What time of day should equate to my Dish Position

muchos04 · 18-08-2010 08:15AM #1

Hello,

Can anyone tell me at what time of day i need to have my satellite dish pointing in the sky for Astra28.2E?

Currently it is pointing at the sky at 12 o' clock in the afternoon. I get all the UK FTA channels fine except Russia Today and sometimes France 24 are blotchy.

Regards
muchos04

almighty1 · 18-08-2010 08:42AM

You mean pointing at the sun? Generally its around 11-12 but its not an exact science. You'd be better to get a loan of a satellite meter and align it properly.

Apogee · 18-08-2010 08:47AM

The position of the sun is only ever a rough guide to aligning a dish. The fact that you are already receiving the channels means the sun is of no further use to you.

You should open up the programming menu in the receiver, and watching the signal quality meter, very slowly move the dish up/down, and then east/west to see if it improves the reading.

Also make sure the skew (twist) on the LNB is right - see point 7.
http://sites.google.com/site/freetoairinfo/home/how-to-align-a-satellite

Sam Russell · 18-08-2010 09:25AM

You are looking for 28.2 deg east of south.

28.2/360*24*60 minutes before midday. 112.8 mins.

Midday is 1 pm summer time. So sun is above the satellite at 11.07 am.

Or use this.

http://www.satcomresources.com/Satcom-Dish-Pointer-with-Google-Maps

watty · 18-08-2010 09:38AM

We are somewhat west. Here Midday is more like 1:20. It would be 1pm at Greenwich London.

Sam Russell · 18-08-2010 11:42AM

watty wrote: »

We are somewhat west. Here Midday is more like 1:20. It would be 1pm at Greenwich London.

You are right of course, but I did suggest that midday was the criterion, not noon.:)

watty · 18-08-2010 12:41PM

Sometimes I'm wrrr

Sometimes I'm wrong

muchos04 · 18-08-2010 01:22PM

Cheers for all the info guys,

When i look at the receiver and it is on Astra 23.5E, signal and quality are at constant levels of around 80%. When i flick to Astra 28.2E the signal and quality stay at 80% for around 30 seconds then drop to about 16% and then back up again. I can get all channels fine but just one or two such as AbuDhabi TV, France 24 and sometimes Russia today are blocky?

Any ideas?

regards

Tony · 18-08-2010 01:37PM

Ok , ignore the reading on 23.5 , with one lnb its impossible to receive both positions it just happens that there are similar transponders. Check your dish alignhment and lnb skew, heres a video that you may find helpful, just F forward to the alignment part.

https://www.youtube.com/watch?v=dl-rawdjA0Y

muchos04 · 18-08-2010 02:10PM

Thanks very much Tony,

I'll take a look!

Regards

sesswhat · 18-08-2010 02:12PM

Sam Russell wrote: »

You are looking for 28.2 deg east of south.

28.2/360*24*60 minutes before midday. 112.8 mins.

Midday is 1 pm summer time. So sun is above the satellite at 11.07 am.

The calculations above only apply if you are at the North Pole.

If you take a central location in Ireland, say Athlone, the azimuth to the satellite is 137.7 deg, or 42.3 deg east of south.

Today, the sun shared this angle at just after 11.34.

I realise this is all of little value to the OP who would be much better off watching Tony's video

Tony · 18-08-2010 02:22PM

sesswhat wrote: »

I realise this is all of little value to the OP who would be much better off watching Tony's video

good one

Sam Russell · 18-08-2010 04:02PM

sesswhat wrote: »

The calculations above only apply if you are at the North Pole.

If you take a central location in Ireland, say Athlone, the azimuth to the satellite is 137.7 deg, or 42.3 deg east of south.

Today, the sun shared this angle at just after 11.34.

I realise this is all of little value to the OP who would be much better off watching Tony's video

The north pole is not a good point to try to align a satellite dish as there is no east or west, only south.:)

All the OP wanted was an indication. The calculation tells the time that the sun is above the satelite, not in line with it. The sun is a loooong way above it and you would have to solve the triangle formed by the sun, satellite and the OP. If he looks out at 11 am or 11:34 am, I think he will have the same problems aligning his dish. He wont latch onto 19E. But I did say dishpointer was more use, using local landmarks to point in the right direction.

