Satellite Tracking

Overview and status

Old system based on RC2000C system often goes out of limits and lose track. I decide to design system that will keep track well.

• Pros
  • Can run without expensive beacon receiver, it can get signal source over SNMP from Newtec receiver. Also you get update of TLE over Internet.
  • You can set various parameters to save motor resource or prefer keeping signal within some limit (+-1db)
  • You can collect and monitor telemetry data

• Cons
  • Require computer and RS-422 converter.

Short explanation of principles

First run

Run search, use TLE as hints for movement. (E.g. we already know that satellite should move East and Up. Do plain "signal peaking" algo.)

In case hints permanently wrong N continuous times, reverse counter by software (sometimes when we go UP, Elevation counter decreasing, instead of increasing.

By TLE find 2 maximum far points for elevation and azimuth. Then calculate "gear ratio", e.g. Elevation in 2 far points in "counters" of RC2000C(reed sensor in motor?) is 100, and difference in angle 10 degree, means ratio s 10 "counts" per degree.

Store AGC data in specific positions as reference, and store possible database or EL/AZ counters to degrees relation.

TODO: Is counter is not straight linear to angle degree? Depends on way how motor mounted. I should research more about that.

Operational run

We calculate current azimuth and elevation of satellite, we suppose it is peak signal. Calculate when satellite will move out from antenna beamwidth. (Note: by default beamwidth specified for 3db, i want to keep, for example, 1db, calculate it). It will be a time when next move scheduled. By gear ratio calculate next move, note also maybe you will need to make more poor signal tracking, if next position is just 1-2 steps (my case, because antenna setup on my customer doesn't move well for 1-2 steps, and error ratio is too bad).

Calibrations

At most distant from "center" of lemniscata (2 points, for EL and for AZ), do plain search, to verify if AZ/EL relation to degree is correct. It is possible that it will not, in case system has cumulative errors, or moved by wind.

Precautions

• Wind can be detected by huge delta (MinMax) during measurement.
• Use N(?) percentile method to cut off wrong values, especially during instability of measurements caused by wind. Averaging just doesn't work in this case!
• Bad weather, search window

Real job

The system is written, and it works even much better than existing in RC2000C program. Setup is "problematic" is because mount of the dish have too bad precision, e.g. each step of motor in y axis is 0.033 degree, and x axis is even worse. Antenna beamwidth is 70/(450/2.5) = 0.38degree. RC2000 moves with precision up to - 1 step, means sometimes if you move 2 steps, you will move in reality 1 step. That's can become big issue.

Another benefit - it doesn't need external signal source, such as beacon receiver, i just wrote RMCP reader and getting signal directly from Newtec receiver. Note, it will work only on satellites with AGC.