HF communications receiver with few components - covers large range by superhet principle with oscillator operating above or below receiving frequency

摘要

The HF communications receiver (200-2000MHz) reduces number of components by using those already present for other functions as well as their normal ones. The local oscillator frequency can be varied in stages of eg 1, 10, 100 kHz by a varactor diode circuit, in the case of a receiver with a synthesiser. The first IF frequency is an integral multiple of 50 MHz. The oscillator is operated above or below the receive frequency by an amount equal to the IF frequency spacing. Then the whole range of frequencies can be covered by a small number of partial ranges.