Radio Frequency Location Beacons A beacon, transmitting radio signals, to enable a rocket to be located, can be built for less than 20 pounds, and can be made exceedingly simple. The pulse circuit is based on the ubiqutous 555 timer IC, and is arranged to form an astable multivibrator. It was decided to design the circuit so that a regular pulse was output, since a pulsed output is easier to home in on than a constant output. For this circuit, a frequency of around 1 Hz would be easy to detect via the receiver. The choice of the compinent values was also chosen by calculating the lowest possible duty cycle. The duty cycle, is essentially the time the IC is on, and the time the IC is off. The less time the IC needs to be switched on, the longer the battery life can be stretched out. The minimum theoretical duty cycle with a 555 timer is 50%. Running the calculations for a 1 Hz frequency circuit with the lowest duty cycle one can get away with, produces a circuit which has a calculated frequency of 1.05 Hz. For this circuit, the resistor values for R1 was 1000 Ohms, the resistor value for R2 was 68,000 Ohms, and the Capacitor value was 10 microFarads. This produced a duty cycle of 50.36%. Components Component Value/Comments Cost (including VAT) R1 1000 Ohm Resistor 5p R2 68,000 Ohm Resistor 5p C1 10 microFarad Capacitor 15p IC1 555 timer IC 75p Tx 433 MHz Transmitter £14.99 £15.99