FM pocket radio - with just six transistors

with just six transistors To the best of our knowlegde this is the simplest FM radio that can be made. Not only that but it also works quite well, even if the sen- sitivity does not seem very good. The principle of this receiver may ap- pear somewhat unusual to some. It is based on a "synchronizable oscillator" consisting of transistors T2 and T3 that is synchronized to the received frequency by means of T1. This transistor operates as a wide- band HF preamplifier for the FM band. In principle this amplification stage could be omitted and the aerial C2 connected directly to capacitor C4, cer but the sensitivity would then be 5V greatly reduced. The oscillator is tuned by capacitor C5 to about 87 . . . 108 MHz and, because of the synchronization already mentioned, the frequency shows the same variations as the signal picked up by the aerial. These frequency variations, of course, rep- resent the AF information. The AF information is extracted by the simple expedient of considering ...