QRPP transceiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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Among radio amateurs there are more and more adherents to work on QRP (up to 10 W) and QRPP (up to 1 W) equipment. At the same time, a process is underway not only to improve the methods of working on the air, but also to create transceivers that are simple in design, but reliable enough for communication.
(click to enlarge)
On fig. 1 shows a diagram of the simplest telegraph QRPP transceiver for operation on the 10-meter band, developed by UB5UG. It consists of a generator on a transistor VT1, a mixer on a diode VD3 and a low-frequency amplifier (transistors VT2, VT3). This is how the transceiver works. When receiving (switch S1 in the "RX" position), the oscillation amplitude of the quartz local oscillator on the L1 coil is limited by the VD1 diodes. VD2 to a level of 0,3 V. The level is chosen so that the amplitude of the second harmonic of the heterodyne voltage, isolated by the L3C3 circuit, is sufficient for the normal operation of the mixer. When transmitting, the diode VD1 is closed, the diode VD2 is connected in series with high-resistance headphones BF1 (resistance of about 1 kOhm) and does not shunt the coil L1. The voltage on the coil is maximum, and the transceiver generates maximum power into the antenna. Thanks to the diodes VD1, VD2, the voltage frequency generated by the cascade on the transistor VT1 differs by hundreds of hertz during transmission and reception, as a result of which communication with a similar transceiver is possible (auditory reception of telegraph signals is possible).
For greater gain, it is recommended to add an amplifier to the transceiver (Fig. 2).
In this case, the capacitor C2 and the coil L2 can be excluded. The number of coil turns L2 should be related to the number of coil turns L3 as 1:12, L4 to L1 as 2:11. L5 to L3 as 1:3. The tap for the L1 coil is made from 1/11 of the turns, for L4 from the middle.
Coil data:
L1 - 2+22 turns
L2 - 1 turn
L3 - 12 turns
L4 - 2x3 turns
L5 - 4 turns
The circuits are made on rings 30VCh 7x4x2 wires PEVTL 0,27.
Author: UB5UG; Publication: N. Bolshakov, rf.atnn.ru
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