Transceiver YES-97. Amplifier. Scheme, description

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Transceiver YES-97. Amplifier. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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The YES-97 transceiver uses a broadband power amplifier based on two KT931A transistors. Based on the UY5DJ amplifier, published in the magazine "Radio" No. 2-88 on p. 21. Minor improvements were made in it, which affected only certain sections of the scheme.

New quiescent current stabilizers for output transistors have been introduced. Cascades on KT626 transistors act as current generators, providing stabilization of the base current of KT931A transistors, regardless of the ambient temperature. At the same time, KT626 transistors provide an additional, no less important function of amplifiers in the negative feedback circuit of the output transistors. The use of a sufficiently deep OOS makes it possible to obtain a high linearity of the amplifier when operating in a wide range of output powers - from minimum to maximum.

(click to enlarge)

Thermal compensation of the output transistors is provided by the properties of the transistors themselves. It is known that the base-emitter junctions of KT931 transistors (any transistors, approx. RW3AY) are diodes, which in themselves can be good sensors for the temperature of a powerful transistor crystal. Given that the current flowing through the diode is stable, as the temperature increases, the voltage drop across the diode decreases, which, in turn, will lead to a decrease in the base and, accordingly, the collector quiescent current of a powerful transistor. In practice, it turned out that the quiescent current thermal compensation circuit used is so good that no additional thermal coupling of any circuit elements with the output transistor cases is required.

The amplifier was checked and tested using a two-frequency method in the middle of the 20-meter range at a frequency of 14150 kHz, which shows that the power at the peak of the envelope at a load of 50 ohms reaches 100 W, and the level of mutual modulation does not exceed -45 dB.

The power amplifier has a large gain. To provide an output power of 100 W, the maximum input signal level does not exceed 150 mW with an input impedance of the amplifier of 50 ohms.

Actually the design of the amplifier has not undergone any changes. The preamplifier (driver) is assembled according to a push-pull circuit on transistors KT610 and 2xKT904. High-frequency broadband transformers T1 ... T3 completely repeat those from the UY5DJ amplifier, their design and winding data have not changed.

The amplifier circuit has an ALC that maintains a constant output signal and its high quality over a wide range of loads. For experimental purposes, at full output power, the antenna was repeatedly turned off and shorted. The amplifier successfully withstood such "bullying", which characterizes its rather high operational reliability.

The printed circuit board of the transceiver is made of double-sided foil fiberglass 110x80 mm. The foil on all sides of the board is preserved. The tracks are cut with a cutter. Metal tracks, marked with a smooth line, are located on the inside, and with straight lines - on the outside. The appearance of the printed circuit board is shown from the side of the details.

Transceiver YES-97. Amplifier. Printed circuit board

Author: G. Bragin, RZ4HK, Chapaevsk; Publication: N. Bolshakov, rf.atnn.ru

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