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Astrolabe or inclinometer?



 
 
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  #21  
Old September 8th 16, 02:07 PM posted to uk.tech.digital-tv
Robin[_8_]
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Default Astrolabe or inclinometer?

On 08/09/2016 14:18, Java Jive wrote:
On Thu, 08 Sep 2016 11:13:08 +0000, Paul Ratcliffe wrote:

On Thu, 8 Sep 2016 10:25:33 +0000 (UTC), Java Jive

wrote:

since dishes have to be aligned to ~0.1 degrees,
probably ~0.05 degrees for a rotor, I wouldn't even begin to trust it.


What utter rubbish from Charley McFarley.
Don't think he lives in the real world...


What is your figure for the required accuracy then? I note that you don't
offer one.

I'm a numpty when it comes to satellite TV but once upon a time I
thought I understood how to work out the angular resolution of a
telescope (on the conventional basis from the Airy disk[1]). But having
had a shot at applying that to a domestic dish (say 0.6m) and Astra 2E
(say 10GHz) I end up with around 3 *degrees* which suggests 0.1 degree
accuracy would be otiose. Has my physics rotted even further than I knew?

[1] angular resolution [rad] = 1.22 x (wavelength)/(frequency)



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Robin
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  #22  
Old September 8th 16, 02:27 PM posted to uk.tech.digital-tv
Robin[_8_]
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Default Astrolabe or inclinometer?

On 08/09/2016 15:07, Robin wrote:


[1] angular resolution [rad] = 1.22 x (wavelength)/(frequency)


Buggerit.

angular resolution [rad] = 1.22 x (wavelength)/(DIAMETER)

(and preferably with wavelength and diameter in the same units)

--
Robin
reply-to address is (intended to be) valid
  #23  
Old September 8th 16, 02:56 PM posted to uk.tech.digital-tv
Paul Ratcliffe
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Default Astrolabe or inclinometer?

On Thu, 8 Sep 2016 13:18:21 +0000 (UTC), Java Jive
wrote:

since dishes have to be aligned to ~0.1 degrees,
probably ~0.05 degrees for a rotor, I wouldn't even begin to trust it.


What utter rubbish from Charley McFarley.
Don't think he lives in the real world...


What is your figure for the required accuracy then? I note that you don't
offer one.


What's the beam-width of your average little $ky dish and how
much does it move in the wind? That'll give you more of a clue.

At one point (not sure if this is still true) some of the satellites
were 0.3 degrees apart, so your 0.05 claim looks rather silly.
  #24  
Old September 8th 16, 04:47 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
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Default Astrolabe or inclinometer?

On Wednesday, 7 September 2016 23:20:59 UTC+1, Java Jive wrote:
On Wed, 07 Sep 2016 13:44:31 -0700, Andrew Rowland wrote:

Been to a couple of houses recently surrounded on all sides by tall
trees. One in particular was very keen to get Sky and we spent some time
looking for locations where a dish might be able to peer through a small
gap in the foliage. I used an inclinometer app on my phone, but found it
next to impossible to hold it steady at 23.1° while sighting along it to
see if we were looking at sky or forest canopy.
Does anyone know of a device that lets you look along or through it
while simultaneously being able to see the bubble or plumb line so you
know you are holding the thing level? Or has anyone found an different
solution to the problem? Bill said recently 'look SSE and slightly up'
but I need a bit more accuracy than that when things are tight! I'll
probably construct myself a gadget out of cardboard but I am not sure
the best way to go about it...


You can create an inclinometer using a protractor. If you really want to
be fancy, you can also tape it to a spirit level for the duration.


Or use a spirit level with one in like one I have (originally for getting the fall right on drains).

You could set a telescope up to look at the right spot.
  #25  
Old September 8th 16, 04:55 PM posted to uk.tech.digital-tv
Java Jive[_2_]
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Default Astrolabe or inclinometer?

On Thu, 08 Sep 2016 14:56:16 +0000, Paul Ratcliffe wrote:

On Thu, 8 Sep 2016 13:18:21 +0000 (UTC), Java Jive
wrote:

What's the beam-width of your average little $ky dish and how much does
it move in the wind? That'll give you more of a clue.

At one point (not sure if this is still true) some of the satellites
were 0.3 degrees apart, so your 0.05 claim looks rather silly.


It depends on whether we're just talking about aligning UK satellites at
Astra 28.2E or the wider world in general. I'm talking about making a
calculator app that will work worldwide. Although the average separation
between clusters is 2-3 degrees, there are a significant number of
neighbouring clusters separated by only 1 degree, and the smallest
separation is 0.7 degrees. Going on the principle that your calculator
should be an order of magnitude more accurate than the other errors of
alignment that will inevitably occur during installation, that means you
want to keep your calculator's errors to about 0.1 degrees. If you are
aligning a rotor, the margin for error is significantly smaller, so you
need another order of magnitude again, hence the 0.05 degrees.

