The regenerative circuit, an early radio design, is still used in simpler devices today. It involves powering the output of a vacuum tube or transistor and amplifying a signal through a tuned circuit. Drawbacks include difficulty tuning and interference. Modern applications include RFID readers and keyless locks.
The regenerative circuit is an early type of design used in radio transmitters and receivers that is still in limited use today. At the most basic level, the concept involves powering the output of a vacuum tube or a solid-state component such as a transistor itself. Combining this with a specially tuned circuit can greatly amplify a signal without the need for expensive add-ons. There were also drawbacks to receivers that made use of regenerative circuitry, such as difficulty tuning in to new stations and the fact that they could also create interference by acting as transmitters. These circuits were used extensively in radios up until the 1940s, although their use in modern times has been relegated to radio frequency identification (RFID) readers and other simpler devices.
A basic regenerative circuit consists of only a few components. The main component is an active element, such as a vacuum tube or field effect transistor (FET), which acts as an amplifier. A signal is passed into the bead and then passed through a tuned circuit. The tuned circuit only allows a certain resonant frequency into the active element, creating a feedback loop that can greatly amplify a signal. Since vacuum tubes were both expensive and cumbersome when regenerative circuits were introduced, this design allowed for the creation of less expensive and smaller radios.
One major disadvantage of the regenerative design is the way the feedback loop interacts with signal gain. Every time you change stations on a regenerative radio, you need to adjust the feedback level. Failure to observe this precaution could result in improper operation. Radios with these circuits also tended to suffer from noise pollution as a direct result of the simple regenerative amplification design, and could even generate powerful interference when used as transmitters.
Most radios stopped using the regenerative circuit in the 1940s, although it is still found in simpler devices. Garage door openers that send out simple radio frequency (RF) signals typically use a regenerative circuit since they are so cheap and compact. These modern circuits typically use field-effect transistors or other solid-state components instead of vacuum tubes. Other modern applications of regenerative circuitry include radio frequency identification readers, keyless locks, and receivers in some cell phones. These are all applications where the compact nature of a regenerative circuit outweighs the various design drawbacks.
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