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A radio direction finder (RDF) is a device for finding the direction, or bearing, to a radio source. The act of measuring the direction is known as radio direction finding or sometimes simply direction finding (DF). Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately ...
Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.
The operator rotated the antenna, looking for points where the signal either reached a maximum or, more commonly, suddenly disappeared or 'nulled'. A common RDF antenna design is the loop antenna, which is simply a loop of wire with a small gap in the circle, typically arranged to rotate around the vertical axis with the gap at the bottom. [3]
At least four antennas are mounted in a precise geometric pattern, often on the roof of a vehicle. Specialty electronics computes the amount of Doppler shift present in the received signals and determines a probable direction from which the signal originates. The direction is commonly displayed using LEDs oriented in a circle or a straight line.
More modern aviation ADFs contain a small array of fixed aerials and use electronic sensors to deduce the direction using the strength and phase of the signals from each aerial. The electronic sensors listen for the trough that occurs when the antenna is at right angles to the signal, and provide the heading to the station using a direction ...
Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse.
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A Bellini–Tosi direction finder (B–T or BTDF) is a type of radio direction finder (RDF), which determines the direction to, or bearing of, a radio transmitter. Earlier RDF systems used very large rotating loop antennas , which the B–T system replaced with two fixed antennae and a small rotating loop, known as a radiogoniometer .