VHF converter - for short-wave receivers

july/august 1984 A for short-wave receivers Many short-wave listeners often wish their receiver could be extended above 30 MHz. The converter described here makes it possible to add either the 30 . . . 60 MHz or the 60 . . . 90 MHz band to your existing receiver. A converter transforms a certain range of radio frequencies that can- not be processed by a given receiver into one that can. Its output is nor- mally connected to the aerial input of the receiver. The present converter is suitable for the reception of either the 60 . . . 90 MHz or the 30 . . . 60 MHz band. It consists of an r.f. pre-amplifier, an oscillator, and a mixer. The signal picked up by the aerial is applied to a preselector con- sisting of tuned circuit L1-C1-D1, MOSFET amplifier T1, and tuned cir- cuit L2-C2-D2. Diodes D1 and D2 are varactors which enable fine tuning of the two resonant circuits. A varactor is a semiconductor diode operated with reverse bias so that it behaves as a voltage-dependent capacitor. ...