Regenerative HF receiver. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Regenerative HF receiver. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / radio reception

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Despite the widespread use of superheterodynes, regenerative radios continue to attract the attention of radio amateurs. With a simple circuit solution, they allow you to create a design that is easy to adjust with sufficiently high parameters (selectivity, sensitivity). We bring to the attention of readers a regenerative HF receiver.

The described 2-V-1 direct amplification receiver is designed to operate in the short wave broadcasting range of 25 m (11,7 ... 12,1 MHz). It was created as an experiment to further study the properties of an autodyne synchronous receiver. Therefore, you can get acquainted with the theoretical part of this problem by reading the article by V. T. Polyakov [1]. The circuit diagram of the receiver is shown in the figure.

Regenerative HF receiver

The first stage of the high-frequency amplifier is a regenerative Q-multiplier with a high-speed automatic regeneration control system.

The input oscillatory circuit is made up of the inductance of the loop antenna WA1 and the capacitances of the capacitors C6 - C10. Within the specified operating frequencies, it has a very high quality factor, so the effective effective height of the loop antenna can reach several tens of meters. An antenna with such parameters is capable of receiving rather weak signals. The limiting moment on the sensitivity of the receiving device can be the intrinsic noise of the input stage transistor, so it is preferable to use a low-noise transistor in it (the quality factor). In its absence, good results can also be obtained from the widespread and cheap KT315B transistor.

The automatic regeneration control device includes a second stage of a high-frequency amplifier based on a VT2 transistor and a diode detector, consisting of elements C11, VD1, VD2, C13. The initial bias current for silicon diodes and at the same time for the transistor VT1 is created by resistors R1, R2 and R6. The constant component from the output of the detector forms a corrective effect on the regenerative stage, and the variable component through the capacitor C12 in the form of audio frequency signals is fed to a single-stage audio frequency amplifier based on the VT3 transistor. The load of this amplifier is high-impedance headphones BF1 (for example, TON-2). The output power of the amplifier is about 1 mW.

The stabilization of the modes of transistors VT2 and VTZ is carried out using automatic bias resistors R4 and R9, respectively. It is desirable to choose the resistance value of the resistor R4 so that the voltage at the collector VT2 is close to half the voltage of the power source.

The coil of the WA1 loop antenna is frameless, has an inner diameter of 200 mm, contains two turns of copper wire with a diameter of 1,5 mm, wound with a pitch of 10 mm. For rigidity, the turns are fastened together with inserts made of dielectric material. The coil leads are screwed to the insulating support. If a radio amateur has a 20VCh ferrite rod, you can try to make a ferrite magnetic antenna, but its efficiency will be worse than that of a frame antenna.

The receiver uses fixed resistors MLT-0,125. Variable resistor R8 type SP3-1, but any other will do. Capacitor C4 oxide of any type, with an operating voltage of at least 6 V. Trimmer capacitor C6 type KPK-M or KPK-1. The variable capacitor C7 can be made independently according to the recommendations of the descriptions in [1, 2] or used with other limits of capacitance change, for example, 4 ... 180 pF, but connect a ceramic capacitor with a capacity of 18 ... 22 pF in series with it. It is also possible to use a varicap as a tuning element, however, this will somewhat reduce the quality factor of the input circuit. In addition, an additional power supply with a voltage of 15 ... 20 V is required to power the varicap. Capacitors C8 - C10 are ceramic KD or KT (any modification and design options). The remaining capacitors are small-sized ceramic of any type. The capacitance of the capacitor C12 is within 0,25 ... 1,0 uF. As a low-noise transistor in the regenerative stage, you can use KT325A, KT368A, KT399A, KT3106A, KT3120A.

The author did not develop a printed circuit board for the experimental version of the receiver, the mounting of the hinged elements on the same insulating stand to which the coil of the loop antenna was attached.

By selecting the capacitor C10 and adjusting the tuning resistor R8, the regenerative stage is stable at the excitation threshold. This is facilitated by the automatic regeneration control system, which monitors the state of the regenerative cascade and applies a corrective action to the base circuit of the transistor VT1 through resistors R6 and R1. Trimmer resistor R8 must be of high quality. Otherwise, the noise of the resistor will interfere with the operation of the receiver. In the absence of a good quality trimming resistor, a fixed resistor should be selected instead. The frequency boundaries of the reception range are set by capacitor C6.

The total current consumed by the receiver is approximately 3 mA, so a fresh 3336L battery is enough for 500 hours of receiver operation.

The proposed version of the receiver well receives signals from distant radio stations and, compared to a simple superheterodyne, provides a cleaner reception due to the narrow-band and directional properties of the loop antenna, the absence of mirror and interference interference. True, these advantages are realized if there are no powerful interfering radio stations.

The disadvantages of the receiver include the deterioration of the parameters of the loop antenna when massive objects approach it and the dependence of the tuning of the regenerative stage on the level of the supply voltage.

Literature

Polyakov V.T. Autodyne synchronous receiver. - Radio, 1994, No. 3, p.10.
Borisov V.G. Young radio amateur. Ed. 5th. - M.: Energy, 1972, MRB.

Author: S. Kovalenko, Kstovo, Nizhny Novgorod Region

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