Titley Electronics:EPIRB: RX3-DF EPIRB

Products > EPIRB > RX3-DF Direction Finder

EPIRB RX3-DF Direction Finder

The 121.5 MHz EPIRB DF equipment consists of the Model RX3-DF receiver mounted onto its antenna. The antenna provides the desired directional properties and the receiver provides the necessary means of hearing the signals in order that the direction to an activated EPIRB may be ascertained. The audio signals from the receiver, which are used by the operator to indicate the direction to the EPIRB, are heard from the internally mounted weatherproof speaker as well as optional lightweight headphones. The battery is located inside the receiver, accessible by undoing the two knurled screws on the rear cover. For training of operators, the Model RX3-DF receiver has the ability to receive a signal from a TEST EPIRB transmitting a signal on 121.4 MHz.

The antenna is constructed largely from aluminium and incorporates a handle for ease of operation in the field. Four flexible antenna element extensions are screwed to the "stub" elements for normal operation. These flexible extensions spring back to their correct positions should they be snagged on external objects. The extensions are normally removed when the unit is stored or transported. The radio is housed in a rugged die cast aluminium case. The connection between the radio and the antenna is made by a concealed coaxial cable, which lies inside the square section tubing of the main antenna shaft.

The radio is crystal locked to the 121.5 MHz EPIRB frequency (121.4 MHz in TEST MODE) and is a double conversion superheterodyne design. It incorporates a voltage controlled oscillator (VCO) function which provides an audio tone which increases in pitch as the received signal strength increases. This function serves to greatly assist the direction finding ability of the system. To also assist in the direction finding ability of the system, there is a signal strength meter on the front panel.

An on board microprocessor has two functions. Firstly, it monitors the battery voltage and if the voltage falls below a preset voltage, an audible tone is used to indicate to the operator of the low battery condition. Secondly, it monitors the RESCUE or TEST FREQUENCY mode of the receiver and in the TEST FREQUENCY position it outputs an audible tone and flashes a front panel indicator to indicate to the operator the frequency that the receiver is currently looking for is a signal from a TEST EPIRB transmitting on 121.4 MHz.

Sensitivity for 10 dB S+N/N 110 dBm with 30% AM at 1 KHZ signal (1.0uV into 50 Ohms)

Gain control range 50 dB minimum

Nominal input impedance 50 Ohms

Frequency range 121.5 MHz Search Frequency OR 121.4 MHz Test Frequency

Frequency selection Selected by a toggle switch at the rear of the receiver under the rear cover Test Frequency selection indicated by audio warning beeps

Intermediate frequency 10.7 MHz and 455 KHz

Audio output Internal loudspeaker and external headphones

Battery supply 9.6 Volt PP3 type alkaline type disposable cell

Battery life Approximately 10 hours operation at mid volume levels

Low battery voltage 7.9V DC indicated by an audio warning beep

Battery current 50 mA at mid volume, mid gain setting

Signal strength display Front panel analogue meter, approximately 20db dynamic range

Size 80 x 45 x 150 mm (H x W x D) approximate

Weight approx. 330g plus weight of the aerial

Case construction Aluminium extrusion with plastic end caps

Sealing The case design minimises the intrusion of dust, dirt or spray. All external joints are either overlapping or sealed

Front panel Reverse printed polycarbonate panel incorporating a signal strength meter

Circuit technology Surface mount on double side plated through FR4 board. Re-flow soldered