TR_CONTROL

Published:2009/7/13 21:43:00 Author:May | From:SeekIC

Used to control low-power transceiver for 20-meter amateur band. Sidetone is obtained from simple relaxation oscillator using GED-13-T programmable UJT. Sawtooth output is attenuated and applied to input of two-transistor audio amplifier. Transmitter keying is done with series switch using 2N4036 silicon transistor. Antenna relay applies +12 V appropriately to transceiver stages used during transmit (+12T) and receive (+12R), and provides switching of antenna between transmitter power chain and receiver RF amplifier. Use DPDT relay with 800-ohm 12-V coil. Transmit receive logic uses μA741C opamp as differential comparator. When key is closed, 2.2-μF capacitor is discharged, making opamp output switch to high state and saturate 2N3904 relay driver, pulling in relay for transmit operation. When key is released, capacitor begins to charge; at 6-V point (about 0.5 s with 220K timing resistor), opamp changes state again and relay opens for receiving.-W. Hayward, Low-Power Single Band CW Transceiver, Ham Radio, Nov. 1974, p 8-17.



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