High efficiency frequency converter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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High efficiency frequency converter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Mixers, frequency converters

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The frequency converter, the circuit of which is shown in fig. 1 provides a high dynamic range for the transceiver. It consists of two keys on diodes V4-V11, connected in a bridge circuit, and a control unit. The connection between the control unit and the keys is transformer (T1).

Elements D1.1 and D1.2 from the sinusoidal voltage of the local oscillator form rectangular pulses with a front steepness of not more than 2 ns. These pulses are then amplified by a differential amplifier based on transistors V2, V3. The converter is balanced with a resistor R1, which determines the equality of the durations of negative and positive control pulses. Transformer T1, structurally made with a short-circuited coil, ensures the connection of the amplifier with diode switches with minimal distortion of the control pulses. Resistors R12-R15 limit the maximum current through the public key, and the voltage falling on them, which is the reverse for the private key diodes, determines the maximum amplitude of the input signal to be converted. Obviously, the input and output of the converter are mutually reversible. It is not necessary to ground the DC input of the converter.

Fig.1 (click to enlarge)

This converter was tested as a receiver mixer with a low-noise IF gain path and an electromechanical filter at the input. The mixer output was matched to the EMF by a transformer. A crystal oscillator at a frequency of 5,2 MHz was used as a local oscillator. The following results were obtained.
The sensitivity at a signal-to-noise ratio of 10 dB was 1,8 μV. The level of the converted useful signal dropped by 1 dB when the level of the interfering signal, located outside the passband of the IF path, reached 1,6 V (rms).
The level of intermodulation components of the 3rd order (according to the method described in the journal "Radio", 1981, No. 3) was no more than -100 dB. The latter parameter can be improved by 6...10 dB by using a low loss IF filter such as a crystal and a higher sensitivity IF amplifier.

In a differential amplifier, it is desirable to use transistors with the same coefficient h21e. KT355A transistors can be replaced with KT368 with any letter index. Instead of D1.1 and D1.2, you can use the logic elements "OR-NOT" of the K500 or K100 series with any number of inputs. If a high-speed trigger is used in the control pulse shaper, then the local oscillator frequency should be twice the required one. Balancing is carried out automatically.

High efficiency frequency converter
Ris.2

The case of transformers T1 and T2 with a short-circuited turn (see Fig. 2) is brass, preferably with a silver-plated surface. Longitudinal cuts for conclusions are made along it. All windings are made on separate ring magnetic cores made of M2000NM1 ferrite (size K 12x5x5,5). The windings are insulated from the core with varnished cloth or fluoroplastic tape. Winding I at T1 and T2 contains 10 turns (removal from the 5th turn), winding II - 5 turns of PELSHO 0,12 wire, evenly distributed on the ring. The data are given for the local oscillator frequency range of 2 ... 30 MHz (for lower frequencies, the number of turns must be increased), while the output impedance of the signal source and the load resistance for the converter must be within 50 ... 75 Ohms. All resistors in the converter are MLT-0,125, capacitors are K.M-6.

The transmitter must be mounted with the best possible symmetry and careful shielding. The power circuit must be high-frequency isolated. These measures are needed to reduce the emission at harmonic frequencies of the local oscillator.

Authors: V. Drozdov, UA3AAOJ, S. Zhukov, UA3ACV, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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