axes for dish antennas

[senmeis]

Hi,

a ship based dish antenna consists of 4 axes: elevation, azimuth, pol and roll. As far as I know the first three are necessary for antenna direction. Why roll? Is it used to accelerate the direction finding on the ship (against ship roll)?

 

[betwixt]

I'm no expert on this but I would guess it refers to the axis passing through the COG of the ship which would be necessary to calculate the offset needed to compensate for pitching and rolling of the ship body.

Brian.

 

[wwfeldman]

following brian's lead, i'll jump in
see the drawings in

What are the "azimuth and elevation" of a satellite? | Memorial Spaceflights

www.celestis.com

elevation and azimuth will let you point your antenna in any direction

pitch and roll are the angles related to motion of the ship
pitch is the angle along the length of the ship, measured from the horizontal
roll is the angle along the width of the hip, measured from the horizontal.

don't know what pol is

for completeness sake, airplanes have a third angle, called yaw
yaw is the angle the plane points measured from its forward direction of travel
ships generally point int he direction of travel whereas airplanes are more free to yaw

 

[betwixt]

Again guessing 'pol' is polarization, rotation of the dish antenna along the axis it is pointing. It does change as the angle of the dish mount moves from vertical but it would only need dynamic correction in extreme circumstances. More likely it would be to adjust polarization to compensate for the ships latitude and longitude and hence the skew from the angle of signal source.

Brian.

 

[senmeis]

Pol is polarization axis. I doubt pol and roll are redundant as far as rotation goes. Maybe the performance are different.