The development of radio transmission and reception is one of the major technical achievements of the twentieth century. The impact of voice broadcasts to the public, whether by commercial stations or government-run organizations, have expanded the horizons of everyday citizens in virtually every country on earth. It is hard to overestimate the power of radio broadcasting.

Technology has dramatically reshaped the transmission side of AM and FM broadcasting. Profound changes have also occurred in receiver technology. Up until 1960, radio broadcasting was basically a stationary medium. The receivers of that time were physically large and heavy, and required 120 V ac power to drive them. The so-called portable radios of the day relied on bulky batteries that offered only a limited amount of listening time. Automobile radios incorporated vibrator-choppers to simulate ac current. All the receivers available for commercial use during the 1940s and 1950s used vacuum tubes exclusively.

The first technical breakthrough for radio broadcasting was the transistor, available commercially at reasonable prices during the early 1960s. The transistor brought with it greatly reduced physical size and weight, and even more importantly, it eliminated the necessity of ac line current to power the radio. The first truly portable AM radios began to appear during the early 1960s, with AM-FM versions following by the middle of the decade.

Many of the early receiver designs were marginal from a performance stand-point. The really good receivers were...