New modulation techniques for increased efficiency in UHF-TV transmitters
The use of electron-beam modulation in klystron amplifiers is an important means of reducing the electrical power consumption of ultra-high-frequency power amplifiers, employed in the transmission of television signals. This paper explores the characteristics of the amplifiers, describes the methods developed for applying video modulation, and gives details of typical power savings which can be expected.
The television performance of the klystron amplifier
The paper describes the electrical behaviour of multi-cavity klystrons, now extensively used as high-power amplifiers in u.h.f. television transmitters. The factors affecting the frequency response are reviewed, with descriptions of the particular conditions required for output coupling and cavity tuning. The response of the klystron to the television tests for non-linearity is discussed in detail, and it is suggested that (a) differential phase shift is produced by the basic a.m.-p.m. characteristic of the tube; and (b) the discrepancy between observed results of line-rate linearity and differential gain tests is due to differing amplification of single and double sidebands, to be expected with any non-linear transfer characteristic. This discrepancy can be removed by suitable signal processing in the transmitter.
Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode.
A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.