The super regenerative radio receiver was used for many years, particularly at VHF and UHF where it was able to offer simplicity of the circuitry and relatively high levels of performance.
The super regenerative radio is not used much these days, although there are a few niche applications . However in the past it was far more widely used, although care had to be taken to ensure it did not radiate interference.
Super regenerative receiver basics
The super regenerative receiver is based on the simpler regenerative radio. It uses a second lower frequency oscillation within the regeneration loop that interrupts or quenches the main RF oscillation.
The second or quench oscillation typically operates at frequencies above the audio range, e.g. 25 kHz to 100 kHz.
In operation the circuit has sufficient positive feedback to bring it to oscillation. Even a small amount of noise will bring the circuit into oscillation.
How does super regeneration work
An explanation of the operation of the super regenerative receiver starts by looking at a regenerative radio.
The output of the RF amplifier in the receiver has positive feedback applied, i.e. some of the output is fed back to the input in-phase. Any signal present at the time will be amplified repeatedly and this can produce signal amplification levels of a thousand times or more.
Although the gain of the amplifier is fixed, it is possible to achieve gain levels approaching infinity by using positive feedback techniques like this with the circuit on the point of oscillation. In reality, infinite gains are not possible because of issues like phase shifts within the circuit and limiting of the voltage rails.
The regeneration introduces a negative resistance into the circuit and this means that the overall positive resistance is reduced. This means that in addition to the additional gain increases, the selectivity or Q of the circuit is improved.
When the circuit is operated with feedback such that the oscillator runs sufficiently into the region of oscillation, a secondary lower frequency oscillation occurs.
The secondary oscillation breaks up the much higher frequency RF oscillation – periodically breaking up or quenching the main oscillation.
The action of the quenching oscillation, RF signals are able to build up to very high levels. Gain levels can often approach a million or so in a single stage.
The concept was originally discovered by Edwin Armstrong who coined the term super regeneration.
The term has remained and this type of radio is called the super regenerative receiver to this day.
More Essential Radio Topics:
Radio Signals Modulation types & techniques Amplitude modulation Frequency modulation RF mixing Phase locked loops Frequency synthesizers Passive intermodulation RF attenuators RF filters Radio receiver types Superhet radio Radio receiver selectivity Radio receiver sensitivity Receiver strong signal handling
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