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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.

Freeview interference question



 
 
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  #1  
Old December 29th 06, 05:01 PM posted to uk.tech.digital-tv
Vaughan
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Posts: 65
Default Freeview interference question

My sister recently had a new aerial installed in order to start receiving
Freeview (there was no aerial at all beforehand).

Due to the height of the roof and its design the rigger installed the aerial
in the loft. The aerial is a high gain and the loft is high up (second
floor). The signal strength and quality on Freeview channels is 100 percent,
according to the TV's menu system.

My sister lives in south Bucks in a border area between the London and
Meridian regions, so there's a choice of receiving signals from either
Crystal Palace or Hannington. The aerial rigger pointed the aerial toward
Crystal Palace, as most people in the area seem to do this. NB the
topography of the area is a bit difficult for TV reception so the rigger
installed a masthead amp on the aerial.

All is well apart from intermittent dropouts in the digital stream - my
sister said that the picture occasionally freezes or the sound drops out.
She wasn't sure on what channels this was happening so I went round and
checked - the fault mostly occurs on the ITV/C4 mux and occasionally on the
mux that carries BBC3 and BBC2.

It seems to happen once every hour or so but it is annoying. I'm sure it's
some kind of local interference rather than the TV because the fault occurs
when viewing on both the TV and DVD recorder's Freeview tuners. The flylead
is new and the coax from the aerial to the TV is probably about thirty years
old - it was preinstalled when the house was built and connects the aerial
point up to the loft. Maybe it needs replacing?

I know that the ITV mux is the weakest so I expected the bulk of the
problems to be on those channels. I tried switching the central heating on
and off and also the lights but that didn't affect it. However the electric
power shower caused major breakup, so at least I've isolated one problem. It
was only when I was driving home that I remembered that she had just
installed a new cordless phone. Could this be the cause of the intermittent
breakup? I think she has a base station and two handsets.

Hopefully if the phones are causing the problem they can be set to operate
on different channels, and maybe I should re-site the base unit.

If it's not the phone is there anything else I should be looking out for and
are there any filters I could install?

Is it worth experimenting by swinging the aerial to point at Hannington
(some locals do this as they prefer the local news from there and not
London). I assume the signals from Hannington would be on different
frequencies than Crystal Palace, so perhaps they would not suffer the same
interference.

Thanks in advance.


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  #2  
Old December 29th 06, 05:14 PM posted to uk.tech.digital-tv
Bill Wright
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Posts: 8,408
Default Freeview interference question


"Vaughan" wrote in message
. uk...
My sister recently . . .


There's every chance that the old cable will pick up interference caused by
mains switching transients, but since there's a masthead amp the effects of
this will be reduced. The aerial itself will be very vulnerable to such
interference. It could be coming from the other end of the street,
unfortunately. These faults are generally broadband rather than peaking on a
particular frequency, although if anything they will be worse on the lower
channels. The severity of their effects is mostly related to the strength of
the incoming signal and the error correction (16 or 64 QAM).

It might be worth running a temporary CT100 (etc) downlead from the aerial
to the TV set (just run it down the stairs). And when the new downlead is in
place try removing the masthead amplifier. You might get a surprise.
Sometimes a masthead amp can allow impulse interference to have a greater
effect.

Some receivers are better than others at dealing with very short duration
high intensity interference.

Bill


  #3  
Old December 30th 06, 01:30 AM posted to uk.tech.digital-tv
John Porcella
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Posts: 1,632
Default Freeview interference question


"Vaughan" wrote in message
. uk...
My sister recently had a new aerial installed in order to start receiving
Freeview (there was no aerial at all beforehand).

Due to the height of the roof and its design the rigger installed the

aerial
in the loft. The aerial is a high gain and the loft is high up (second
floor). The signal strength and quality on Freeview channels is 100

percent,
according to the TV's menu system.

My sister lives in south Bucks in a border area between the London and
Meridian regions, so there's a choice of receiving signals from either
Crystal Palace or Hannington. The aerial rigger pointed the aerial toward
Crystal Palace, as most people in the area seem to do this. NB the
topography of the area is a bit difficult for TV reception so the rigger
installed a masthead amp on the aerial.


Hmm, firstly he put the aerial inside the building, rather than at roof
level which would cut the signal strength, due to the lesser height and
attenuation by the roof material, which then justifies having having to
boost the signal which he deliberately weakened!

The fact that the roof is high is treated as a disadvantage rather than an
advantage!! He needs a longer ladder or a cherry picker.



Is it worth experimenting by swinging the aerial to point at Hannington
(some locals do this as they prefer the local news from there and not
London). I assume the signals from Hannington would be on different
frequencies than Crystal Palace, so perhaps they would not suffer the same
interference.


I suspect that getting the aerial higher up will lessen any interference
from the cordless telephone.


--
MESSAGE ENDS.
John Porcella


 




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