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Encoder for Azimuth Change Pulses

Figure 1: An old encoder uses in the “ASR-910” ATC-radar

Figure 1: An old encoder used in the “ASR-910” ATC-radar

Encoder for Azimuth Change Pulses

A mechanical or optical controlled “encoder” is mounted at the revolving part of the antenna. This encoder produces “Azimut Change Pulses” (ACP's). These impulses are counted either in the monitors (e.g. at the ASR–910) or in the signal processing computer (e.g. at the RRP–117).

The counter gets a reset by a so called North Reference Pulse (NRP) once per revolution. The counting of the pulses will be start again at this moment. Therefore a definite bearing position is determinable.

It is a number of impulses usually between 4096 (this corresponds to a precision of 0.087 degrees per impulse) and up to 16384 (this corresponds to a precision of 0.02129 degrees per impulse).

The direction of bearing information is usually defined “clockwise”.

Decoder wiring
Counter
(12…
 14 Bit)
NRP
Reset
ACP
Clock
A0…A11 (…A13)

Figure 2: Principle of decoder wiring

Counter
(12…14 Bit)
NRP
Reset
ACP
Clock
A0…A11 (…A13)
NRP ACP cnt bus

Figure 2: Principle of decoder wiring
(interactive picture)

The decoder wiring consists of counter circuits, counting the incoming ACP's. The counter will be reset by the North-Reference-Pulse. The absence of a couple of ACP's can be ignored, cause this failure will be terminate by beginning the next turn. If the NRP is missing a longer time, then the error of the absentee ACP's will be added. The whole picture will be turn left.

Figure 3: Encoder (dismantled) providing 16384 pulses per rotation of the antenna's turn table

Figure 3: Encoder (dismantled) providing 16384 pulses per rotation of the antenna's turn table