Super-regenerator with switched LC circuit. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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An oscillator with discontinuous generation at a certain stall frequency can operate as a super-regenerative (super-regenerative or super-regenerative detector) [1] and serve to receive AM and/or FM (broadband) signals. In this case, it does not really matter how the intermittent generation mode is implemented, i.e. how the oscillations of the RF generator are disrupted. For example, it is possible to "short-circuit" the oscillatory circuit of the LC-oscillator (RF self-oscillator) periodically with the damping (superization) frequency using the Kl key (Fig. 1).
(click to enlarge)
However, to obtain a super-regenerative mode, it is necessary to close the switch with a supersonic damping frequency fGS > 20 kHz. Thus, this key must be fast enough. As such a key, the simplest key mixer (for example, on a single bipolar transistor) can be used. Such a key (a mixer in the key mode) "short-circuits" the LC circuit of the RF self-oscillator LkCk under the influence of an external source signal (ultrasonic GSS).
That is why the circuit shown in Fig. 1 may be referred to as a super-regenerator (super-regenerator) with external damping.
To receive signals from the air, an antenna is connected to LkCk through the antenna capacitor CA (small capacitance) (you can also use inductive and other connections with the antenna).
The audio frequency voltage (together with the damping frequency) is removed through the isolation capacitor SRZD from the power supply circuit (DC voltage). The presence of R1 and R2 allows you to remove alternating voltages of audio frequency and quenching frequency (superization). Note that for some circuits, the resistor R2 may be absent.
A blocking capacitor SBL is installed along the power circuit, made up of several RF capacitors (0,22 μF each) and an electrolytic capacitor.
The operating circuit that implements the considered principle of switching the RF LC circuit of the self-oscillator is shown in fig. 2. In this scheme, VT1, together with C1R1R2, forms a simple key mixer that closes the LC circuit LkCk "short" (to ground), thereby disrupting the generation. The data for Lk and Sk are given in [2].
The generation is interrupted (with a damping frequency fGSh) by a signal coming from an external GSS. In this case, fGSh = fGSS.
In order for VT1 to be open (i.e., to "short" LkCk, disrupting RF generation), a voltage of + 0,5 ... 0,7 V is required on the base of this transistor. , in the circuit, the resistor R1 mentioned above was installed, which also performs a protective function (protects the VT1 emitter junction from excessive currents).
Despite the voltage drop across R1, the circuit starts to work as a super-regenerator when the GSS voltage at the circuit input reaches 1V (and even somewhat less). This confirms our assumption about a possible superization mechanism (i.e., UHSS > 0,7 V). The AF signal (together with the superization frequency and HF) is taken from the R3 / R4 divider in the power supply circuit of the RF oscillator, made on VT2 and VT3. Further, the signals go to the buffer stage, low-pass filter and low-pass amplifier, made similarly to [2].
It is interesting to note that the presence of a key mixer (VT1) and a local oscillator (ultrasonic GSS) that controls this mixer make the circuit (Fig. 2) somewhat similar to the superheterodyne circuit.
(click to enlarge)
However, in this case, we have exactly a super-regenerator, which, as usual, hisses in the absence of a received signal (super noise is clearly audible).
As the tests have shown, the sensitivity of this superregenerator is not lower than the sensitivity of the receiver [2] (at fGSS = 20...50 KHz).
Literature
- Zherebtsov I.P., Radio engineering. - M.: Svyazizdat, 1963.
- Artemenko V. Superregenerative receiver. - "Radio amateur. KB and VHF", 2004, No. 1, p.36-37.
Author: V.Artemenko, UT5UDJ, Kiev
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