TV aerials

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Julian

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Jul 22, 2007, 4:04:15 AM7/22/07
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My house has the TV aerial mounted in the loft, (this was done by the
previous owner) it looks like the one at the bottom of page 326 in the Screw
F catalogue and is described as a professional 16.5db gain for use in fringe
reception areas. We don't live in a 'fringe' area - judging by the looks of
the aerials on other people's chimneys.

On analogue TV Channel 4 is a bit snowy and the rest are OK. On freeview I
can only get 3 or 4 channels, and all the rest are either total crap or
nothing at all.

Here's my questions: How much of an obstacle to the signal is the gable end
of the house? (breeze block and brick outer) Would moving the aerial outside
make a difference to reception ? And/or would fitting a signal booster to
the coax cable solve the problem?

I'm not sure really why the aerial was mounted in the loft in the first
instance - maybe for cosmetic reasons...

Julian.

John

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Jul 22, 2007, 4:53:56 AM7/22/07
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"Julian" <j...@supanet.com> wrote in message
news:3cEoi.1170$ph7...@newsfe5-win.ntli.net...
Perhaps the original owner didn't like working at heights. Incidentally,
this is really good:

http://www.wolfbane.com/cgi-bin/tvd.exe

From your post code it gives the compass setting for the transmitters.


Robin

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Jul 22, 2007, 5:01:52 AM7/22/07
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"John" <Trainin...@gmail.com> wrote in message
news:EWEoi.1786$sI3...@newsfe6-gui.ntli.net...
There are some very knowledgeable and experienced aerial fitters and
other on uk.tech.digital-tv. I have x-posted this there and set
follow-ups.

I think one additional bit of info. they will want is the nature of the
coax fitted. Eg is it thin and brown?

--
Robin


Alan

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Jul 22, 2007, 5:17:49 AM7/22/07
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In message <3cEoi.1170$ph7...@newsfe5-win.ntli.net>, Julian
<j...@supanet.com> wrote

>My house has the TV aerial mounted in the loft, (this was done by the
>previous owner) it looks like the one at the bottom of page 326 in the Screw
>F catalogue

Every edition of Screwfix catalogue is different and unless you buy from
them on a regular basis others may not have the most up to date copy.
The cable ties on page 326 are unsuitable for use as an aerial :)

>and is described as a professional 16.5db gain for use in fringe
>reception areas.

Unless you actually know it is a Screwfix aerial then be aware that you
can get either a group aerial for a limited range of frequencies or a
wideband aerial to accept all frequencies. A group aerial will give a
better performance than a wideband of the same size.

Screwfix tend to only sell wideband aerials..

>On analogue TV Channel 4 is a bit snowy and the rest are OK. On freeview I
>can only get 3 or 4 channels, and all the rest are either total crap or
>nothing at all.

Which channels are totally missing?
http://www.dtg.org.uk/retailer/dtt_channels.html

If you have grouped aerial then it may be unsuitable for digital. In
many areas the same aerial can be used for both analogue and digital but
in other areas a change in aerial is required for digital.

Do you know from which transmitter you are obtaining your signal?
If not put your postcode into
http://www.wolfbane.com/cgi-bin/tvd.exe?

Having found your transmitter go to
http://www.dtg.org.uk/retailer/transmitters.html
and find in one of the pages that are listed by region the same
transmitter.

In one of the tables the aerial group for Analogue (A) is listed and
next to it the aerial group for analogue plus digital (A+D) is listed.
If they are both the same then your existing aerial is probably OK but
if they are different a different aerial may be required.

The missing digital channels and the name of the transmitter may give
clues to which aerial you have. Post back with the transmitter details
and someone should be able to advise.

>
>Here's my questions: How much of an obstacle to the signal is the gable end
>of the house? (breeze block and brick outer) Would moving the aerial outside
>make a difference to reception ? And/or would fitting a signal booster to
>the coax cable solve the problem?

In general, an aerial mounted on the roof is going to be a lot better
than one mounted in a loft.

An aerial booster may help if the signals are marginal but of no use
what so ever if the aerial is incorrect for all the digital MUXs.

