ABSTRACTS OF TECHNICAL ARTICLES 375 



stitute for quartz, which is difficult to obtain in large sizes. These crystals 

 are ethylene diamine tartrate (EDT) having the chemical formula 

 C6H14N2O6, and di-potassium tartrate (DKT) having the formula K2C4H4O6 

 - i H2O. 



The paper describes the properties of EDT, since this crystal has been 

 found more advantageous than DKT. The 13 elastic constants, the 8 pie- 

 zoelectric constants, and the 4 dielectric constants have been measured over 

 a temperature range, and from these measurements the regions of low tem- 

 perature coefficients and high electromechanical coupling have been located. 

 Six low-temperature-coefficient cuts have been discovered and the properties 

 of these cuts are given. These cuts are being applied in the crystal channel 

 filters of the long-distance telephone system, and may be applied to the 

 control of oscillators. 



Multi-Channel Carrier Telegraph}"^ A. L. Matte. Discussion of a car- 

 rier telegraph system, adapted specifically to railway requirements, to meet 

 the needs for high-quality line transmission. 



Reflex Oscillators for Radar System}^ J. O. McNally and W. G. Shep- 

 herd. The advantages to be gained in the operation of radar systems at 

 very high frequencies have led to the use of frequencies of several thousand 

 megacycles. Operation at these frequencies has imposed serious problems 

 in obtaining suitable tube behavior. Because of the difficulty in obtaining 

 amplification at the transmission frequency, the r.f . section of the usual radar 

 receiver consists of a crystal converter driven by a beating oscillator and 

 operating directly into an i.f. amplifier. Since the midband frequency of 

 the latter has commonly been either 30 or 60 Mc, it has been necessary to 

 provide beating oscillators operating at frequencies differing from those of 

 the transmitter by only a few per cent. 



For radar systems intended to operate at approximately 3000 Mc, which 

 were under development in the early days of the war, it was found that tri- 

 odes then available gave unsatisfactory performance. Attention shifted to 

 the possibility of using velocity-modulated tubes, and the particular form 

 known as the reflex oscillator came into general use. 



In this paper the requirements on beating-oscillator tubes for radar sys- 

 tems are discussed, and the design features w^hich have made the reflex 

 oscillator eminently satisfactory in this application are pointed out. Prob- 

 lems encountered in such oscillators are outlined, and the solution in a num- 

 ber of cases is indicated. In some instances military requirements and ex- 

 pediency were in conflict with the optimum performance, and hence certain 

 compromises were necessary. 



^ Railway Signaling, December 1947. 

 I'Proc. /. R. E., December 1947. 



