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In article , charles
scribeth thus
In article ,
wrote:
On 1 Feb,
charles wrote:

In article ,
Ian Jackson wrote:

If I am (say) 20 miles from a main transmitter, and there is no limit
on the height to which I can raise my TV aerial, how high would it
have to be before the signal strength began to fall (assuming
lossless coax)? And, if the coax was (say) CT100, again, how high?


It would depend on the height of the mast. You do the trigonometry.
Assume a beam tilt of 6 degrees.

3 degrees would be an exceptionally large beam tilt for a main station.
1-2 deg would be the norm.

I was probably thinking of relays.


Well FWIW as a lot of these use logs, I don't see them with down tilt if
at all?..
--
Tony Sayer

BBC/ITV Freesat, another tiny drop of info...
 

In article ,
tony sayer wrote:
In article , charles
scribeth thus
In article ,
wrote:
On 1 Feb,
charles wrote:

In article ,
Ian Jackson wrote:

If I am (say) 20 miles from a main transmitter, and there is no
limit on the height to which I can raise my TV aerial, how high
would it have to be before the signal strength began to fall
(assuming lossless coax)? And, if the coax was (say) CT100, again,
how high?


It would depend on the height of the mast. You do the trigonometry.
Assume a beam tilt of 6 degrees.

3 degrees would be an exceptionally large beam tilt for a main station.
1-2 deg would be the norm.

I was probably thinking of relays.


Well FWIW as a lot of these use logs, I don't see them with down tilt if
at all?..

any tilt is very rarely mechanical. It's done by using suitable lengths of
feeder. The other main relay aerial is a simple cardioid with 4 dipoles.
These are internally phased. One relay on South Uist has a mechanical
'lean back' to counteract the built-in beam tilt.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

BBC/ITV Freesat, another tiny drop of info...
 

In article ,
wrote:
On 2 Feb,
charles wrote:

In article ,
wrote:
On 1 Feb,
charles wrote:
It would depend on the height of the mast. You do the trigonometry.
Assume a beam tilt of 6 degrees.

3 degrees would be an exceptionally large beam tilt for a main
station. 1-2 deg would be the norm.

I was probably thinking of relays.

Yes, it is in the range of relays. Up to about 10deg. There's one that
looks odd, in that its beam tilt is about 2deg, and the panel was
designed to be somewhat higher, so the aerial is tilted back to reduce
it. We had lots of complaints about a faulty aerial as a result. Up one
of the Dales I think.

That's probably why on S Uist a back "supporting" stay was fitted to look
'right'.


An then there were at least two that were installed upside down, until the
poor reception became apparent.

One I met twice, initially when it was installed at Kilmacolm, but I didn't
know much about antenna then, so didn't recognise the fault and much later
when it was fitted (refurbished) at Kenmore. I understand that it was
actually assembled upside down inside the panel.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

BBC/ITV Freesat, another tiny drop of info...
 

In article ,
wrote:
On 2 Feb,
charles wrote:

In article ,
wrote:

Yes, it is in the range of relays. Up to about 10deg. There's one
that looks odd, in that its beam tilt is about 2deg, and the panel
was designed to be somewhat higher, so the aerial is tilted back to
reduce it. We had lots of complaints about a faulty aerial as a
result. Up one of the Dales I think.

That's probably why on S Uist a back "supporting" stay was fitted to
look 'right'.

More likely the weather up there.


no, cos it didn't actually touch the cardioid.



An then there were at least two that were installed upside down, until
the poor reception became apparent.

One I met twice, initially when it was installed at Kilmacolm, but I
didn't know much about antenna then, so didn't recognise the fault and
much later when it was fitted (refurbished) at Kenmore. I understand
that it was actually assembled upside down inside the panel.

Kilmacolm or thereabouts was one, SW Scotland.

But the Kilmacolm ones "escaped" and went on to Kenmore. And the site is
central Scotland. So perhaps there were three ;-(


The other was Seaham.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

BBC/ITV Freesat, another tiny drop of info...
 

In article , charles
scribeth thus
In article ,
tony sayer wrote:
In article , charles
scribeth thus
In article ,
wrote:
On 1 Feb,
charles wrote:

In article ,
Ian Jackson wrote:

If I am (say) 20 miles from a main transmitter, and there is no
limit on the height to which I can raise my TV aerial, how high
would it have to be before the signal strength began to fall
(assuming lossless coax)? And, if the coax was (say) CT100, again,
how high?


