spot frequency receiver

Cilt72 spot frequency receiver Monitoring a number of frequencies in the short-wave band, such as the international shipping distress fre- quency, is a fascinating pastime. Since only a limited number of stations is normally monitored, and their frequency is invariably fixed by international treaty, the receiver needs only to be capable of being switched between those spot frequencies. The receiver works on the direct con- version principle, i.e., the oscillator frequency is equal to the received fre- quency, so that the intermediate fre- quency is zero. The aerial signal is fed to tuned RF amplifiers Ti and T2via a switched preselector. The RF amplifiers are coupled to an S042P type mixer. There are three crystal-controlled local oscillators, which are switched into circuit in accordance with the pre- selector. The output of the mixer is the audio signal, which is fed to AF ampli- fier IC2via low-pass filter R11. R 13- C28•••C30. The gain of IC2is about 60 dB. Part of the o...