FIRST TRANSMITTER

One of the first simple radio transmitters I constructed was a combination of 2 circuits
I'd found in c1966 electronics magazines.

RF oscillator: Kalitron type circuit from English Practical Electronics (Sept 66),
RC transmitter for model boat.

Modulator: single TO3 power transistor megaphone from Electronics Australia (Dec 66)

Microphone is a low impedance carbon-button type as used in domestic telephones of the time.
The loudspeaker in the megaphone circuit is replaced by a 4 Ω : 400 Ω 'speaker' transformer
and serves as a form of high level modulation of the +ve supply rail to the oscillator.
Despite the fact that the oscillator is 'cut' for ~27.1 MHz,
and the only portable receiver I had was a Sony AM/FM transistor radio.
the signal could be heard on a couple of spots in the FM band !
I suppose the 'kalitron' oscillator was "rich in harmonics"
Modulation wasn't the best, but it did work and field tests
with an assistant showed it worked OK for at least 500-1K metres or more.

Practical Electronics mag' scan (click to view)

Electronics Australia mag' scan (click to view)

© 1Q 2020