Miniature MW receiver - a matchbox radio to set the world on fire?

The design is based on the MW receiver circuit which was published in March 1981. This circuit lends itself very well to miniaturisation because it requires very few components and the power consumption (0.3 mA) is sufficiently low to allow the use of a small mercury cell. The Ferranti ZN 414 IC is the "heart" of the circuit. This IC is reasonably well known by now, its 3 pin housing con- taining a straight through receiver. The only external components required are the tuning capacitor and aerial. Figure 1 shows a block diagram of the IC; a high impedance input stage, an RF amplifier, an AM detector and an AGC (automatic krn a matchbox radio to set the world on fire ... ? Over the past fifty years a lot of miniature radio circuits have been designed. Unfortunately most of them have suffered from a lack of output power and sensitivity. Furthermore the majority always had problems with the aerial. Readers may remember the wrist watch t...