Technical info behind ku motor setup

[DruzeTito]

I finally took some time to look into the "technical" stuff of why we have to setup motors in a specific way. The setup is so simple and dumbed down that we never find out why things are done the way they are. Knowing the technical information behind it can save you hours of frustration of motor setup and arc tracking. http://www.geo-orbit.org is an awesome resource to use although most of the stuff highly leans toward c-band. I still have some unanswered questions and i will list them later.

Facts:

- An HH-motor (Horizon to Horizon) tracks satellites in the sky in an imaginary belt called the "Clarke Belt."

-Most television satellites on earth are 22,000 miles above the equator with varying distance between one and another. Since they are in an orderly fashion, the motor is designed to track them exactly based on what elevation you have set it to (also latitude setting) and if you have pointed it to your true south heading.

-When the motor moves, it moves azimuth, elevation, and skew all at once. This is why your lnb does not need adjusting but should be set to it's neutral position.

- When setting up the motor, there are three initial adjustments you must make: First is pointing your motor to your true south, then setting the elevation scale on the motor to your latitude (this is the elevation setting) and finally adjusting the declination angle on your dish.

- When fine tuning your dish for signal and quality, only adjust where the motor is pointing to (left.right) and the elevation setting on your dish (declination angle)

-The reason behind pointing your motor to true south is because this is used like a reference point for the motor. It is the position where your dish will aim at it's highest point on the belt.. this is called the "zenith".

- When adjusting the elevation on your dish in a motor setup, you are not really adjusting elevation (that has already been set on the motor) but you are adjusting the declination angle. To find out just what that means, read this very informative information here: http://www.geo-orbit.org/sizepgs/decchartp.html.

Looking at this image helps greatly to understand the meaning of these adjustments and the clarke belt.



As you can see, when we adjust the elevation of the dish (really the declination angle) we are kind of adjusting the "width" of how the motor will track the belt.

Please note that according to this image, we do not have to worry about elevation at all because it has been set on the motor scale to your latitude. What we have to worry about when peaking the signal is declination and north/south axis.

The importance of declination angle comes into play when the motor moves further east or west to lower elevations and higher skew angles. For example, when you have your motor pointing to the satellite closest to your true south, making declination adjustments to the dish have barely any effect to the signal/quality (given that you keep it in the reasonable range of your calculated value) because the basics have already been adjusted: elevation (on your motor) and azimuth (the pointing of your motor to true south).

Conversely, when the motor aims further east or west, if your declination angle setting is not right, the dish will aim into deep space somewhere and totally miss the satellite.

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Now I do have some interesting questions for people if they can answer. I find that, for my motor, SG2100, to "calculate" the declination setting of the dish, I must do (30 - declination angle of my latitude (found on the chart) ) .. my question is WHY 30?? Is this the average offset angle of a dish it is taking into account?

I ask about offset angle because, when I calculate it, not matter where you are, it goes from about 20 degrees to 29 degrees. Mine turns out about 25 degrees. I find that when my dish is at 25 degrees to it's scale it is a perfectly upright position at 0 degrees. The fortec 90 cm dish has about 24.62 degrees offset and the 80 cm is 22 degrees offset. This means that when either of them are pointed to this degree setting they are really aiming 0 degrees when measure with an angle finder.

So does declination angle set the dish to 0 degrees? Or does it calculate it to aim down about -4 degrees to not aim off into deep space? Because all declination angles are negative values on earth.

Or does this then all depend on how the motor is designed?

To calculate my declination angle, should I do (my dish's offset angle - my locations declination angle) to get a perfect setting?

This is what i am theorizing and thinking about. I haven't found any written info on this.

BTW... I hope new users find this info helpful.. if anyone finds any factual errors or bad wording in sentences please do tell!

[jackp]

Hello and thank you for asking the question.Good comment/you explaied correctly.Keep up the good work/so us newby can learn.I have been to that Geo site many time.Made 14 page copy.Now I have 2 drive motor(sg2100 and pm900)I am having a problem with my hotdish75 bracket.I remove the long bolt at the top/so the pm900 shaft can go in.Inside of the shaft,it don't line up.I have to used a smaller size bolt to go thru the shaft and bracket.Doing this made the elevation adjustment smaller/the shaft is hitting the boom arm top and bottom. Help

[DruzeTito]

it's quite difficult to visualize what your problem is because I have never seen or used a hot dish before. Mabybe sending pictures can help if you can.

[bobkat]

Damn Skippy !!!! Nice post. I'm making this baby a Sticky !!

kat

[DruzeTito]

thanks kat you are the greatest :-)

[DruzeTito]

I finally found the answers to my own questions after thinking about it for hours. =D>

The reason we have various motors having let's say 30-declination angle or X-declination angle is because 30 is the angle of the pole on the motor!!!

For the SG2100A's case, the pole on the motor is bent down precisely 30 degrees. Why is it bent? Well, if the pole was perfectly vertical then you wouldn't be able to set that slight negative declination angle because you cannot lower the dish less the around 5 degrees when it is on let's say a perfectly vertical pole!. So in a way, once the dish is on the motor, the dish's scale is off by -30 degrees!

