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In article , Bill Wright
scribeth thus

"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



You can nudge the main beam down a bit by adjusting the phasing, simpler
to do electrically than mechanically..

Sometimes;)...
--
Tony Sayer

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In article , Bill Wright
wrote:

"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?


No, you misinterpret what was happening. The standard cardioid has a built
in beam tilt when it leaves the factory. By tilting it back about 5
degrees the beam tilt becomes much less. When a low mast is in use and the
land is quite flat this was an economic way of solving a problem. Yes, I'm
sure a specially built cardioid (with zero beam tilt) could have achieved
the same result, but at a far higher cost.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

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"charles" wrote in message
...
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.

I guess that's the achilles heel of analogue TV.

Bill

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wrote in message ...
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.

Oh, that's on MB21. I took a picture of it. Wensleydale or Swaledale
somewhere.

Bill

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"tony sayer" wrote in message
...
In article , Bill Wright
scribeth thus
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



You can nudge the main beam down a bit by adjusting the phasing, simpler
to do electrically than mechanically..

'A bit' I can understand. But to go beyond the point where the transmission
is aimed to one side of the -3dB point of the main lobe seems perverse.

Bill

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"charles" wrote in message
...
In article , Bill Wright
wrote:

"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?


No, you misinterpret what was happening. The standard cardioid has a
built
in beam tilt when it leaves the factory. By tilting it back about 5
degrees the beam tilt becomes much less. When a low mast is in use and
the
land is quite flat this was an economic way of solving a problem. Yes,
I'm
sure a specially built cardioid (with zero beam tilt) could have achieved
the same result, but at a far higher cost.

I thought we were talking about crossed and bayed logs. We were, actually.
In the bit quoted above the cardiods were introduced after the phasing
discussion ended.

Bill

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"Bill Wright" wrote:

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?

It would be perverse in a receiving aerial because you'd lose signal
power. With a transmitting aerial, no power is lost as such -- it
increases the aerial's impedance.

--
Dave Farrance

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"Dave Farrance" wrote in message
...
"Bill Wright" wrote:

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?

It would be perverse in a receiving aerial because you'd lose signal
power. With a transmitting aerial, no power is lost as such -- it
increases the aerial's impedance.

Come again?

Bill

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

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

"Bill Wright" wrote:

"Dave Farrance" wrote in message
.. .
"Bill Wright" wrote:

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?

It would be perverse in a receiving aerial because you'd lose signal
power. With a transmitting aerial, no power is lost as such -- it
increases the aerial's impedance.

Come again?

Power has to go somewhere. If a receiving aerial has "poor
characteristics", this basically means that signal power that it should
be picking out of the air slips past it instead. But if a transmitting
aerial has been designed with what you might think by similarity to be
"poor characteristics", which gives it a higher impedance, you just turn
up the voltage feeding it (e.g. with a matching transformer) to get your
desired radiated power. i.e., the power going up the cable to the
transmitting aerial that's not lost as heat must be transmitted.

--
Dave Farrance