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This short-wave converter, which doesn’t have a single coil requiring alignment, is intended to enable simple medium-wave receivers to be used to listen to short-wave signals. The converter transforms the 49-m short-wave band to the medium-wave frequency of 1.6 MHz. At the upper end of the medium-wave band, select an unoccupied frequency that you want to use for listening to the converted short-wave signals. Good reception performance can be obtained using a wire antenna with a length of one to two metres. Short-Wave Converter  Circuit Diagram The converter contains a free-running oscillator with a frequency of around 4.4 MHz, which is tuned using two LEDs (which act as variable-capacitance diodes!) and a normal potentiometer. The frequency range is set by adjusting the emitter current using a 1k trimpot. The oscillator frequency depends strongly on the operating point. This is due to the combination of using an audio transistor and the extremely low supply voltage. Under these con...

Superregenerative receivers are characterised by their high sensitivity. The purpose of this experiment is to deter-mine whether they are also suitable for short-wave radio. Superregenerative receivers are relatively easy to build. You start by building a RF oscillator for the desired frequency. The only difference between a superregenerative receiver and an oscillator is in the base circuit. Instead of using a voltage divider, here we use a single, relatively high-resistance base resistor (100 kΩ to 1MΩ). Superregenerative oscillation occurs when the amplitude of the oscillation is sufficient to cause a strong negative charge to be applied repeatedly to the base. If the regeneration frequency is audible, adjust the values of the resistors and capacitors until it lies somewhere above 20 kHz. The optimum setting is when you hear a strong hissing sound. The subsequent audio amplifier should have a low upper cutoff frequency to strongly attenuate the regeneration signal at its output whi...

Make a simple and easy electronic fuse for dc short circuit protection. This is an electronic fuse that protects the load against short circuit. Relays must be chosen with a voltage value equals to the input voltage. Don’t omit using the 100uF capacitor with appropriate voltage value with respect to the input voltage. If you can’t provide, you can use C106 instead of BRX46. Electronic Fuse for DC Short Circuit Protection: You can adjust the current with using 10K potentiometer. If you will use the fuse with very high currents, lower the 0R6 5W resistor value (ex. 0R47, 0R33, 0R22 or 0R1). Watt value of the resistor should be increased also.