called “microphonics” which is a phenomenon where almost anything in the physical circuitry of the receiver can act as a sort of microphone or audio sound pickup. Touch or bump such radios and you will hear a thump or ring in the speaker or earphones. Still another problem is that of AC line hum whenever an unregulated power supply is used rather than batteries.
The Ramsey HR40’s use of the SA602 integrated circuit chip offers a circuit configuration that is as immune as any simple superhetrodyne to the classic problems with Direct Conversion receivers. The receiver is not as easily overloaded by the VOA or Radio Moscow broadcasts, and there are few annoying ”microphonics” or incurable AC hum.
Circuit Description:
U1 combines a
HR40 • 6