374 BELL SYSTEM TECHNICAL JOURNAL 



polarized at right angles to the first. Particularly useful are the A90-degree 

 and Al80-degree differential phase-shift sections which produce differential 

 delays between the two polarizations of 90 degrees and 180 degrees, respec- 

 tively. The properties of these sections are discussed, and it is shown how 

 they may be combined to form a phase changer which will transmit substan- 

 tially 100 per cent of the incident power with a phase which is readily ad- 

 justable. Several different methods of building these sections are finally 

 described. 



Considerations in the Design of a Radar Intermediate-Frequency Amplifier.^ 

 Andrew L. Hopper and Stewart E. Miller. The intermediate-frequency 

 amplifier of a microwave radar receiver is commonly required to provide 

 approximately 100 decibels amplification in a bandwidth of 1 to 10 mega- 

 cycles, centered at frequencies in the 30- and 60-megacycle regions. Meet- 

 ing such requirements involves the use of five to ten amplifier stages of the 

 highest efficiency that can be suited to production methods. In addition, 

 the noise figure of the radar intermediate-frequency amplifier is a significant 

 contributor to the over-all radar receiver noise figure, and must therefore be 

 maintained at an absolute minimum. By examining a particular inter- 

 mediate-frequency-amplifier design (one providing an over-all bandwidth of 

 10 megacycles centered at 60 or 100 megacycles), this paper discusses qualita- 

 tively the theoretical problems involved in such a design and gives data of 

 practical importance to the engineer attempting to build a similar amplifier. 

 Measured characteristics of approximately fifty amplifiers are summarized to 

 illustrate the end results achieved. 



Historical ]\ote on the Rate of a Moving Atomic Clock}'^ Herbert E. 

 Ives. The history of the idea of variation of frequency with velocity is 

 followed through Goigt, Larmor, Lorentz, and Einstein. The Michelson- 

 Morley experiment is explainable by any contraction of dimensions in the 

 ratio (1 — i^/c^) A along and transverse to the direction of motion. To 

 each contraction corresponds a different value of frequency change. The 

 theoretical speculations pointing to the relation Vm = Vo{\ — v^/c'^f are 

 discussed, together with the significance of the experimental test by means of 

 canal rays. 



New Low-Coefficient Synthetic Piezoelectric Crystals for Use in Filters and 

 Oscillators.^^ W. P. Mason. Two crystals of the monoclinic sphenoidal 

 class have been found which have modes of vibration with zero temperature 

 coefficients of frequency, high electromechanical coupling constants, and 

 high Q's or low dissipation. These properties make it appear probable that 

 such crystals may have a considerable use in filters and oscillators as a sub- 



» Proc. I. R. E., November 1947. 

 "7o7/r. Opt. Soc. Amer., October 1947. 

 " Proc. I. R. K, October 1947. 



