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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Goodness multiplier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception A prefix that allows you to increase the sensitivity and selectivity of the receiver due to positive feedback without altering it. The quality multiplier is an underexcited generator of electrical oscillations with positive feedback, the value of which can be changed. If the operating mode of the generator is chosen such that the compensation of active losses in the oscillatory circuit is incomplete, then self-excitation of oscillations will not occur, but the quality factor of the circuit will be very large. When such a circuit is included in the resonant amplifier of the receiver, the selectivity can increase by several tens of times. Most often, Q-multipliers are included in the intermediate frequency amplifier. The Q-multiplier itself is made as a separate structure with leads for connecting it to the receiver. Below are several Q-multiplier (QM) schemes that can be widely used in various receivers to improve their quality characteristics (sensitivity, selectivity, bandwidth control). Figure 1, right (II), shows a schematic diagram of the UD, designed for superheterodyne receivers with an intermediate frequency of 1600 kHz. On the left (I) is a diagram of the mixer. The Q-multiplier is connected to the mixer through capacitor C2. The LC and L1C1 circuits must be tuned to an intermediate frequency. Positive feedback is provided through C3.
The emitter current of the transistor, which determines its amplifying properties, can be smoothly controlled by a variable resistor R2. When the emitter current is low, the effects of the POS are weak. With a gradual increase in the emitter current, the effect of the PIC increases due to an increase in the amplifying properties of the transistor, and, finally, at a certain feedback value, the generator is excited. When receiving radio stations operating by telephone, resistor R2 sets the operating mode of the UD near the generation threshold. As a result, the quality factor of the L1C1 circuit increases dramatically. Since this circuit is connected in parallel with the LC circuit of the mixer through the capacitor C2, the selectivity and gain given by such a mixer in a narrow frequency band also increase dramatically. If you bring the UD to self-excitation, then it will work like a second local oscillator; in this case, the bandwidth of the mixer can reach 500 Hz or less. In this mode, the receiver can receive telegraph radio stations. The UD is turned off by switch B1. If, when receiving stations operating by telephone, the value of positive feedback is changed, it is possible to regulate the bandwidth of the intermediate frequency path over a fairly wide range. For an intermediate frequency of 1600 kHz, the L1 coil is wound on a polystyrene frame with a diameter of 7,5 mm with an SCR-1 core (you can use a frame from the IF circuit of the Rubin-102 TV). It contains 35 turns of PEL 0,1 (x4) wire wound in bulk in four sections 3 mm wide. Distance between sections - 2 mm. If it is intended to use this UD scheme in a receiver with an IF of 465 kHz, then the L1C1 circuit must also be tuned to this frequency. On fig. 2 shows a UD circuit on a single transistor for use in superheterodyne-type tube receivers. As the circuit L1C1, one of the circuits of the first IF filter of the receiver is used, into which the DD is introduced. The necessary positive feedback between the emitter and collector circuits is provided by a capacitive C2C3 divider.
Considering that connecting the UD to the L1C1 circuit detunes the latter, the capacitance of the capacitor C1 must be reduced so that the resonant frequency of the IF circuit remains the same. R1 - to select the operating mode of the transistor for direct current. The selectivity (bandwidth) of the receiver is regulated by R3 (the depth of the POS is changed). The selectivity adjustment limits are determined by the resistance R4. The power supply of such an UD is made from the winding of the power transformer of the receiver using a half-wave rectifier assembled on diode D1. Choke Dr1 is wound on a frame (Fig. 3) made of polystyrene.
It contains 100x6 turns of PEL 0,1 wire, the core is SCR-2. As a choke, you can use any coil with an inductance of the order of 3 ... 3,5 mH. On fig. 4 shows a diagram of the UD, made on a lamp L1 type 6N3P. In essence, such a multiplier is a two-stage amplifier with deep negative feedback, complemented by a frequency-selective positive feedback circuit. According to this scheme, high-frequency generators are often assembled. The load of the left triode of the lamp is the L1C1 circuit included in the anode circuit of the receiver mixer. The PIC is fed to the control grid of the right triode through capacitor C2 and resistor R1. The depth of negative feedback is changed by a variable resistor R4. At a certain position of the R4 slider, the POS may become more negative.
When the UD is at the excitation threshold, the quality factor of the L1C1 circuit increases sharply, and consequently, the selectivity and sensitivity of the entire receiver will increase, and the bandwidth of the IF path will narrow. The UD is turned off by switch B1. Resistor R3 to limit the limits of change in selectivity. Structurally, the UD is placed as close as possible to the first IF filter of the receiver. A simple UD, made on an L1 6S1P lamp (Fig. 5), unlike those previously considered, is installed not in the IF path, but at the input of the receiver. Such an DD is recommended to be installed in simple superheterodynes with HF bands to reduce interference from stations operating at frequencies close to the image channel. UD represents an underexcited generator, made according to the scheme with inductive feedback.
The L1C1 circuit is the input circuit of the receiver. The circuit is connected to the input of the RF amplifier or, in its absence, to the input of the mixer. In the UD circuit, this circuit is connected through the capacitor C3 to the control circuit of the grid of the lamp L1. L2 is the receiver-antenna coupling coil. It is connected to the anode circuit of the lamp through capacitor C2. The power supply of the anode circuit of the lamp is parallel, through the inductor Dr1. Adjustment of the depth of the PIC, and consequently, the selectivity is made by the resistor R4, which changes the slope of the lamp. The greater the steepness of the lamp, the stronger the PIC, which means the higher the quality factor of the circuit; the quality factor determines the selectivity of the input circuit of the receiver. Dr1 is wound on a frame with a diameter of 3,5 mm made of organic glass. The inductor winding consists of three sections connected in series, containing: the first - 10, the second - 20 and the third - 70 turns of PELSHO 0,12 wire. The first section is wound in one layer, coil to coil. The width of the second and third sections is 4 mm each, winding in bulk. Distance between sections - 3 mm. The beginning of the first section is connected to the anode of the lamp. When installing the UD, it is necessary to ensure the minimum length of the connecting conductors. When establishing the coupling coil L2, it is necessary to connect it to the anode of the lamp so that when the cathode of the lamp is closed to the housing, undamped oscillations occur in the circuit L1C1. If there is no generation, you need to swap the conclusions of the L2 coil. An interesting DD scheme for use in communication and broadcast receivers of a superheterodyne type with an intermediate frequency of 465 kHz is shown in Fig. 6. Such an DD can operate both in the selection mode, which increases the selectivity and gain of the entire receiver, and in the notch, when a narrow band is "cut out" from the total bandwidth of the intermediate frequency path. Rejection allows you to "cut" interference from the signal, for example, an interfering carrier of an AM signal or a telegraph station. In this case, the noise can be weakened by a factor of 300...500, and the "cut" band can reach 150...200 Hz.
The prefix, in the form of which the UD is drawn up, is connected to the anode of the receiver mixer lamp using a piece of coaxial cable 0,5 m long. UD is made on the right triode of the lamp L1 type 6N2P according to the scheme with capacitive feedback. The oscillatory circuit L1C4C5C6C7 is tuned to an intermediate frequency. A phase-inverted cascade is assembled on the left triode.
The inductor L1 is wound on a standard three-section frame, which is placed in 600HN ferrite cups with a diameter of 8,6 mm. It contains 25x3 turns of PEL 0,12 wire. You can use the FPF from the Selga, Etude and other receivers that have a 1000 pF capacitor in the circuit. As a choke Dr1, you can use 2 ... 3 coils from 465 kHz IF circuits connected in series.
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