Features of construction of ground beacons DME

All types of radio beacons DME (Distance measuring equipment) with appropriate equipment PS forming the basis radioinformatsiynoho channel measurement distance RSBN-based method of navigation time setting. The transmitter emits board equipment DME pulse pairs encoded request from arbitrary repetition frequency. Signals request takes the ground and sends signals respondent answers detained for 50 ms in the form of coded pairs of pulses, pulses synchronized with a request for a new radio frequency that is different from 63 MHz frequency request (rys.5.14 well).

Ground defendant operates on a continuous pulse required. Equipment defendant after taking the pulse of the request (from zero to 3, 000 pairs of pulses per second) and produces decode addition of pulses that are formed from Noise own generator so that the total number of pulses emitted by radio not exceed 2, 700 pairs per second. This mode protects the radio PRD overload and provides appropriate signals 100 onboard applicants who are in range of the beacon.

Board equipment works in search and tracking. When in search query frequency Fz = 150 pairs of pulses per second, in tracking mode 24 pairs of pulses per second (rys.5.14 well).

In search mode PRM board the aircraft receives all signals ground of the defendant, including pulse response for other aircraft, and selects pulses answers to your own request by an appropriate coincidence circuit, which is based on fully automatic strobe process. The scheme matches the first reception signal from the strobe beacon forms a cyclic (synchronously with the frequency search) increasing its duration for the next pulse, which was adopted, until at least four matches with 10 cycles of the request. Since random sequence of pulses query various different aircraft, the probability of a false choice on your request extraneous radio signal response is close to zero.

Strobe system starts the search when the board PRD adjusted to the new working channel ground when the defendant or the duration of interruption receiving radio beacon exceeds the permissible value.

The search process lasts no more than 20 seconds and stops after recognition confident answers that meet their own impulses request.

Then stroboscopic system goes into tracking mode, during which the measured delay between the time a request emission and reception of signals corresponding signals (adjusted for the value of constant delay of 50 ms) is proportional to the distance of the aircraft to the ground defendant beacon. When working in maintenance mode system provides automatic continuous measurement of the distance of the aircraft from the lighthouse, giving relevant information on the indicator board equipment DME.

To store information in the formation and emission of signals query onboard equipment has a special arrangement of memory that stores the latest information about distance for 10 seconds.

Fig 2.5 The principle of the beacon DME:

a - avionics;

b - Ground equipment

Ground defendant enters a fixed delay time between pulses on request and transfer the corresponding pulse response. Fixed (main) delay time (Main Delay or Fundamental Delay) is introduced so that the approach to the lighthouse in the aircraft airborne equipment had the opportunity to complete the formation and emission of signals coming inquiry to answer to the previous query. Fixed delay in the range of 35... 50 ms does not affect the aircraft providing continuous information about the distance to some hoses that is remote from the location of the defendant on the basis of the delay.

To provide some (auditory) in recognition of the defendant DME beacon signal detection is transmitted every 30 seconds at a speed of approximately 7 words per minute. Signals Recognition formed a special manipulator Morse alphabet that turns off the pulse response and replaces a fixed frequency of 1350 pairs of pulses per second sequence of dots and dashes, which included onboard detected and sent to the headphone driver. Thus during robot through the circuit-board memory gauges distance not interrupt indication information available.