The five multiplex (Cambs & Beds).

On Tue, 23 Jun 2009 17:16:25 GMT, Paul Ratcliffe
wrote:

On Mon, 22 Jun 2009 23:02:37 +0100, Scott wrote:

Have you tried without the booster? I thought boosters were a bad
idea for digital and also that the connection from aerial to decoder
should be uninterrupted.

Both are myths spread by the ignorant.

I am happy to accept that I am ignorant, but there are others on the
group who have also expressed concerns about the use of aerial
amplifiers. As you clearly regard yourself as an expert, would you
care to enlighten us all on the subject?

"Scott" wrote in message
...
On Tue, 23 Jun 2009 17:16:25 GMT, Paul Ratcliffe
wrote:

On Mon, 22 Jun 2009 23:02:37 +0100, Scott
wrote:

Have you tried without the booster? I thought boosters were a bad
idea for digital and also that the connection from aerial to decoder
should be uninterrupted.

Both are myths spread by the ignorant.

I am happy to accept that I am ignorant, but there are others on the
group who have also expressed concerns about the use of aerial
amplifiers. As you clearly regard yourself as an expert, would you
care to enlighten us all on the subject?

AFAIK the main concern with amplifiers is the noise they introduce to the
signal path - I asked about this in an earlier post but the only reply I got
was someone answering my question with a question.

On Tue, 23 Jun 2009 19:39:21 +0100, Scott wrote:

On Tue, 23 Jun 2009 17:16:25 GMT, Paul Ratcliffe
wrote:

On Mon, 22 Jun 2009 23:02:37 +0100, Scott wrote:

Have you tried without the booster? I thought boosters were a bad
idea for digital and also that the connection from aerial to decoder
should be uninterrupted.

Both are myths spread by the ignorant.

I am happy to accept that I am ignorant,

I wasn't necessarily meaning you. You are probably just repeating what
you heard from a bloke who "knows" about these things.

but there are others on the group who have also expressed concerns
about the use of aerial amplifiers.

Properly used they are a benefit and in some cases an absolute necessity.
Wrongly used they make virtually no difference or in some cases make
things worse.

As you clearly regard yourself as an expert, would you care to enlighten
us all on the subject?

See my other post. To summarise, you need to get the most signal out of
the sky you can, to give adequate margin before distribution, using an
appropriate aerial.
When distributing, you need to take account of the losses involved in
doing so and amplify BEFORE you lose the signal.
Amplification adds noise and amplifies the noise that is already there
as well as the signal.

"Paul Ratcliffe" wrote in message
...
On Mon, 22 Jun 2009 22:46:38 +0100, ian field

wrote:

Its a single house installation specifically ordered from the rigger to
be
DVB-T compatible, an 8.6dB 6 way splitter/booster was added at the bottom
of
the downlead to serve several rooms.

There is no point putting a booster at the bottom if the problem is lack
of signal. It needs to go at the top. If you just need to split, then you
must have adequate signal level first.

A second booster was added some months ago when there was poor signal on
the multiplex carrying the ITV channels, that was left in place after the
signal improved again, but more recently the multiplex carrying Five and
Virgin1 has become weak, the booster was then replaced with one having
higher gain (16.8dB) that improved reception slightly but it varies from
perfectly OK one day to fluctuating wildly the next.

Added where?
Increasing gain doesn't generally increase receive margin, especially if
put in the wrong place.

You need to get levels measured at the top and then work out where to go
from there.

The aerial riggers that put up the freeview aerial damaged the roof which
then leaked causing extensive water damage indoors - I'm very reluctant to
send anymore expensive cowboys up there!

A few months ago there was a problem with the multiplex carrying the ITV
channels, that cleared up so I must have a magic aerial that goes bad (but
only for one multiplex at a time) for a few weeks then comes good again, now
its the multiplex carrying Five that's fine one day and flaky the next -
maybe there's a gremlin up there with a box of wave traps deciding which
multiplex to pick off next.

People are still asking me about the trees in the signal path days after I
pointed out there are none.

"Paul Ratcliffe" wrote in message
...
On Mon, 22 Jun 2009 22:46:38 +0100, ian field

wrote:

Its a single house installation specifically ordered from the rigger to
be
DVB-T compatible, an 8.6dB 6 way splitter/booster was added at the bottom
of
the downlead to serve several rooms.