That's the theory, but of course in practice that's difficult to achieve.
In particular, most calculators, including my own, use geometrical
calculations that assume the Earth is a sphere, which limits the accuracy
to about 0.3 degrees. To get it down to the 0.1 degrees that I'd like it
to have, I'd have to perform elliptical geometry, but that's a great deal
more complicated to implement, because it involves much more complicated
maths, including iteration over a process until an acceptable level of
accuracy is obtained.

The problem with the Satellite Director app mentioned up thread, and many,
many similar such methods, is that its creators are probably completely
ignorant of the sources of error in their app, and how significant these
errors are in relation to the accuracy required to align a dish to the
desired satellite cluster. Consequently, their level of error is likely
to exceed, quite possibly dwarf, the human installation errors that also
will inevitably occur, and thus there is a very real danger of its users
being directed to the wrong cluster, and their getting greatly confused on
not receiving the channels that they would be expecting to receive. Such
an app's apparent simplicity may be appealing initially, but if it can't
land you on the right cluster, then you'd do much better to use a more
reliable method that can.

--
Please reply to newsgroup
  #26  
Old September 8th 16, 06:09 PM posted to uk.tech.digital-tv
Andrew Rowland[_2_]
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Default Astrolabe or inclinometer?

On Thursday, 8 September 2016 10:13:27 UTC+1, Woody wrote:
Get the free Satellite Director. ...
Woody

This works great! Thanks for the recommendation. The app I was using is not half so good.
  #27  
Old September 8th 16, 06:20 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Default Astrolabe or inclinometer?

On 08/09/2016 12:28, Peter Duncanson wrote:

Would a sextant work?


We had a sextant in our parish but the bishop sacked him.

Bill

  #28  
Old September 8th 16, 06:22 PM posted to uk.tech.digital-tv
Andrew Rowland[_2_]
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Default Astrolabe or inclinometer?

Thank you all for your suggestions. A cardboard sextant would pretty much answer the need, but as the Satellite Director app does the trick and I'm happy with that.

I totally take on board what people say about trees moving and growing. However, I had a situation where I was being asked whether sat was possible by peering under the branches of some pretty big (and protected) trees, and wasn't able to give a definitive answer, so I didn't make much of a good impression. The householder didn't want to mount the dish at the entrance to the property and dig a trench or hang a catenary wire, and he wouldn't have it on the lawn or patio, so he didn't leave himself many options. But it wasn't really my problem: I left it to the Sky guys.
  #29  
Old September 8th 16, 06:41 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Default Astrolabe or inclinometer?

It bloody makes me laugh this does. We started off with somebody
wondering how he could figure out whether the tress were in the way of
the satellite signal. After a bit of ******** had been spouted I said
that the only foolproof way was to use a dish and a receiver. The basis
for this assertion was that I've been installing dishes since satellite
TV first started, and I've done thousands of installs. I've had more
than my fair share of awkward jobs partly because the local Sky
installers always fight shy of them. All this accumulated expertise
counts for nothing it seems. How much notice do you lot take? Sweet ****
all that's how much. The ******** continues to be spouted with talk of
spirit levels, telescopes, electron microscopes and borrowing the MRI
scanner from the local hospital. Deary deary me! Why not just accept the
word on somebody that knows and leave it at that?

Bill
  #30  
Old September 8th 16, 07:05 PM posted to uk.tech.digital-tv
Woody[_5_]
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Default Astrolabe or inclinometer?


"Bill Wright" wrote in message
...
It bloody makes me laugh this does. We started off with somebody
wondering how he could figure out whether the tress were in the way
of the satellite signal. After a bit of ******** had been spouted I
said that the only foolproof way was to use a dish and a receiver.
The basis for this assertion was that I've been installing dishes
since satellite TV first started, and I've done thousands of
installs. I've had more than my fair share of awkward jobs partly
because the local Sky installers always fight shy of them. All this
accumulated expertise counts for nothing it seems. How much notice
do you lot take? Sweet **** all that's how much. The ********
continues to be spouted with talk of spirit levels, telescopes,
electron microscopes and borrowing the MRI scanner from the local
hospital. Deary deary me! Why not just accept the word on somebody
that knows and leave it at that?



Come on Bill, that would be far too easy - and well you know it!


--
Woody

harrogate3 at ntlworld dot com


 




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