Obviously the further west he is the greater the error.

Apogee · 18-08-2010 04:45PM

Sam Russell wrote: »

You are looking for 28.2 deg east of south.

28.2/360*24*60 minutes before midday. 112.8 mins.

If I'm not mistaken, you're assuming that the OP is living on the Greenwich Meridian, as otherwise Astra 2 is not "28.2 deg east of south".

The calculated sunpass time for Dublin is 11.33am (10.33am UTC).
http://www.satellite-calculations.com/Satellite/lookangles.htm

All of this is academic, as he's already aligned to Astra 2, but his alignment is not optimised.

muchos04 · 18-08-2010 06:25PM

Hi guys,

Yes i am in west in Galway.

Regards

sesswhat · 18-08-2010 07:05PM

Apogee wrote: »

All of this is academic

We all agree on that so it's just a bit of geekery at this stage

Apogee wrote: »

If I'm not mistaken, you're assuming that the OP is living on the Greenwich Meridian, as otherwise Astra 2 is not "28.2 deg east of south".

Even on the Greenwich Meridian, as you move away from the North Pole, the angle will be greater until you reach the equator, where it will be 90 degrees.

Apogee · 18-08-2010 07:21PM

sesswhat wrote: »

Even on the Greenwich Meridian, as you move away from the North Pole, the angle will be greater until you reach the equator, where it will be 90 degrees.

The angle to what?

sesswhat · 18-08-2010 07:27PM

Apogee wrote: »

The angle to what?

The angle formed by the Greenwich Meridian, looking south, and a line along the surface in the direction of the satellite.

Only at the North Pole is this angle 28.2 dgrees.

Tony · 18-08-2010 07:33PM

sesswhat wrote: »

Only at the North Pole is this angle 28.2 dgrees.

Which is really hard to find as a compass does not work at the North pole

( before some else says it, the satellite is below the horizon anyway )

sesswhat · 18-08-2010 07:48PM

Tony wrote: »

Which is really hard to find as a compass does not work at the North pole

( before some else says it, the satellite is below the horizon anyway )

Compasses are old hat. I got one of them fancy satnavs fitted in me nuclear sub at halfords.

And I have a very tall periscope to put the dish on

Tony · 18-08-2010 08:17PM

sesswhat wrote: »

And I have a very tall periscope to put the dish on

better not look through the persicope at 11.30 though, you'll be blinded:)

Sam Russell · 18-08-2010 09:06PM

sesswhat wrote: »

Only at the North Pole is this angle 28.2 dgrees.

It is only at the equator, at 28.2 deg east, the satelite is overhead, with the sun directly over head, as long as it is an equinox.

At the north pole, there is only south, no east no west. Just south.

Tony · 18-08-2010 10:04PM

Boy this is geeky:). At the equator its neither south nor north its overhead so azimuth is pretty irrrlevant , however if you go just a few miles north of the equator at the greenwich line its will be way over 28 degrees east of south, more like 45 east as stated earlier. At the north pole its still 28.2 east of the Greenwhich meridian , obviously everywhere from the north pole is south.

Apogee · 18-08-2010 11:19PM

sesswhat wrote: »

Even on the Greenwich Meridian, as you move away from the North Pole, the angle will be greater until you reach the equator, where it will be 90 degrees.

I can't see where you're getting 90 deg from unless you're on about elevation?

The azimuthal bearing is measured relative to the centre of the earth's core. There are small corrections that are taken into account depending on your location on the surface of the planet e.g. a 3 degree orbital spacing isn't really a 3 degree spacing depending on the location of the observer.

I dig out the reference and post a scan of it.

almighty1 · 19-08-2010 07:56AM

Moved to Astronomy

sesswhat · 19-08-2010 09:07AM

Apogee wrote: »

I can't see where you're getting 90 deg from unless you're on about elevation?

