User's Manual

Table Of Contents

USER MANUALNORMARC 7050

MARKER BEACON

A-1

PART V APPENDIX

A ANTENNA TYPE NM 3561 / NM 3562

A.1 Antenna NM 3561 / NM 3562 For Ils Marker Beacon

The NM 3561/NM 3562 Marker Beacon Antennas are log-periodic dipoles possessing proper-

ties of high gain and directivity, and low side lobes. The performances og the antennas con-

form to ICAO Annex 10 item 3.1.6, and are such that they are largely independent of

environment factors such as rain, snow and ice, and they can therefore be located at «diffi-

cult» sites. The directivity of the antennas can, if required, be even further increased by add-

ing additional elements to the array.

The radiation patterns for the antennas are almost unaffected by the surrondings, and the

antennas are therefore suitable for offset location where tilting of the antennas is necessary in

order to obtain the required signal coverage. (Refer to figure A-1)

Figure 12-10, 12-11 and 12-12 shows constant field strenght lines through points in the glide

path (GP angle 3º). The marker beacons are located vertically beneath the localizer course

line at distance of 1050 m (middle marker) and 3.9 nautical miles (outer marker) from the

threshold. The field strengths specified are relative to the maximum level directly above the

antenna. The figures show that for an aircraft travelling at a speed of 50 m/s (96 knots) within

the maximum allowable course sector of 6º the duration of the visual indication will be within

the prescribes limits. The instrument panel lamp should be adjusted so as to switch on or off

at the levels indicated in the figures i.e. -27 dB to -33 dB for Figure 12-10, -11 dB to Figure 12-

11, and -13 dB to -25 dB for Figure 12-12.

The marker beacon antennas are mounted on poles, with the dipoles parallel to the course

line. The rear end of an antenna should be at least 2 metres above the ground.

The NM 3562 antenna comprises two elements, and is fed via a distribution network (DIA 726)

which splits the transmitter power into two equal parts. The network is a coaxial cable hybrid

housed in silumine box together with the monitor network which is used to combine the signal

from the two monitor probes.