There is no point putting a booster at the bottom if the problem is lack
of signal. It needs to go at the top. If you just need to split, then you
must have adequate signal level first.

A second booster was added some months ago when there was poor signal on
the multiplex carrying the ITV channels, that was left in place after the
signal improved again, but more recently the multiplex carrying Five and
Virgin1 has become weak, the booster was then replaced with one having
higher gain (16.8dB) that improved reception slightly but it varies from
perfectly OK one day to fluctuating wildly the next.
It sounds increasingly dreadful.

Bill

"Paul Ratcliffe" wrote in message
...
On Tue, 23 Jun 2009 19:39:21 +0100, Scott
wrote:

On Tue, 23 Jun 2009 17:16:25 GMT, Paul Ratcliffe
wrote:

On Mon, 22 Jun 2009 23:02:37 +0100, Scott
wrote:

Have you tried without the booster? I thought boosters were a bad
idea for digital and also that the connection from aerial to decoder
should be uninterrupted.

Both are myths spread by the ignorant.

I am happy to accept that I am ignorant,

I wasn't necessarily meaning you. You are probably just repeating what
you heard from a bloke who "knows" about these things.

but there are others on the group who have also expressed concerns
about the use of aerial amplifiers.

Properly used they are a benefit and in some cases an absolute necessity.
Wrongly used they make virtually no difference or in some cases make
things worse.

As you clearly regard yourself as an expert, would you care to enlighten
us all on the subject?

See my other post. To summarise, you need to get the most signal out of
the sky you can, to give adequate margin before distribution, using an
appropriate aerial.
When distributing, you need to take account of the losses involved in
doing so and amplify BEFORE you lose the signal.
Amplification adds noise and amplifies the noise that is already there
as well as the signal.

I'll give you an example that I saw this very day. The scene is a communal
OAP centre with 40 bungalows on the site. The communal ae is on Emley, and
had perfect LOS until a large steel framed building started to go up about
100 yards away. It's one of those new polyclinics. The steel frame being
complete, the contractors started on Friday to install wire mesh safety
barriers on each level. These almost reach each ceiling. The movement of the
crane gave the problem an interesting dynamic quality. Unsurprisingly
reception at the centre was affected. In fact signal levels dropped by about
28dB. This meant that the levels available at each bungy were about 20dB
below threshold and were also covered in amplifier noise. There was also
some multipath. The residents had no real reception, just very snowy
analogue. On Saturday the son of one old lady came round for his weekly
visit. Seeing the telly he went off somewhere and bought one of those
dreadful set-back amps with the curious curved case and the variable gain
control. This had no beneficial effect whatsoever. With the gain down the
snowy analogue picture was slightly more snowy; with it up it had a strange
grainy pattern. He took it back to the shop and they tested it, and refused
a refund, saying that it was unsaleable as he had destroyed the bubble pack
(how else to get it out?). He re-installed it at mother's. I went along
today (called out today) and discovered what the problem was with the
system. Whilst I was on the phone discussing things with the landlord this
chap came and asked me to check his mother's reception. I'd added enough
amplification to get the levels correct at the bungys (though not at the
head-end input of course) as a temporary measure. At mother's the analogue
was present but a bit snowy, and it kept fading. The digi was hopeless. I
explained the problem and said that we would be either bringing in the
signal from elsewhere by underground cable, or possibly using a different
transmitter, but that either would not happen overnight. At this he said
that he wanted the landlord to reimburse him for the cost of the splendid
booster. I advised him to write to them, but expressed the view that he was
wasting his time.

Once the signal/noise ratio is poor you can't improve it by amplification.
In fact you can only make it worse. If amplification appears to improve
reception is is because the device following the 'booster' is 'deaf' --
insensitive or noisy.

Bill

"ian field" wrote in message
...
People are still asking me about the trees in the signal path days after I
pointed out there are none.

You have to be patient with us. Some of us are getting on a bit you know.

"I said there aren't any trees!"
"Fleas? No, there aren't any fleas. Not on me anyway."

Bill

In article , ian field gangprobing.al
scribeth thus

"Paul Ratcliffe" wrote in message
...
On Mon, 22 Jun 2009 22:46:38 +0100, ian field

wrote:

Its a single house installation specifically ordered from the rigger to
be
DVB-T compatible, an 8.6dB 6 way splitter/booster was added at the bottom
of
the downlead to serve several rooms.

There is no point putting a booster at the bottom if the problem is lack
of signal. It needs to go at the top. If you just need to split, then you
must have adequate signal level first.

