The early 1920 radio transmissions/ telegraph messages and early 2 way radio devices capable of Receiving and transmitting signals without the use of wires were called T.S.F. in France. If you were near enough to a broadcaster you could pull in a signal from the air with considerable cost and effort. This acronym covered both the receivers and transmitters that were used at home or in a cumbersome mobile format that could be used from a stopped vehicle. After selecting a high point, the apparatus consisting of Antennas, Batteries, Optional Speaker or more often Headphones and the Receiver or Receiver/Transmitter would require hook up with a maze of wires. There were also smaller portable crystal radios but, they were a far cry from the current day smart phone with stereo high end earbuds. For more details the following is from Wikipedia: A crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no other power source but that received solely from the power of radio waves received by a wire antenna. It gets its name from its most important component, known as a crystal detector, originally made from a piece of crystalline mineral such as galena.[1] This component is now called a diode. Crystal radios are the simplest type of radio receiver[2] and can be made with a few inexpensive parts, such as a wire for an antenna, a coil of copper wire for adjustment, a capacitor, a crystal detector, and earphones.[3] They are distinct from ordinary radios as they are passive receivers, while other radios use a separate source of electric power such as a battery or the mains power to amplify the weak radio signal so as to make it louder. Thus, crystal sets produce rather weak sound and must be listened to with sensitive earphones, and can only receive stations within a limited range.[4] The rectifying property of crystals was discovered in 1874 by Karl Ferdinand Braun,[5][6][7] and crystal detectors were developed and applied to radio receivers in 1904 by Jagadish Chandra Bose,[8][9] G. W. Pickard[10] and others. Crystal radios were the first widely used type of radio receiver,[11] and the main type used during the wireless telegraphy era.[12] Sold and homemade by the millions, the inexpensive and reliable crystal radio was a major driving force in the introduction of radio to the public, contributing to the development of radio as an entertainment medium around 1920.[13] After about 1920, crystal sets were superseded by the first amplifying receivers, which used vacuum tubes (Audions), and became obsolete for commercial use.[11] They continued to be built by hobbyists, youth groups, and the Boy Scouts[14] however, as a way of learning about the technology of radio. Today they are still sold as educational devices, and there are groups of enthusiasts devoted to their construction[15][16][17][18][19][20] who hold competitions comparing the performance of their home-built designs.[21][22] Crystal radios receive amplitude modulated (AM) signals, and can be designed to receive almost any radio frequency band, but most receive the AM broadcast band.[23] A few receive shortwave bands, but strong signals are required. The first crystal sets received wireless telegraphy signals broadcast by spark-gap transmitters at frequencies as low as 20 kHz.[24][25]