The azimuthal bearing is measured relative to the centre of the earth's core. There are small corrections that are taken into account depending on your location on the surface of the planet e.g. a 3 degree orbital spacing isn't really a 3 degree spacing depending on the location of the observer.

I dig out the reference and post a scan of it.

It's nothing to do with elevation.

At the point where the Greenwich meridian crosses the equator, the satellite at 28.2 E, along with many others, is due east along the equator, or 90 degrees east of south.

Sam, the method you used originally could be perfect if the sun was always over the equator.

You worked out how long it would take for the sun's position to change from a longitude of 28.2 degrees (same as the satellite) to a longitude of 0 degrees (due south, or midday, at Greenwich).

28.2/360*24*60 minutes before midday. 112.8 mins.

Because midday at greenwich is 1pm summer time, the sun was at the same longitude as the satellite at 11.07.

However, as you point out, it is only during an equinox that the sun is over the equator all day. At other times, being at the same longitude does not mean it will appear to be directly over the satellite (unless you are looking at them from the Poles).

In summer the sun is over a point further north and so at 11.07 it is a bit to the left of the satellite as we look at it. Yesterday it took until 11.34 to 'catch up'.

Sam Russell · 19-08-2010 10:26AM

sesswhat wrote: »

It's nothing to do with elevation.

At the point where the Greenwich meridian crosses the equator, the satellite at 28.2 E, along with many others, is due east along the equator, or 90 degrees east of south.

Sam, the method you used originally could be perfect if the sun was always over the equator.

You worked out how long it would take for the sun's position to change from a longitude of 28.2 degrees (same as the satellite) to a longitude of 0 degrees (due south, or midday, at Greenwich).

Because midday at greenwich is 1pm summer time, the sun was at the same longitude as the satellite at 11.07.

However, as you point out, it is only during an equinox that the sun is over the equator all day. At other times, being at the same longitude does not mean it will appear to be directly over the satellite (unless you are looking at them from the Poles).

In summer the sun is over a point further north and so at 11.07 it is a bit to the left of the satellite as we look at it. Yesterday it took until 11.34 to 'catch up'.

Because of all that, it is only a guide to the installer to point in roughly the right direction, or to assess where to bolt the dish. The dishpointer site will give useful landmarks to use and is much more use when trying to find the right satellite. The signal meter or a satfinder beeper will get a rough elevation, and azimuth, and final tweeking using a receiver with good signal strength indication to set the final positions of elevation azimuth and skew.

Three dimension trignometry is hard enough at Leaving Cert, and that was a long time ago.

Apogee · 23-08-2010 10:05PM

sesswhat wrote: »

It's nothing to do with elevation.

At the point where the Greenwich meridian crosses the equator, the satellite at 28.2 E, along with many others, is due east along the equator, or 90 degrees east of south.

I see what you mean. I thought initially you were on about setting elevation for a polarmount on the equator.

The best definition I can cobble together is a planar angle of 28.2 degrees east of the plane which passes from the centre of the earth through the Greenwich meridian.

sesswhat · 24-08-2010 09:15AM

Apogee wrote: »

I see what you mean. I thought initially you were on about setting elevation for a polarmount on the equator.

The best definition I can cobble together is a planar angle of 28.2 degrees east of the plane which passes from the centre of the earth through the Greenwich meridian.

Yes, elevation adds its own complications. For the purposes of the OP's problem we can assume the satellite is sitting on the ground at the equator, while the sun is a spot rolling along the surface.

Sam Russell · 24-08-2010 10:29AM

Well, presumably what the OP wants is to know at what time is the sun behind the satelite, so the dish points at it. That is a lot more complicated to calculate, or very simple. Look at another dish that is correctly orientated, and see at what time the LNB casts a shadow directly onto the dish.

Simples.

watty · 24-08-2010 05:19PM

Download the windows software here:
http://www.smw.se/FreeSoftware.htm

If you enter a latitude and longitude and satellite postion it will calculate the elevation and azimuth. You can experiment with equator and poles.

also see http://www.techtir.ie/howto/sat-position-from-sun

What time of day should equate to my Dish Position

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