QRP transceiver for 80 m. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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QRP transceiver for 80 meters. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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This transceiver is designed to operate as a telegraph in the amateur band of 80 m. A quartz-frequency stabilized oscillator assembled on a VT5 field-effect transistor (see figure) is used both in the receiving and transmitting paths and performs, respectively, the functions of either a local oscillator or a master oscillator. The quartz resonator is connected to the XS4 socket. Within small limits (depending on the parameters of the resonator and the elements of the circuit L1C12), the operating frequency of the generator can be changed by a variable capacitor C12. Usually it is not difficult to "shift" the oscillator frequency by 2...3 kHz.

From the circuit L2C13, through the coupling coil L3, the radio frequency voltage enters the base circuit of the transistor of the output stage VT4. The manipulation is carried out in the emitter circuit of this transistor with a key connected to the XS3 socket. The output circuit L5C9 is matched to the collector circuit of the transistor VT4 and the load (antenna) coupling coils L4 and L6. Transistor VT4 operates without initial bias (in mode C).

QRP transceiver for 80 meters

The receiving path of the transceiver is assembled according to the direct frequency conversion scheme. When the key is not pressed, the VD1 diode is opened by the current determined by resistors R9 and R8. The signal from the antenna, received through the L6 coupling coil into the L5C9 circuit, passes freely into the circuit of the first gate of the VT3 field effect transistor, which operates as a mixing type detector. The RF voltage of the crystal oscillator is applied to the second gate through capacitor C11. The mixing voltage at this gate is determined by the divider formed by resistors R10 and R11.

The variable resistor R8 performs the functions of a signal level regulator in the receiving path.

The audio frequency voltage released on the primary winding of the transformer T1 is amplified by a two-stage amplifier based on transistors VT1 and VT2. The load of this amplifier is head phones with emitter resistance of 1600 ... 2200 Ohm. connected to socket XS1. To increase the volume of radio signal reception, the emitters are connected in parallel.

Coils L1-L6 are wound on frames with a diameter of 6 ... 8 mm (from television receivers) with trimmers made of carbonyl iron. The windings are made of copper wire with a diameter of 0,3 mm in enamel insulation. The number of turns of the coil L1-60, L2 and L5 - 50 each, the rest - 12 each. The communication coils (L3, L4 and L6) are wound over the corresponding contour coils, the winding is ordinary, solid. Transformer T1 - matching from a transistor broadcasting receiver. Capacitor C12 should have a maximum capacitance of approximately 400 pF and possibly a lower initial capacitance.

The establishment of the transceiver begins with the transmitting path. An antenna equivalent is connected to the XS2 socket - a resistor with a resistance of 75 or 50 Ohms and a dissipation power of 1 W. By temporarily short-circuiting the coil L1 and setting the rotor of the capacitor C12 to the position corresponding to the maximum capacitance, the trimmer capacitor C3 achieves the maximum emitter current of the transistor VT4 (a control milliammeter with a full deviation current of 200 ... 250 mA can be connected, for example, to the XS3 socket). Then, the trimmer capacitor C9 achieves the maximum radio frequency voltage on the antenna equivalent. The current consumed by the output stage should be about 150 mA. If the output power of the transmitter is noticeably less than 0,7 W, the number of turns of the coupling coils should be selected (primarily L5 and L6).

When setting up the receiver, it makes sense to select the resistor R10 and capacitor C11 according to the maximum sensitivity of the receiving path. In the audio frequency amplifier, resistors R2 and R3 are selected according to the voltages on the collectors of transistors VT1 and VT2 (2 ... 3 and 5 ... 7 V, respectively).

Transistors BC109 can be replaced with KT342, KT3102 and similar ones; 40673 - on KP350; BF245 - on KP303 or KP302; 2N2218 - on KT928; diode 1N4148 - on KD503 and similar ones.

Author: Hartiikka J. Tippradio; Publication: N. Bolshakov, rf.atnn.ru

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