A second booster was added some months ago when there was poor signal on
the multiplex carrying the ITV channels, that was left in place after the
signal improved again, but more recently the multiplex carrying Five and
Virgin1 has become weak, the booster was then replaced with one having
higher gain (16.8dB) that improved reception slightly but it varies from
perfectly OK one day to fluctuating wildly the next.

Added where?
Increasing gain doesn't generally increase receive margin, especially if
put in the wrong place.

You need to get levels measured at the top and then work out where to go
from there.

The aerial riggers that put up the freeview aerial damaged the roof which
then leaked causing extensive water damage indoors - I'm very reluctant to
send anymore expensive cowboys up there!


Well many aerial riggers go up on roof's every day and don't have those
problems, and if they do their insured against such damage .. I presume
matey wasn't?..

A few months ago there was a problem with the multiplex carrying the ITV
channels, that cleared up so I must have a magic aerial that goes bad (but
only for one multiplex at a time) for a few weeks then comes good again, now
its the multiplex carrying Five that's fine one day and flaky the next -
maybe there's a gremlin up there with a box of wave traps deciding which
multiplex to pick off next.


Something is not right up there, it could be water in the co-ax cable,
an open circuit cable, a short circuit cable .. something frequency
selective.

What you need is a good well equipped experienced rigger to put this
balls up right!..

People are still asking me about the trees in the signal path days after I
pointed out there are none.


OK .. well that rules out the number one cause then. Any large buildings
or things like cranes around?....
--
Tony Sayer

"tony sayer" wrote in message
news
In article , ian field gangprobing.al
scribeth thus

"Paul Ratcliffe" wrote in message
...
On Mon, 22 Jun 2009 22:46:38 +0100, ian field

wrote:

Its a single house installation specifically ordered from the rigger to
be
DVB-T compatible, an 8.6dB 6 way splitter/booster was added at the
bottom
of
the downlead to serve several rooms.

There is no point putting a booster at the bottom if the problem is lack
of signal. It needs to go at the top. If you just need to split, then
you
must have adequate signal level first.

A second booster was added some months ago when there was poor signal
on
the multiplex carrying the ITV channels, that was left in place after
the
signal improved again, but more recently the multiplex carrying Five
and
Virgin1 has become weak, the booster was then replaced with one having
higher gain (16.8dB) that improved reception slightly but it varies
from
perfectly OK one day to fluctuating wildly the next.

Added where?
Increasing gain doesn't generally increase receive margin, especially if
put in the wrong place.

You need to get levels measured at the top and then work out where to go
from there.

The aerial riggers that put up the freeview aerial damaged the roof which
then leaked causing extensive water damage indoors - I'm very reluctant to
send anymore expensive cowboys up there!


Well many aerial riggers go up on roof's every day and don't have those
problems, and if they do their insured against such damage .. I presume
matey wasn't?..

A few months ago there was a problem with the multiplex carrying the ITV
channels, that cleared up so I must have a magic aerial that goes bad (but
only for one multiplex at a time) for a few weeks then comes good again,
now
its the multiplex carrying Five that's fine one day and flaky the next -
maybe there's a gremlin up there with a box of wave traps deciding which
multiplex to pick off next.


Something is not right up there, it could be water in the co-ax cable,
an open circuit cable, a short circuit cable .. something frequency
selective.

What you need is a good well equipped experienced rigger to put this
balls up right!..

People are still asking me about the trees in the signal path days after I
pointed out there are none.


OK .. well that rules out the number one cause then. Any large buildings
or things like cranes around?....
--
Tony Sayer




Nope.

Something is not right up there, it could be water in the co-ax cable,
an open circuit cable, a short circuit cable .. something frequency
selective.

What you need is a good well equipped experienced rigger to put this
balls up right!..

People are still asking me about the trees in the signal path days after I
pointed out there are none.


OK .. well that rules out the number one cause then. Any large buildings
or things like cranes around?....
--
Tony Sayer




Nope.



Well in the absence of any further info and the reluctance to get a
proper rigger to have a look I don't quite know what else to advise.
Except adding amplification is very likely to make this worse. In fact
where we live some 18 miles from the 'heath we've had to put a small
attenuator (device for reducing the signal) into the line to the
distribution amplifier input this was so as to stop the much stronger
analogue signals causing intermodulation and spurious signals across the
band!..
--
Tony Sayer