It would depend on the height of the mast. You do the trigonometry.
Assume a beam tilt of 6 degrees.

3 degrees would be an exceptionally large beam tilt for a main station.
1-2 deg would be the norm.

I was probably thinking of relays.


Well FWIW as a lot of these use logs, I don't see them with down tilt if
at all?..

any tilt is very rarely mechanical. It's done by using suitable lengths of
feeder. The other main relay aerial is a simple cardioid with 4 dipoles.
These are internally phased. One relay on South Uist has a mechanical
'lean back' to counteract the built-in beam tilt.


Yes understand that, but it doesn't seem to be applied and I rather
suspect its not needed anyway!...
--
Tony Sayer

BBC/ITV Freesat, another tiny drop of info...
 

In article ,
tony sayer wrote:

Yes understand that, but it doesn't seem to be applied and I rather
suspect its not needed anyway!...

The main reason for beam tilt is to stop the signal going too far out of
area and causing cci. With around 1200 sites each channel is, as you must
realise, used many times over.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

BBC/ITV Freesat, another tiny drop of info...
 

However, fairness compels me to volunteer that yesterday's edition of
'The Natural World' entitled 'White Falcon, White Wolf ' was much,
much better than most of the others in the current series have been.

Slight question about the framing of some gyr falcon aerial shots, in
that they seem to go out of frame rather too much, but I guess
following an animal that's free to change direction at speed in 3
dimensions is probably just about the most difficult thing a wildlife
cameraman ever has to track.

So I'll just say, darned good programme.

On Thu, 31 Jan 2008 16:35:20 +0000, Java Jive wrote:

Formerly, just about my favourite type of programme was Natural
History/Wildlife documentaries. I was transfixed by all the
Attenborough series, up to and including Planet Earth, by the time of
which fortunately I had FreeSat.
....
Add to that the modern style of showing us more of the scientists
researching the animals, or even less justifiably the cameramen, than
the actual wildlife, an occasional choice of irritating
presenters/commentators such as Titchmarsh or Sean Pertwee, he of the
voice from a horror movie, and these days I barely bother to even
record natural history/wildlife programs on a time-shift basis, let
alone with a view to keeping any recording more permanently.

BBC/ITV Freesat, another tiny drop of info...
 

In article , charles
scribeth thus
In article ,
tony sayer wrote:

Yes understand that, but it doesn't seem to be applied and I rather
suspect its not needed anyway!...

The main reason for beam tilt is to stop the signal going too far out of
area and causing cci. With around 1200 sites each channel is, as you must
realise, used many times over.


Quite. But thats very understandable on a 500-1000 foot main site but
some 25 ish metre low power relays perhaps not?..

Now what did they class those 1 kW ones now?..
--
Tony Sayer

BBC/ITV Freesat, another tiny drop of info...
 

In article ,
tony sayer wrote:
In article , charles
scribeth thus
In article ,
tony sayer wrote:

Yes understand that, but it doesn't seem to be applied and I rather
suspect its not needed anyway!...

The main reason for beam tilt is to stop the signal going too far out of
area and causing cci. With around 1200 sites each channel is, as you must
realise, used many times over.


Quite. But thats very understandable on a 500-1000 foot main site but
some 25 ish metre low power relays perhaps not?..

actually, yes. When a toy relay opened in N Wales, some viewers to a relay
near Rochdale started getting cci. I can't remember the site names - it
was about 20 years ago. you only need the interfering source to be 60dB
down to start seeing cci.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

BBC/ITV Freesat, another tiny drop of info...
 

"charles" wrote in message
...
any tilt is very rarely mechanical. It's done by using suitable lengths
of
feeder. The other main relay aerial is a simple cardioid with 4 dipoles.
These are internally phased. One relay on South Uist has a mechanical
'lean back' to counteract the built-in beam tilt.

So what you're saying is that the aerials are deliberately pointing in the
'wrong' direction and then the phasing is adjusted to give maximum radiation
in an off-axis direction. Seems a bit daft. Whay not simply point them in
the right direction and drive them in phase? What's the point in using
directional aerials if they are going to be driven in a way which competes
with the aerials' own characteristics?

Bill