STAB: Calculating degrees of dish elevation angle?

[Sadoun]

Hi Guys

We just updated the "Motorized dish Elevation Angle" page slightly. I know a lot of you use this page. Here it is: http://www.sadoun.com/Sat/Installati...ion-Angles.htm

:mozilla_cool:

[videobruce]

If there is a elevation adjustment on the antenna, why is there one on the motor?

[Admin]

Of course. That is what that calculator is for.

[videobruce]

??? #-o

[rray32539]

Originally Posted by videobruce

If there is a elevation adjustment on the antenna, why is there one on the motor?

The elevation setting on the motor should equal the latitude of your location. If you are at 30 degrees north latitude, set your motor to 30 degrees.

[ahoss2000]

I think Sadoun web calculations for HH90 is off slightly. According to STA B, the dish angle = Fixed dish angle - (45 - Lat), for 32714 zip, =52-(45-28)=35 . Sadoun web calls for 40.

On my M1 system, 35 worked, 40 does not.

[wejones]

Originally Posted by ahoss2000

I think Sadoun web calculations for HH90 is off slightly. According to STA B, the dish angle = Fixed dish angle - (45 - Lat), for 32714 zip, =52-(45-28)=35 . Sadoun web calls for 40.

On my M1 system, 35 worked, 40 does not.

For ANY motor, the dish elevation should be set to:

MSOA - declination

where MSOA=motor shaft offset angle. For the HH90, the bend in the motor shaft is 45 deg . Therefore, the dish angle should be :

45- declination.

Now, you have 2 choices for declination some calculators use the declination of your south satellite, which is a poor approximation. For your latitude of 28, your south declination is 4.7 deg, so the dish elevation should be 40.3 . The better choice for declination (assuming that you have added about 0.6 to the latitude setting on your motor latitude scale) would be the declination of a western or eastern sat, which would be about 4.1 deg for your latitude. That would give you a dish elevation of 40.9 deg.
If your system is giving you better results at 35 deg, then something else is wrong with your system, ie either (1) the dish elevation scale is wrong, (2) the lnbf arm is bent, (3) you have the wrong setting on the motor elevation, (4) the dish elevation bracket isn't assembled properly, (5) etc.

[wejones]

Originally Posted by ahoss2000

..... According to STA B, the dish angle = Fixed dish angle - (45 - Lat), for 32714 zip, =52-(45-28)=35 . Sadoun web calls for 40.
....

BTW, I forgot to comment on your calculation above.
The "Fixed dish angle" specified in the STAB documentation refers to the elevation of a sat to your south. For someone at a 28 deg latitude, this would be 57.3 deg. So your calculation above SHOULD be :

57.3-(45-28)= 57.3-17=40.3

Ie STAB is also using the approximation of using the declination of a southerly sat. I'm not sure where you got the "52" , but you can see that the 57.3 -(-28) is equal to 57.3 + 28= 85.3 ie = 90-declination.
It took me a while to figure out exactly what that crazy equation was doing.

[ahoss2000]

I did not notice that the STAB calculation is for a south sat. I used IA-5 @97 , and the elevation for a fixed dish in my location is 52.

I do not know why my number is off, but I get good signal all the way to Galaxy10R. I do not see a clear marker where I should adjust the dish angle on my Fortec 90CM dish. Right know I read off the number from middle of the LNB arm as seen in the picture:

http://i77.photobucket.com/albums/j6...Picture004.jpg

It would be nice to know where the error is in my system.

Thanks

[Rico.]

Originally Posted by rray32539

The elevation setting on the motor should equal the latitude of your location. If you are at 30 degrees north latitude, set your motor to 30 degrees.

That number and the calculator number do not match ? Can someone please explain.

Thanks,
Rico

[wejones]

Originally Posted by Rico.

That number and the calculator number do not match ? Can someone please explain.

Thanks,
Rico

The calculator doesn't give you a number for the motor elevation (or latitude setting, which is 90 minus elevation), so there is nothing to "match". The calculator gives the value for the DISH elevation, not the motor elevation. Below the calculator it says to set the motor to your latitude, which is wrong BTW, but these calculators apparently use that as a close enough approximation. Really, you should be using a value about 0.6 degrees higher than your latitude, but using your latitude is close enough for most people, particularly since the scales aren't that accurate. However when setting the motor angle, err to the high side, not the low side should be a good rule of thumb.

[Rico.]

Thanks a bunch. I did not know that there was an elevation for the motor and another for the dish - rookie me . I have ordered the motorized dish but have not installed it yet and came here to the forum to get some tips from you experienced folks.

You mentioned that there a error in the elevation setting for the motor, so can you double check my numbers for a stab 90 motor:
Latitude: 28.648
Longitude: 81.298
zip code: 32707 (very close to "ahoss2000" who mentioned that 35 worked but 40 did not)

Dish Elevation (from calculator) : 40.2
Motor Elevation (= Lat + 0.6): 29~29.3

Thanks,
Rico.

[wejones]

Originally Posted by Rico.

..
You mentioned that there a error in the elevation setting for the motor, so can you double check my numbers for a stab 90 motor:
Latitude: 28.648
Longitude: 81.298
zip code: 32707 (very close to "ahoss2000" who mentioned that 35 worked but 40 did not)

Dish Elevation (from calculator) : 40.2
Motor Elevation (= Lat + 0.6): 29~29.3
....

Use the chart at:
http://www.geo-orbit.org/sizeimgs/modpolanglesr.gif

{Or use a calculator I made, at BJDISCALC2 }

for your latitude on interpolation, the latitude setting you should use (which is really 90 minus elevation) is around 29.25. Of course you can't set the scale to that precision, but aim for a bit more than 29, rather than for between 28 and 29.
Now also from either the chart or my calculator, you get a declination of about 4.16. This should be subtracted from 45, which is the bend in the motor shaft for your motor. This would give you 40.84. The 40.2 number from the calculator assumes a declination of 4.8. Notice that you'd be using a motor elevation that is about 0.6 deg less (latitude angle .6 more) which is compensated by using a dish elevation that is about 0.6 deg more, so for a sat to your south, they both give the same angle. However using these modified numbers, the mount will track better on sats to your east or west, because the Sadoun chart assumes that the declination of sats is the same across the arc, which it isn't. Instead, sats to your east or west have about 0.6 deg less declination.

[Rico.]

Thanks very much wejones , I will be installing this weekend, I'll let you know how it goes.

[Rico.]

after I installed I am getting about 80% level but 0% quality? any suggestions?
Thanks,
Rico