2-Metre Transmitter

* See text 028 RADIO & TV The transmitter was designed primarily for use by radio ama- teurs as a radio beacon and as such it provides a good quality sig- nal free of unwanted harmonics. Transistor Tl, in association with crystal Xl, operates as a 36 MHz oscillator. Filter Ll -C3 obviates any tendency of the circuit to oscillate at 12 MHz (the fundamental frequency of the xrystal). Circuit L2-C4 is tuned to the fourth harmonic of the oscillator signal (=144 MHz). This signal is fed to the aerial via a buffer stage consisting of T2, a double-gated FET. The (amplitude) modu- lating signal is applied to the second gate of the buffer. The output power of the transmitter has been kept low, about 10-40 mW. The modulating signal is generated by N1, an oscillator that switches the transmitter on and off via transistor T3. The switch- ing rate lies between 0.1 Hz and 0.5 Hz. When the output of N1 is low, T3 is switched off, and the transmitter is inoperative because the supply is disabled....