If you are thinking of DIY then also consider installing a decent fully
screened down-lead such as CT100 (approved satellite quality cable)
http://www.wrightsaerials.tv/coaxcablequalityhmdim.htm
http://www.amac.f2s.com/cable2


--
Alan
news2006 {at} amac {dot} f2s {dot} com

tony sayer

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Jul 22, 2007, 6:09:43 AM7/22/07
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In article <3cEoi.1170$ph7...@newsfe5-win.ntli.net>, Julian
<j...@supanet.com> writes

Loft aerials have always been troublesome. But we did some work at Band
2 frequencies recently and found a 10 dB difference between inside and
out so you can reckon its worse than that!..
--
Tony Sayer


Andy Hall

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Jul 22, 2007, 6:43:16 AM7/22/07
to

I looked out some figures from an installation I had done a while ago.
In the low end of band V (about 650MHz), my installer measured 17dB
difference with the same antenna installed in the loft vs. it being
about 2m vertically above, outside. He also compared the readings for
the same height outside as the internal fixing, and the difference
between the two exterior readings was about 1.5dB. The equivalent
comparisons at the low end of Band IV (500MHz) were about 15dB inside
to out and at the top of Band V (830MHz) was 21dB.

While only three datapoints, this does suggest that the attenuation is
rather worse than linear with frequency.

I'm told that some building materials have quite a metallic content and
I am sure that this wouldn't help either.

This was all before DTTV, so I don't know what the results for that
would have been like, but I do remember the analyser showing cruddy
results and there was a lot of close distance multipath evident on an
analogue picture.


tony sayer

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Jul 22, 2007, 7:13:37 AM7/22/07
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>> Loft aerials have always been troublesome. But we did some work at Band
>> 2 frequencies recently and found a 10 dB difference between inside and
>> out so you can reckon its worse than that!..
>
>I looked out some figures from an installation I had done a while ago.
>In the low end of band V (about 650MHz), my installer measured 17dB
>difference with the same antenna installed in the loft vs. it being
>about 2m vertically above, outside. He also compared the readings for
>the same height outside as the internal fixing, and the difference
>between the two exterior readings was about 1.5dB. The equivalent
>comparisons at the low end of Band IV (500MHz) were about 15dB inside
>to out and at the top of Band V (830MHz) was 21dB.
>
>While only three datapoints, this does suggest that the attenuation is
>rather worse than linear with frequency.
>
>I'm told that some building materials have quite a metallic content and
>I am sure that this wouldn't help either.

Red tiles have a lot of Iron content..

>
>This was all before DTTV, so I don't know what the results for that
>would have been like, but I do remember the analyser showing cruddy
>results and there was a lot of close distance multipath evident on an
>analogue picture.

Well the attenuation's should be much the same..
--
Tony Sayer

Julian

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Jul 22, 2007, 8:06:04 AM7/22/07
to

"Alan" <junk_...@amac.f2s.com> wrote in message
news:CX9zZjB9...@amac.f2s.com...

> In message <3cEoi.1170$ph7...@newsfe5-win.ntli.net>, Julian
> <j...@supanet.com> wrote
>
>>My house has the TV aerial mounted in the loft, (this was done by the
>>previous owner) it looks like the one at the bottom of page 326 in the
>>Screw
>>F catalogue
>
> Every edition of Screwfix catalogue is different and unless you buy from
> them on a regular basis others may not have the most up to date copy. The
> cable ties on page 326 are unsuitable for use as an aerial :)

It's the current one, but I take your point.


>
>>and is described as a professional 16.5db gain for use in fringe
>>reception areas.
>
> Unless you actually know it is a Screwfix aerial then be aware that you
> can get either a group aerial for a limited range of frequencies or a
> wideband aerial to accept all frequencies. A group aerial will give a
> better performance than a wideband of the same size.
>
> Screwfix tend to only sell wideband aerials..

I'm sure it won't be a Screwfix aerial, because Screwfix didn't exist when
this one was installed! I just wanted to use it as an example of an aerial
with three forward facing 'prongs' (sorry for the untechnical description!)