So if you set the dish elevation on the scale to 30 when it's on the motor, then the real angle of the dish is 0, the perfect upright position. That is why in order to get that slight declination angle, you must do (0 - declination angle for your location) and it will turn out a negative number. Add 30 to that number and viola!! set your dish to that! Of course you know 30 - dec angle is much easier but I explain the opposite way so show why everything works out. It has nothing to do with the offset of the dish at all.

So in an example install with latitude of 28.0 N and 82.5 W , first let's take a look at some parameters for this location.

A real good site to calculate this stuff is www.satlex.de

Just input the satellite's longitude as your own longitude and you will get your area's declination angle and your highest elevation value!

- The declination angle for this location is -4.65
- The highest point, or the "zenith" of this location is 62 degrees, this does not include the declination angle. If we include the declination angle, it will be (62 - 4.65 = 57.35 ) This says that if there was a satellite on 82.5 W longitude that I needed to point to as a fixed dish, I would set the elevation on the dish's scale to 57.35. My elevation on a fixed dish would NEVER go higher than that because it is the zenith of my location or highest point.

So now, if I wanted to include a motor here is what the goal is:

The goal is to point the motor to my true south, adjust the motor's elevation bracket to my latitude, and finally adjust the declination angle on the dish to get the resultant pointing of the dish to be 57.35!

Here's how we get there: First we point to true south; Then I adjust the motor's bracket to my latitude to 28.0 N, on the other side of the scale I get 62 degrees! How does latitude translate into degrees? Here's how: 180-90-28= 62!! Dont ask me how i got this! It has something to do with the coordinate system.

Ok, so we have 62 deg, but we need a final value of 57.35 deg elevation.

So now we put the dish on. Since the motor's arm is bent down 30 degrees, we need to make the dish point to -4.65 for our declination. Add 30 degrees to -4.65 and you get 25.33. So set the dish to this value and we now finally have our 57.35 degrees elevation! Of course, if you take offset into account, the dish is pointing 24.62 degrees lower than the incoming signal at 57.35 degrees.. Assuming the dish offset is 24.62 degrees: (57.35 - 24.62 = 32.73) But the scale is adjusted to match the real incoming elevation.

I hope someone can understand this! :mozilla_smile:

[redman2]

Tito,

I read your "how to" post and I have some questions. I tried to install a sat. system: Winegard 76cm, Invacom LNB and GS120(SG2100) motor. My location: zip 92009 (USA/Calif - Lat 33.09 N/ Long 117.26 W) I used the declination table and got 5.38. Therefore , the dish angle should be 30-5.38 = 24.62 approx 25. The angle for the motor should be 33 (matches the lat.) Total = 25+33= 58. Here comes my problem: I cannot set the angle of the dish to 24. The lowest I can go is 30 as the motor mast hits one of the LNB installation screws. Maybe I didn't install the dish support right? And, even at those 30 deg. the mast of the motor is paralel with the LNB support bracket(at the back of the dish). Can't I make up the 58 deg using the motor's elevation bracket? Therefore, considering that the motor's pole is bent at 30 deg. I should set the motor elevation at 58-30=28 deg. Am I correct? Will this work?
Thanks in advance for your help!

[DruzeTito]

well I know the winegards are weird. I cannot imagine why anyone wouldnt make a offset ku dish go less than 30 degrees as there are plenty of satellites that need less than 30 degrees.

no i dont think you can set the motor elevation to compensate because the elevation must be set to your latitude or 57 degrees.

What the dish is doing is setting the declination to actually "hit" the satellites because they are relatively close to the earth, if no declination was set and the dish was set level with the motor's elevation it will miss the satellites and aim into deep space.

as i said, the SG2100's motor is bent down 30 degrees, because if it wasn't bent at all, it would be impossible to put the dish at a negative value to set the declination!

I'm not sure what other chances you got, but all i can think of now is maybe you should get a SMD312 motor, because it's arm is bent down even more: about 42.5 degrees i think. That just may cut it for your dish.

[redman2]

Thanks for such a quick answer! To be honest, I was hoping for a quick fix! Or, at least a motor kit available for this dish.Oh well... What I don't understand is how come this combination (Winegard 76 & SG2100/GS120 ) is such a popular package: there are many companies that sell it as a package (including the receiver also). By the way, what other sites do you you know that will show you how to install the dish? I am not sure I got the TRUE SOUTH correctly. This is how I did it: I aligned the North index line with the North magnetic needle and the 150 indication on my compass points to TRUE SOUTH. Is that correct? By the way, are the other calculations of mine (see previous message) correct? Thanks again!

[DruzeTito]

AH!! You live by San Diego! One of my favorite cities i've seen and someday i want to move there. You must be rich.. lol.

Well yes, most of your calculations are correct. Only don't add 25+33 to get 58. The declination setting of the dish is independent and in your case it conicidentally equals to the elevation setting of the motor.

It three simple steps: set the motor to your latitude, set your declination angle on dish to 25 and point the whole motor/dish by hand to 180-13= 167. Point it to 167 on your compass. However method you use, make sure it turns out like that.

Now as for your winegard not going under 30, there must be something wrong.. hmm. What is the lowest number that the dish's bracket says?

And you say "the motor mast hits one of the lnb installation screws" I am confused by this statement. The LNB is all the way in the front of the dish, how can it interfere?

[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]

Originally Posted by 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?

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.

Originally Posted by freeview

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]

Originally Posted by freeview

...
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.