How much sky does dish need to see?

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

wrote in message
...
I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are essentially
parallel. Fresnel effects are insignificant. So the dish needs a clear view
from every part of its surface to the satellite, and that's all.

See

http://www.wrightsaerials.tv/referen...ed-by-roof.pdf

Bill

On 3 Feb, 17:09, "Bill Wright" wrote:
wrote in message

...

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are essentially
parallel. Fresnel effects are insignificant. So the dish needs a clear view
from every part of its surface to the satellite, and that's all.


Thanks Bill, that make sense. I'll redo my angles on that basis.

wrote in message
...
On 3 Feb, 17:09, "Bill Wright" wrote:
wrote in message

...

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it
needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are
essentially
parallel. Fresnel effects are insignificant. So the dish needs a
clear view
from every part of its surface to the satellite, and that's all.


Thanks Bill, that make sense. I'll redo my angles on that basis.




If there are any incursion problems you can use a bigger dish which has
a narrower beamwidth.



--
Woody

harrogate three at ntlworld dot com

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are
essentially
parallel. Fresnel effects are insignificant. So the dish needs a clear
view
from every part of its surface to the satellite, and that's all.


Thanks Bill, that make sense. I'll redo my angles on that basis.

I imagine the satellite as an intense point of light, then I ask
myself if anything will cast a shadow on the dish.

--
Graham.

%Profound_observation%

"Woody" wrote in message
...
wrote in message
...
On 3 Feb, 17:09, "Bill Wright" wrote:
wrote in message

...

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are
essentially
parallel. Fresnel effects are insignificant. So the dish needs a clear
view
from every part of its surface to the satellite, and that's all.


Thanks Bill, that make sense. I'll redo my angles on that basis.




If there are any incursion problems you can use a bigger dish which has a
narrower beamwidth.

It might improve the signal because the larger surface area means the
obscured proportion is relatively small. I'm not convinced it is directly
connected to the tighter focus per se, the dish will still be obscured,
but there will be more dish.

--
Graham.

%Profound_observation%

"Woody" wrote in message
...
wrote in message
...

If there are any incursion problems you can use a bigger dish which has a
narrower beamwidth.

That could help if the incursion was the source of radiated interference,
but not if it was merely a screen from the 'bird'.

Bill

"Graham." wrote in message
...
I imagine the satellite as an intense point of light, then I ask
myself if anything will cast a shadow on the dish.

I think that approximation is more than adequate for this purpose. This
discussion puts me in mind of an incident in 2002. I might have told the
tale here before; if so please forgive an old man his aberations.

The development was off Park Grange Rd, Sheffield. The head-end and thus the
dish were to be on a new build block of 5 or 6 floors. The architect said
that the dish had to be out of sight, so that meant it had to go on the back
wall of the lift motor room, which fortuitously faced south-east. From the
ground though, it was obvious that the line-of-sight might be obstructed by
a tower block (I just looked on Google Local and Multimap and you can see
the tower, but not the new development, so both maps must be well out of
date.) The problem was that the developer would only pay for one visit by
the £500 per trip machine that was the only was we could get onto the roof.
We'd suggested a maintenance hatch but they'd said no.) To complicate
matters the tower should have been demolished by then but the council had
postponed the event. If only our job could have waited a few weeks there
wouldn't have been a problem, but again the developer said no. So we knew we
might have to fix the dish and then someone would have to find the money for
a second day with the machine just to align it. I found the place on the
ground where the lift motor room obstructed the view of the satellite, and
tried to figure out if the tower would in fact be in the way, but the result
was, maybe it will, maybe it won't. In the end the machine came and we were
hoisted aloft. The edge of the RF shadow of the tower block on the back of
the lift motor room fell about a metre from the corner, so we had a metre to
play with. I squeezed the dish on there. The shadow had a razor-sharp edge,
as far as I could tell with just an 85cm dish as an optical instrument!
Certainly it was possible to put the dish in a place where a hand over the
left half did nothing, whilst a hand over the right half reduced the signal.

Bill

On Tue, 3 Feb 2009 09:03:42 -0800 (PST), wrote:

I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

If you want to be certain that the dish has a clear path, check that
its view of the sun is unobstructed on 1st March at 10.08 GMT. At that
time it will be precisely behind the Astra 2 satellites.
(It will be cloudy that day, of course!)

As long as there are no metallic surfaces that might add a reflected
component I suppose. Mind you I only saw this on an old Analogue pace system
way back when...

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Bill Wright" wrote in message
...

wrote in message
...
I'm looking to relocate my Sky mini-dish however the new location
means that the angles are very tight. For Sky, I'm assuming it needs
to point to Astra 2A which has an elevation of 24.5 degrees and
azimuth of 148 from here in South London.

There is a roof ridge about 6 metres in front at an elevation of 23
degrees. As to the azimuth there is a margin of 2 degrees to spare
before an other obstacle gets in the way.

Basically the queston is whether this is too tight. If so, just how
wide an angle does a dish need?

The lines drawn from the edges of the dish to the satellite are
essentially parallel. Fresnel effects are insignificant. So the dish needs
a clear view from every part of its surface to the satellite, and that's
all.

See

http://www.wrightsaerials.tv/referen...ed-by-roof.pdf

Bill