
RF circuits and techniques 251
output bandpass filter. Figure 8.23(c) shows the receiver's first LO (local
oscillator) radiation as received on a 418 MHz whip, and for comparison,
the radiation from a super-regenerative receiver operating at about 330
MHz (where there is no allocation for such devices) is also shown. It is the
receiver unit of a remote radio doorbell which is widely offered for sale in
the UK by postal mail order.
Super-regenerative receivers performed useful service in the Second
World War but thankfully faded from the scene afterwards. They are
unpleasant devices, transmitting a broad band of interference centred on
thei