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Focal length of parabolic dish |

Start: Find you latitude.

Latitude is 53.71

Input this to the calculator https://www.satsig.net/ssazelm.htm together (optionally) with the longitude, say 1.85. If you input your longitude put the same value for the satellite orbit location as this will give additional azimuth-elevation angles for a hypothetical satellite due south of you.

Example assuming: The results from the polar mount satellite dish pointing calculator say:

The MAIN MOTOR AXIS BEARING ANGLE M must be 54.4 degrees.

The SMALL DOWNWARD TILT ANGLE of the dish must be 7 degrees.

Mis-aligned initial situation was as above:

Viewed from the west, facing east. North is on the
left, south is to the right. The actuator is centralised. **Note the
sloping yellow line which is the polar axis < very important**.

The main polar angle M is currently set to 56 degrees. This is quite close. It needs adjusting by 1.6 deg to 54.4 deg.

The cranked stub from the motor on this model of mount (Stab HH100) is tipped forwards by 30 deg (I think!) relative to the polar axis line, and the elevation scale on the dish is presently set to 38 degrees, so the beam is tipped upwards by (38 - 30) = 8 degrees, which is completely wrong.

Other types of polar mount motor may have the stub arm cranked forwards by various angles, including say 30, 40 or 46.5 deg.

The small downwards tilt of the dish should be 7 degrees so the angle on the dish elevation scale needs to be set to ( 30 - 7 ) = 23 deg.

The dish elevation scale needs readjusting from 38 to 23 deg.

Having set these two angles the entire assembly needs slight unclamping at the pole and rotating, till it is aimed exactly due south.

► Page created 7 Nov 2005, amended 24 Feb 2015. Eric Johnston |