Radio beacon transmitting apparatus

1,025,101. Amplitude modulated radio transmitters. VIDOR HOLDINGS Ltd. April 17, 1962 [April 17, 1961], No. 13786/61. Headings H3R and H4L. [Also in Division H2] An amplitude modulated radio transmitter for use in radio beacon apparatus, comprises a crystal controlled transistor oscillator size 1, a frequency doubler valve amplifier stage II and a frequency doubler valve power amplifier stage III. The signal is amplitude modulated by providing the valves with a square-wave pulsed H.T. supply, via a half-wave rectifier 36, from a push-pull transistor oscillator stage IV comprising PNP transistors 28, 30 and a saturable transformer 3 including primary, output and feedback windings 33, 34 and 38, respectively, operating at a frequency of 1 kc. The positive battery tap on the primary winding of the transformer is positioned so that transistor 30 conducts for three times the conduction period of transistor 28, hence the oscillator output square waveform is asymmetric and the transmitter valves provide maximum output for three-quarters of each modulation cycle. The stage IV is triggered on for 0À5 seconds and off for three seconds by an astable multivibrator 40, comprising transistors 39, 41, and a switching transistor 42 which periodically supplies forward bias to the bases of transistors 28, 30 to overcome the reverse bias provided by battery 44. During the periods between pulses and when stage IV is triggered off, the valves are supplied from a 12-volt battery source connected in series with output winding 34 and transmit c.w. at low power.