Transistor radios

I was listening to Van Morrison's classic hit "Brown Eyed Girl" and the line about transistor radios always appeals to me as I am fascinated by how song lyrics capture science and technology of the era.  Another example is the song "Kodachrome" by Paul Simon and I have written about fractals in the song "Frozen" in an earlier post. When I was younger, I built a crystal radio receiver and was amazed that I can listen to AM radio stations with a device that has no external power source and is powered solely by the energy in the radio waves! I also had a vintage transistor radio that is shaped like a pack of Marlboro cigarettes and powered by a 9V battery. The potentiometers for volume and channel have such a satisfying feel. The transistor radio was born as transistors have supplanted vacuum tubes in the demodulation and amplification circuitry of a radio receiver, resulting in portable receivers that are much smaller and use much less power. Today, portable radios are so much smaller and is packed with integrated circuits as more signal processing is done in the digital domain. The goal of software defined radio (SDR) is to replace all analog signal processing with digital signal processing done by computer algorithms by moving the analog to digital (A/D) conversion as early as possible. However, current computer processors and A/D converters do not have the speed and bandwidth to process digital samples at RF frequencies, so some analog processing is still done in SDR to demodulate the signals to intermediate frequencies or baseband frequencies. So the transistor is still necessary in radios today. But then again, even if the ideal SDR, where all processing is done by software, is possible, since computer processors today are still filled with transistors, technically the term "transistor radios" will be here to stay for a long time!