction),
spread over a few thousand separate carriers occupying almost 8 MHz (for
TV) of spectrum. Any reflection (at any given moment) will only cancel a
small selection of those carriers.


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #16  
Old September 25th 15, 09:02 AM posted to uk.tech.digital-tv,uk.d-i-y
The Natural Philosopher[_2_]
external usenet poster
 
Posts: 639
Default TV Freeview picture breaking up, New 4G transmitter andAeroplanes

On 25/09/15 09:20, Big Les Wade wrote:
Which is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?


Sorry, that is a binary mindset.

Aircraft and indeed everything that moves causes interference with TV
signals.

The point is that modulation techniques are designed, in the case of
digital, to instead of 'slowly degradewith interference' to have enough
error correction so that signals don't degrade at all under light
interference, but degrade massively once the error correction is
overwhelmed.

So its perfectly reasonable to say that light moving ghosting from
aircraft on an analogue TV signal would be no obstacle to decent digital
transmissions.



--
Global warming is the new Margaret Thatcher. There is no ill in the
world it's not directly responsible for.
  #17  
Old September 25th 15, 09:23 AM posted to uk.tech.digital-tv,uk.d-i-y
[email protected]
external usenet poster
 
Posts: 45
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

In uk.d-i-y Mark Carver wrote:
On 25/09/2015 09:20, Big Les Wade wrote:

You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"? Which
is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?


Because of the way COFDM modulation (used for digital TV and DAB) works,
you effectively have interleaved data (with forward error correction),
spread over a few thousand separate carriers occupying almost 8 MHz (for
TV) of spectrum. Any reflection (at any given moment) will only cancel a
small selection of those carriers.

We have a boat moored at Gallions Point Marina, right under the flight
path into London City Airport. OK, we *are* very close to the
aircraft when they land but they certainly do break up the signal
(both vision and sound) on our Freeview TV. It's not just a minor
hiccough either, the sound goes off and the picture breaks up and
freezes for the few seconds while an aeroplane goes over. It is only
a few seconds though.

--
Chris Green
·
  #18  
Old September 25th 15, 09:49 AM posted to uk.tech.digital-tv,uk.d-i-y
Mark Carver
external usenet poster
 
Posts: 7,633
Default TV Freeview picture breaking up, New 4G transmitter andAeroplanes

On 25/09/2015 10:23, wrote:
In uk.d-i-y Mark Carver wrote:
On 25/09/2015 09:20, Big Les Wade wrote:

You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"? Which
is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?


Because of the way COFDM modulation (used for digital TV and DAB) works,
you effectively have interleaved data (with forward error correction),
spread over a few thousand separate carriers occupying almost 8 MHz (for
TV) of spectrum. Any reflection (at any given moment) will only cancel a
small selection of those carriers.

We have a boat moored at Gallions Point Marina, right under the flight
path into London City Airport. OK, we *are* very close to the
aircraft when they land but they certainly do break up the signal
(both vision and sound) on our Freeview TV. It's not just a minor
hiccough either, the sound goes off and the picture breaks up and
freezes for the few seconds while an aeroplane goes over. It is only
a few seconds though.


Yes, that doesn't surprise me, a plane very low will be reflecting
enough stuff back with a large aperture to 'punch out' enough of a mux
for a few seconds as it passes over.

As ever with all digital reception issues the only viable method to
see what's going on is with a spectrum analyser.

Mr Wright of both these parishes has published work on the effect
on reception of windfarms, which is a related subject of course.

http://www.wrightsaerials.tv/services/interference-studies/television_interference_studies_for_wind_turbine_i nstallations.pdf




--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #19  
Old September 25th 15, 11:09 AM posted to uk.tech.digital-tv,uk.d-i-y
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

In article , Bill Wright
wrote:
This sounds like a classic case of 'misleading fault reporting', to be
honest. I think you'll find that there's no connection between the
planes and the fault.


You and others may be correct to dismiss the idea. But I'm not so sure as
I've not yet done the maths. However...

It occurred to me that the large path difference combined with the high
velocity might phase and amplitude fluctuate the received signal fast
enough to confuse any mpx correction. The situation could combine large
dopplers with large delays that change fast.

Planes take a while to pass over when they're high up. How does that fit
in with the picture break up? What about the planes you don't see? Any
break up when you can't see any planes?


It may depend on where the planes are, and what their velocity is if the
above speculation is relevant. No idea if it is at present.

Another possible problem is this group's old friend, "Digital Cliff".

So 4G might be enough to tip something over such a cliff for all I know.
Given millions of receivers someone somewhere could draw the short straw.
8-]

Anyone done any estimates on the effects I outline?

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #20  
Old September 25th 15, 11:13 AM posted to uk.tech.digital-tv,uk.d-i-y
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default TV Freeview picture breaking up, New 4G transmitter and Aeroplanes

In article , Mark Carver
wrote:
On 25/09/2015 09:20, Big Les Wade wrote:


You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"?
Which is it; interference from planes can happen, or it can't? Why
would householder fussing prevent interference to the digital signal
but not to the analogue signal?


Because of the way COFDM modulation (used for digital TV and DAB) works,
you effectively have interleaved data (with forward error correction),
spread over a few thousand separate carriers occupying almost 8 MHz (for
TV) of spectrum. Any reflection (at any given moment) will only cancel
a small selection of those carriers.


Erm... within a set of limits and assumptions.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT. The time now is 01:31 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.SEO by vBSEO 2.4.0
Copyright 2004-2018 Digital TV Banter.
The comments are property of their posters.