Dilshan R Jayakody’s Web Log

This post is about beat frequency oscillator (BFO) module which is used to receive SSB and CW signals from the ordinary shortwave receiver. The original circuit which is related to this post is obtained through the internet and we modify it to get more precise output with commonly available electronic components. ( Unfortunately at the time of writing this original link is no longer accessible due to a dead link. ) This module consists of two general purpose NPN transistors and we select 2SC828 because of its availability in the local marketplace. For the crystal, we use commonly available 455 kHz ceramic resonator. Assembled 455 kHz BFO module. This BFO unit is easy to construct and may not need any test instrument for calibration. To receive the SSB signals, power this unit with regulated 5V or 6V DC power source and place BFO module near to the shortwave radio receiver. To get good results to place output wire of BFO near to the IF amplifier section of the target receiver....

This is two transistors and two IF transformer based superheterodyne receiver which is designed to receive 13m to 41m bands. With quite good external antenna this receiver performs similarly to the commercially available shortwave receiver and its audio quality is at a very satisfactory level. Prototype version of two transistor superheterodyne shortwave receiver. This receiver can be constructing on PCB, breadboard or commonly available veroboard or stripboard. For tuning use Polyvaricon or air variable capacitor. For precision tuning, connect small trimmer capacitor with parallel to variable capacitor’s gangs or use mechanical wheel assembly with the variable capacitor. This receiver is designed to work with 9V regulated power supply and it requires an external AF amplifier to drive the headphone or speaker. In our testing, we use a TDA2050 audio power amplifier with this receiver. With small wire antenna, this receiver is capable to receive most of the stations which in...