>
>>On analogue TV Channel 4 is a bit snowy and the rest are OK. On freeview I
>>can only get 3 or 4 channels, and all the rest are either total crap or
>>nothing at all.
>
> Which channels are totally missing?
> http://www.dtg.org.uk/retailer/dtt_channels.html
>
> If you have grouped aerial then it may be unsuitable for digital. In many
> areas the same aerial can be used for both analogue and digital but in
> other areas a change in aerial is required for digital.
>
> Do you know from which transmitter you are obtaining your signal?
> If not put your postcode into
> http://www.wolfbane.com/cgi-bin/tvd.exe?

It would appear that I am 21 miles from Winter Hill xmitter. This makes
sense judging from the direction that the aerial (and the neighbour's) is
pointing.


>
> Having found your transmitter go to
> http://www.dtg.org.uk/retailer/transmitters.html
> and find in one of the pages that are listed by region the same
> transmitter.
>
> In one of the tables the aerial group for Analogue (A) is listed and next
> to it the aerial group for analogue plus digital (A+D) is listed.
> If they are both the same then your existing aerial is probably OK but if
> they are different a different aerial may be required.

Checked this, it's aerial group c/d for both.


>
> The missing digital channels and the name of the transmitter may give
> clues to which aerial you have. Post back with the transmitter details and
> someone should be able to advise.

This one is difficult. Multiplex 1 for sure, but BBC 3 is weak. Multiplex 3
is mostly weak or nothing. A and B is mostly nothing. C is good. D is mostly
nothing. I've noticed that dry high pressure days in winter seem to allow a
better picture than wet summer ones.

>
>>
>>Here's my questions: How much of an obstacle to the signal is the gable
>>end
>>of the house? (breeze block and brick outer) Would moving the aerial
>>outside
>>make a difference to reception ? And/or would fitting a signal booster to
>>the coax cable solve the problem?
>
> In general, an aerial mounted on the roof is going to be a lot better
> than one mounted in a loft.
>
> An aerial booster may help if the signals are marginal but of no use what
> so ever if the aerial is incorrect for all the digital MUXs.
>
> If you are thinking of DIY then also consider installing a decent fully
> screened down-lead such as CT100 (approved satellite quality cable)
> http://www.wrightsaerials.tv/coaxcablequalityhmdim.htm
> http://www.amac.f2s.com/cable2
>

Thanks for your help. I'm thinking that I need to mount the aerial outside
and use some decent cable. Cable won't be easy because most of it is buried
beneath the plaster :-(

I think it may be easier to get a professional in to sort it out, I'm
struggling to understand it all fully!

Julian,


rob...@invalid.invalid

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Jul 22, 2007, 10:45:42 AM7/22/07
to

>
>It would appear that I am 21 miles from Winter Hill xmitter. This makes
>sense judging from the direction that the aerial (and the neighbour's) is
>pointing.
>

Thats really quite close , assuming there are no big obstructions in
the way like hills I would have thought there should be plenty of
signal for all analogue channels.

Have you checked the connections and coax ? A quick check that the
loft aerial is giving a better signal than a set-top aerial might be
worthwhile.

It it was diy job by previous owner and the aerial isnt wide-band did
he buy the right one ?

Robert

Alan

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Jul 22, 2007, 11:04:15 AM7/22/07
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In message <MKHoi.625$Db6...@newsfe3-win.ntli.net>, Julian
<j...@supanet.com> wrote

>
>Thanks for your help. I'm thinking that I need to mount the aerial outside
>and use some decent cable. Cable won't be easy because most of it is buried
>beneath the plaster :-(

It may be easier to run a new cable outside of the house.

If the previous owner has run cable to all rooms did he also install a
distribution amplifier in the loft? It is not unknown for distribution
amplifiers to fail.

Julian

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Jul 22, 2007, 11:40:44 AM7/22/07
to

"Alan" <junk_...@amac.f2s.com> wrote in message
news:1yJuQqCv...@amac.f2s.com...

No, there's just a little 'Y' two into one affair in the loft. I've also
tried the telly up in the loft via an extension cord and connected direct to
the aerial to eliminate stuff.

I'm now 99% certain that the problem lies with the aerial location, so I'll
get it moved or replaced to outside, probably by professionals - there's too
much PFM with this signal stuff for my liking!

Julian.


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