Yaw, pitch and roll vs. azimuth and elevation

[senmeis]

Hi,

Yaw, pitch and roll are used to describe the movement of planes or ships. Azimuth and elevation are used to describe the pointing direction of a dish antenna. Can they be used exchangeably? I think two angles are enough for planes and ships, why 3?

Owen

 

[marcusl]

They don't describe movement so much as attitude, which is the physical orientation of an object relative to some reference coordinate system. You cannot fully define 3D attitude with only 2 coordinates.

 

[phinds]

I think two angles are enough for planes and ships, why 3?

Uh ... you think planes can only move in 2 dimensions?

 

[russ_watters]

I think two angles are enough for planes and ships, why 3?

No, you need 3 axis on planes and ships; telescopes, dishes and solar panels don't need roll, so they only have 2.

 

[russ_watters]

Uh ... you think planes can only move in 2 dimensions?

It's not about moving it's about orientation: 2 axes of orientation is enough to move in 3 dimensions (1 axis for 2 dimensions). You need the 3rd in vehicles just to stay level(roll).

 

[russ_watters]

They don't describe movement so much as attitude, which is the physical orientation of an object relative to some reference coordinate system.

This is true but can be confusing when it comes to pitch, which is used interchangeably at least in shorthand "pitch" or "pitch attitude".

 

[phinds]

It's not about moving it's about orientation: 2 axes of orientation is enough to move in 3 dimensions (1 axis for 2 dimensions). You need the 3rd in vehicles just to stay level(roll).

 

[Ranger Mike]

I sell coordinate measurement machines. These cnc machine tools move in cartesian or polar coordinates. Cartesian system of coordinates use is the X,Y and Z axis where points are describes by x,y and z locations. Polar coordinates describe the location by a distance and azimuth or direction ( usually in degrees from an origin or datum) Elevation describes a location relative to height. ( usually AGL or above ground level or normal to the 0 plane of the X,Y axis along the Z axis.Great video on roll yaw and pitch.

 

[tech99]

Notice that "roll" does not seem to have a meaning for an antenna, except that when we rotate the plane of polarisation we are executing roll.
It is also common to use the terms pan and tilt, as with photography.

 

[senmeis]

One dish antenna system has specs of azimuth and elevation. In addition it also has a roll range. As far as I understand azimuth and elevation are in principle enough for pointing to a direction. With the additional roll it could rotate more quickly. Is it correct?

Owen

 

[tech99]

I imagine the "roll" movement is for adjustment of polarisation, but it is more usual to do this by rotating the feed.

 

[Klystron]

I imagine the "roll" movement is for adjustment of polarisation, but it is more usual to do this by rotating the feed.

The person in this video rotates the feed manually. [Warning: the tech in this video should remove his ring and watch while working on electronics.]

 

[Ranger Mike]

in the " old days" you had one satellite in orbit and elavation and azimuth were enough to align the dish. now you have 3 satellites and you need to ROLL or tilt the dish to get the best possible signal.

 

[tech99]

Why is this?

 

[Ranger Mike]

from wikipedia
It is common to polarize satellite TV signals because it provides a way of transmitting more TV channels using a given block of frequencies. This approach requires the use of receiving equipment that can filter incoming signals based on their polarisation. Two satellite TV signals can then be transmitted on the same frequency (or, more usually, closely spaced frequencies) and provided that they are polarized differently, the receiving equipment can still separate them and display whichever one is currently required.

Throughout the world, most satellite TV transmissions use vertical and horizontal linear polarization but in North America, DBS transmissions use left and right hand circular polarization. Within the waveguide of a North American DBS LNB a slab of dielectric material is used to convert left and right circular polarized signals to vertical and horizontal linear polarized signals so the converted signals can be treated the same.

A 1980s Ku-band LNB (2.18 dB noise figure) without built-in polarization selection and with a WR75 fitting for separate feedhorn and polarizer

The probe inside the LNB waveguide collects signals that are polarized in the same plane as the probe. To maximise the strength of the wanted signals (and to minimise reception of unwanted signals of the opposite polarization), the probe is aligned with the polarization of the incoming signals. This is most simply achieved by adjusting the LNB's skew; its rotation about the waveguide axis. To remotely select between the two polarizations, and to compensate for inaccuracies of the skew angle, it used to be common to fit a polarizer in front of the LNB's waveguide mouth. This either rotates the incoming signal with an electromagnet around the waveguide (a magnetic polarizer) or rotates an intermediate probe within the waveguide using a servo motor (a mechanical polarizer) but such adjustable skew polarizers are rarely used today.

The simplification of antenna design that accompanied the first Astra DTH broadcast satellites in Europe to produce the LNBF extended to a simpler approach to the selection between vertical and horizontal polarized signals too. Astra type LNBFs incorporate two probes in the waveguide, at right angles to one another so that, once the LNB has been skewed in its mount to match the local polarization angle, one probe collects horizontal signals and the other vertical, and an electronic switch (controlled by the voltage of the LNB's power supply from the receiver: 13 V for vertical and 18 V for horizontal) determines which polarization is passed on through the LNB for amplification and block-down conversion.

Such LNBs can receive all the transmissions from a satellite with no moving parts and with just one cable connected to the receiver, and have since become the most common type of LNB produced.

The final alignment that needs to be set is the skew adjustment on the LNB. This is the angle that the LNB itself sits within the LNB holder. Unless the satellites that you wish to align your dish to are perfectly due south (or north down under!) then you are going to need to make an adjustment for the LNB skew. The reason this is so important is because satellite signals are broadcast in both horizontal and vertical polarisations and without setting the skew correctly the LNB and satellite dish will not be able to optimally identify the difference between these and they can interfere with one and another resulting in an unreliable signal, picture pixilation and possible complete loss of signal altogether.

in other words you got to tilt it in for the best signal.

 

[tech99]

Thank you, I had forgotten linear polarisation is used in some cases, I thought it was all circular. Memory problem!

 

[senmeis]

In reality the additional roll axis is introduced to mitigate the so called overhead keyhole effect. Is this a conventional method?