Radio Beacon Converter
Posted on Aug 21, 2012 5712
The radio beacon band extends from 280 to 516 kHz. Each beacon has its own characteristic AM`-modulated morse-coded
callsign that is transmitted on a specific frequency. To be able to receive distant beacons, the aerial signal is passed through a band-pass filter that effectively suppresses longwave and mediumwave signals. The filter also converts the aerial impedance, Zm, from about 10 KOhmhm to the input impedance of mixer IC1, which is about 1 KOhmhm. The mixer adds or subtracts the received signal to/from the local oscillator signal so that the beacon signal can be received on a normal shortwave receiver. The resulting frequencies are from 9.72 to 9.48 MHz or from 10.280 to 10.516 MHz. In the construction of the converter, some components must be surrounded by a metal shield, as indicated by dashed lines on the PC board layout. The circuit is aligned with the aid of an SSB receiver, to which the output of the converter is connected. Tune the receiver to 10 MHz and adjust the oscillator frequency of the converter with C8 for zero beat. Next, detune the receiver slightly until you hear a pleasant whistle, which is adjusted for minimum level with the aid of PI. Finally, tune to a beacon transmitting at or about 300 kHz and adjust C13 for maximum sound output.