Published Resources Details
Journal Article
- Title
- An experimental Frequency-Modulated broadcast transmitter
- In
- Journal of the Institution of Engineers, Australia
- Imprint
- vol. 20, no. 9, Sep 1948, pp. 107-117
- Description
This paper, No. 964, originated in the Sydney Division of The Institution, and was presented before a General Meeting of the Electrical and Communication Engineering
Branch of the Division, on 22nd October, 1947.The authors are on the staff of the Research Laboratories, Amalgamated Wireless (Australasia) Ltd.
This paper was awarded the 1947 Electrical Association Premium, Institution of Engineers Australia, in 1949.
- Abstract
A description is given of a 250-watt f.m. broadcast transmitter which complies with the requirements of the American Federal Communications Commission "Standards of Good Engineering Practice Concerning F.M. Broadcast Stations." The equipment described includes the frequency-modulator unit, power-amplifier unit, aerial array, and station monitor. The frequency modulator depends for its operation upon the time delay which occurs when a f.m. signal is passed through a multi-section band-pass filter. A signal from a fixed-frequency source is mixed with an f.m. signal from a reactance-valve modulated oscillator; the f.m. difference-frequency component is selected, and after passage through a time-delay
network, is once more mixed with the original f.m. signal.
The difference-frequency component in the output of this second mixing stage has the same centre frequency as the fixed source and is phase modulated; pure frequency modulation is obtained if the audio input is passed through an inverse-frequency network before application to the modulator. In an experimental unit, a maximum phase-angle deviation of approximately ± 5 radians is obtained at a fundamental frequency in the vicinity of 300 kc.; a frequency multiplication of 324 times yields an output in the 88 to 108 Mc. band with a deviation of ± 75 kc.