Technical info behind ku motor setup

[DruzeTito]

actually here.. i found some good info on this winegard 76cm dish. Apparently this is a "special" dish that is a pain.. but according to this article: http://www.dvbresource.com/dishes/wi...gard_76_1.html ... it says that the lowest possible elevation is 20.5 degrees for the dish. If this is the case you dont have much to worry about. Click the link and keep on clicking next to read on and you'll see what im saying.

[Reinhold]

Hi,
After reading all the info you put on the forum,Ithink I have a better understanding of whats going on.It should help me greatly.I have one question though:after adjusting for the southern satellite perfectly won't the setting be thrown off when you make simular adjustments for the most east and the most west?

[sagirma]

Wow, This is an awsome thread, can get too deep for begginers, but really explains the whole picture clearly.

[born_a_reb]

hello to the group!

an easy way to find true north... and all you need is a newspaper!

1. buy "todays" newspaper...
2. look for the section that lists todays 'sunrise' and sunset' times
3. convert the sunset time to '24 hour time'
4. subtract the sunrise 'time' from the sunset 'time'
(make sure and get the minutes correct!)
5. divide the result by 2
6. add this number to the 'sunrise' time (as found in the newspaper)
7. the total will be what is known as 'local noon'

at local noon... all shadows point true north...(in the northen hemisphere)
lay a stick on the ground in back of your satellite pole....align it with the shadow....the stick will point true north and south....

is this easy enough?

[rainman]

or you can check this site. http://www.srrb.noaa.gov/highlights/...e/sunrise.html

[Reinhold]

Or you could alighn a stick to your true south setting using a compass,the plum down from your LNB with a plumbob for a correct true south setting.
Reinhold.

[freeview]

Hi, I am trying to install a FC90U with Stab HH90 at location [45.52N, 122.92W]. I have set my motor angle to the latitude 45.5 and the dish elevation angle to 45-6.83=38.17 Degrees (HH90 Shaft angle - declination).

Problem statement: The resulatant elevation angle of 38.17 does not match the elevation angle computed for a fixed dish mount using numerous calculators on the web.

For computation purpose let's suppose there is a satellite due south on your longitude -- in my case 122.92W. The calculator indicates that the elevation angle at this location should be 37.65 degrees. As you can see there is a discrepency of 38.17-37.65=0.52 Degrees; yes it is a small delta and may be ignored for all practical purposes.

Questions
1) Is the difference in elevation due to the setup procedure outlined in this thread?
2) Should the degree of elevation for fixed mount given by the dish manufacturer be taken into account as Stab HH90 procedure call for (http://www.stab-italia.com/eng-hh90.pdf) ? If so what is it for a Fortecstar FC90U?
3) Should the satellite elevation be taken into account when setting the angle and use this as offset factor from the latitude location to make up for the 0.5 degree difference?

[wejones]

Hi, I am trying to install a FC90U with Stab HH90 at location [45.52N, 122.92W]. I have set my motor angle to the latitude 45.5 and the dish elevation angle to 45-6.83=38.17 Degrees (HH90 Shaft angle - declination).
Problem statement: The resulatant elevation angle of 38.17 does not match the elevation angle computed for a fixed dish mount using numerous calculators on the web.

For computation purpose let's suppose there is a satellite due south on your longitude -- in my case 122.92W. The calculator indicates that the elevation angle at this location should be 37.65 degrees. As you can see there is a discrepency of 38.17-37.65=0.52 Degrees; yes it is a small delta and may be ignored for all practical purposes.

Questions
1) Is the difference in elevation due to the setup procedure outlined in this thread?

I think your problem here is that 45.5 is NOT your motor elevation. Your motor elevation is actually 90 MINUS your latitude. Ie 90-45.5=44.5 . Your motor has a latitude scale which is the opposite of an elevation scale.
So in fact, the actual angle that your dish is looking at when aimed south, is 44.5-6.83= 37.67, which is basically the same as the 37.65 number you found, considering the significant figures.

3) Should the satellite elevation be taken into account when setting the angle and use this as offset factor from the latitude location to make up for the 0.5 degree difference?

As you see above, there is not .5 degree difference. As I have posted several times, whenever I see someone who has a latitude near 45, the odds become very great that there will be confusion between elevation and latitude.
That being said, however, if you go to the geo-orbit web page mentioned at the start of this thread, you will see it recommended that you don't use a declination of 6.83 (which I think is the declination for 45 deg, not 45.5 BTW), but instead to use a declination of approximately 6.18 instead, and make up the difference by using a latitude number which is about .65 degrees higher. The reason for this is that the declination of sats to the east or west are lower (ie 6.18) so if you use that declination you will be OK to the east/west, and the decrease in your motor elevation will not affect the aim east/west (see your graphs for too much/little motor elevation, ie they still hit sats at the extremes.). If you do this, you will be tracking everywhere along the arc. If you use the 6.83 number, you will be off by .6 degrees at your extremes.

BTW, I don't agree with couple of the diagrams in the first post in this thread, but for the most part they are useful.

[freeview]

I see the error in the calculation as pointed out by wejones; The motor elevation should be 90-latitude. I searched the web to find out a clear procedure and explanation for this discrepency and stumbled upon the chart which has the modified latitude. http://www.geo-orbit.org/sizepgs/decchartp.html

Another thing that I spent some time thinking about is the "degree of elevation for fixed mount given by the dish manufacturer". Actually, I spent more time trying to contact the manufacturer for this data. Luckily their help is not needed in this equation as the offset is already built into the angle readout scale of the dish mount hardware -- so no need to contact the dish manufacturer for this data, as some motor manuals may suggest!

I appreciate your clarification wejones!

Thanks

[wejones]

...
Another thing that I spent some time thinking about is the "degree of elevation for fixed mount given by the dish manufacturer". Actually, I spent more time trying to contact the manufacturer for this data. Luckily their help is not needed in this equation as the offset is already built into the angle readout scale of the dish mount hardware -- so no need to contact the dish manufacturer for this data, as some motor manuals may suggest!
....

However, as was mentioned in some previous messages, the "readout scale" on the dish mount hardware, is notoriously innaccurate. I'm convinced that part of the reason is that although a mount needs to be specific to a dish since different dishes have different offset angles, sometimes the mounts on these dishes are generic or intended for another dish, so they can be off considerably. Some people here have reported that the angles are off by as much as 5 degrees. A while back, I posted the offset angles of several dishes at:

http://www.sadoun.net/forums/install...sues-data.html

Even the different sized Fortec dishes here have different offset angles, yet are often sold with either a generic mount or one for another dish. I recently got a 90CM dish, which came with hardware intended for an 80CM dish. I did some experimentation, and found the dish elevation scale to be slightly off, but actually pretty close compared to the 5 deg error that some reported.

http://www.sadoun.net/forums/install...ervations.html

I also noticed that the lnbf holder on my dish was not quite in the right place, which affects the apparent offset angle of the dish, and makes the scale wrong. So there are several reasons why the scale on these dishes can be in error. This scale should only be used as a starting point for finding the sats. The scale on the motors, however, is pretty accurate.