Radio Direction Finder:

A radio direction finder can determine the direction from which radio signals come with great precision. By taking two or more readings from radio beacons the navigator can, by using a chart showing the location of the beacons, determine the position of own vessel. Beacons are identified by a code, often a two or three letter Morse code. The codes are shown on the charts. The Radio Direction Finder can also indicate the direction to another vessel, whether the vessels are to meet, and more importantly if a vessel is in distress. 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. Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately, using two or more measurements of known transmitters, the location of a vehicle can be determined. Radio Direction Finder is widely used as a radio navigation system, especially with boats and aircraft. Radio Direction Finder systems can be used with any radio source, although the size of the receiver antennas are a function of the wavelength of the signal; very long wavelengths (low frequencies) require very large antennas, and are generally used only on ground-based systems. These wavelengths are nevertheless very useful for marine navigation as they can travel very long distances and "over the horizon", which is valuable for ships when the line-of-sight may be only a few tens of kilometers. For aerial use, where the horizon may extend to hundreds of kilometers, higher frequencies can be used, allowing the use of much smaller antennas. An automatic direction finder, often capable of being tuned to commercial AM radio transmitters, is a feature of almost all modern aircraft.

ITT Mackay Marine – 4004A

Manufactured by: ITT Mackay Marine

Model: 4004A

Radio Frequencies: 200-550KHz

Radio Corporation of America – AR-8714C

Manufactured by: Radio Corporation of America

Model: AR-8714C

Power Requirements: 115VAC

Radio Frequencies: 190-520KHz

C Plath Hamburg – GPE277

Manufactured by: C Plath Hamburg

Model: GPE277

Radio Frequencies: 240-540KHz, 2.12-2.24MHz

Power Requirements: 220/115VAC, 0.1/0.2 Amp or 24V/12VDC, 0.5/1.0 Amp