The general problem of obtaining oscillations by the use of diodes with critical electron transit time is outlined, Some of the properties of a 10 em. oscillator tested experimentally are included. Extraneous losses were reduced when the oscillator was enclosed within a wave guide.T H E theory of the production of negative impedance by means of an electron discharge between two parallel planes has been known for some years.' The negative resistance appears whenever the electron transit time is approximately 1~, 2~, 3~, etc. cycles of a given high-frequency current. Using this property, Muller was able to construct tubes giving 100 em. oscillations," The operating efficiencies were quite low, and in the frequency range covered by these tubes it seems fairly conclusive that other methods of producing oscillations are more effective than the critical transit time diode. However, there is promise in the application of diode operation to much higher frequencies than those of Muller.In a diode where the electron discharge occurs between two parallel planes where one performs the function of electron emitting cathode and the other constitutes an anode biased at a positive potential, the effective impedance presented to an external source is inherently low in magnitude. This is because of the capacitance between the two planes which causes the decrease in impedance at high frequencies. For the production of oscillations, the capacitance must be combined with a resonant structure having the proper inductance to resonate at the desired frequency and having a resistance which effectively is less in magnitude than that of the electron stream. Because of the low losses thus required of the coupling or tuning circuit the properties of concentric lines and of tuned cavities offer a favorable method of attack. These structures also have the property that the impedance presented to the diode proper may be made low to match its capacitive reactance at the high frequencies desired.The two most important sources of circuit resistance are ordinary ohmic loss modified in the usual way by skin effect in the conducting 1 For numbered references see end of paper. 280

This paper describes a microwave circuit designed for use with the 1553‐416A close‐spaced triode at 4000 m.c. It presents data on tubes used as amplifiers and modulators and concludes with the results obtained in a multistage amplifier having 90 db gain.

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This paper describes some of the results of the work of the Joint Development and Research Subcommittee of the National Electric Light Association and Bell Telephone System on the mutual impedances of ground‐return circuits. The first part of the paper deals with some experiments which were performed to establish an experimental background for the testing of theoretical ideas. Different theories, one involving an “equivalent ground‐plane,” a second a d. c. distribution in the earth, and a third an a. c. distribution in the earth, are discussed in the light of the experimental results. While none of these is adequate to explain all the observed phenomena, each has a field in which it can be made useful. The second part of the paper is devoted to a description of practical means for predetermining the mutual impedances of power and telephone lines. This involves an experimental determination of a curve of mutual impedance as a function of separation in the region of the proposed exposure and the calculation of the overall mutual impedance between the proposed lines from this curve and the dimensions of the exposure. The results of trials of this method in two locations are given which indicate that itshould be of sufficient accuracy for engineering purposes.

the new angles are used instead of the new impedances. V. Find T en from (22) using e Qn just obtained. VI. Determine e in from ( %dn %dn \ / % dn % qn \ T _ ~ , j -β *η I -_ χ i J ( 56 )qn ·»άη / \ * qn ^ an / This formula is obtained by combining (8) and (9) VII. Calculate change in e* n from where Δ t is the increment of time used for one step; Ε n is the average slip ring volts, during the Δ t con sidered; ei"is the value of the synchronous stator voltage at the beginning of the Δ t considered; T on is the open circuit time constant of the machine; and Δ e* n is the change which takes place in e* n during the Δ t con sidered. This formula 9 comes directly from the well known relation that the applied voltage is equal to the resis tance drop plus the inductive drop, the quantities being all in per unit values.VIII. Calculate new value of e* n from e* n found in II and Δ e* n found in VII. e* n = e* n + Δ e*n (58) new II.VII.IX. Calculate change in angle from (55). The other angular changes are to be calculated as explained in the discussion of (55), (54), and (51).X. Allow the angle to shift and repeat IV to X. Appendices I and II of the paper will be devoted to illustrating the procedure by means of a special exam ple. The general procedure is modified in this special case for convenience in illustrating fully each step. Synopsis.-This paper describes some of the results of the work of the Joint Development and Research Subcommittee of the National Electric Light Association and Bell Telephone System on the mutual impedances of ground return circuits.The first part of the paper deals with some experiments which were performed to establish an experimental background for the testing of theoretical ideas. Different theories, one involving an "equivalent ground-plane, 11 a second, a d-c. distribution in the earth, and a third, an a-c. distribution in the earth, are discussed in the light of the experimental results.While none of these is adequate to explain all the observed phenomena, each has afield in which it can be made useful The second part of the paper is devoted to a description of practical means for predetermining the mutual impedances of power and telephone lines.This involves an experimental determination of a curve of mutual impedance as a function of separation in the region of the proposed exposure and the calculation of the over-all mutual impedance between the proposed lines from this curve and the dimen sions of the exposure.The results of trials of this method in two locations are given indicating that it should be of sufficient accuracy for engineering purposes.