3.3 - The basic circuits
In spite of its better sensitivity they still had some disadvantages such as the production of annoying hisses during the tuning process. In 1912, Edwin H. Armstrong invented a new type of circuit known as regenerative circuit in which the AUDION behave like an amplifyer as well as a generator of electromagnetic waves. Either the TRF as well as the regenerative circuits were big steps in radio receivers' development when operating for tuning in low frequencies. However, with the growing of the radio broadcasting stations now operating in frequencies higher than 10 MHz those types of receivers had difficulties to detect them. In the early twenties Armstrong again invented a new type of circuit now known as superetherodyne circuit. Such kind of circuit was more selective and stable and so became the base for the manufacturing of all types of radio receivers. In 1930, started radio boom and later in 1933 appeared in the market a new circuit known as frequency modulation or FM. Invented by the so famous Armstrong in this new system it could eliminate the phenomenon of static found in the conventional amplitude modulation.
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