A NEW METHOD OF TELETYPE MODULATION
Abstract
The possibilities were investigated of a modulation system for teletype which distributes the transmitted energy uniformly over a frequency band with the idea that such a system would be less affected by fading and meteors than a frequency shift keying (FSK) system. When fading occurred, noise appeared at only 1 or 2 values of instantaneous modulating voltage, which appearance indicated that the fading was frequency selective in nature. A system of modulation which spreads the transmitted energy over a frequency band does so without increasing the noise bandwidth of the receiver. The optimum linear receiving filter for determining the presence or absence of a transmitted pulse is one whose system function H(epsilon) is the conjugate of the Fourier transform of the time function of the transmitted pulse. The filter can be designed to have an impulse response with the desired broad frequency spectrum without causing S/N deterioration at the receiver. A laboratory model of the system is described; test results indicated that it has definite advantages over FSK. The obvious disadvantage of the system (requirement for large transmission band-width to transmit the samll information rate of a teletype signal) is not too serious in the 30- to 50-mc. region. The greatest meteoric frequency shifts were of the order of 0.004%
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 22, 1952
- Accession Number
- AD0000928
Entities
People
- Donald J. Gray
Organizations
- Massachusetts Institute of Technology