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.
Postbulbar ulcer with retrocecal abscess. A case report.
POSTBULBAR peptic ulcers comprise 5% to 10% of all duodenal ulcers. They often present diagnostic and therapeutic problems which are quite different from the usual bulbar ulcer. Ninety-eight percent of postbulbar ulcers occur in the first and second portions of the duodenum and are usually on the posteromedial wall. Characteristic peptic-ulcer pain is the most common symptom. The pain, however, frequently radiates to the back and is often intractable.1-5Hemorrhage is two to three times more common than in bulbar ulcers, is more severe, and less amenable to medical therapy.1,3,4,6,7Perforation with peritoneal contamination is a rare complication of postbulbar ulcers, since they usually penetrate into adjacent organs.2-4This is the case report of a perforated postbulbar ulcer which presented as a retroperitoneal retrocecal abscess. Report of Case A 62-year-old Negro man was admitted to the surgical service on May 20, 1963, with a 24-hour history of