Patent GB-738256-A (GB)
Title: Improvements in or relating to space-charge wave tubes
IPC: H03C1/32
Filed: 1953-12-23
Abstract: 738,256. Phase-difference measurements. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Dec. 23,1953 [Dec. 24, 1952], No. 35826/53. Class 37. [Also in Groups XL (a) and XL (c)] A space charge wave tube operating with crossed electric and magnetic fields has an input delay line and an output delay line each facing negative electrodes, and between the two pairs of electrodes so formed is disposed a further pair of electrodes which are not designed as delay lines and which amplify the space charge wave as set out in Specification 692,705, [Group XL (a)], the transverse variation (across the E beam) of - necessary for the operation of the H tube being achieved by the presence of the travelling space charge wave (which is preamplified by the interaction between the beam and the input delay line). In one form, Fig. 1, the beam is subjected to crossed electric and magnetic fields in the space between positive electrodes 8, 11, 13 and negative electrodes 7, 12, 14, electrodes 8, 13 also functioning as input and output delay lines. Electrodes 11, 12 do not function as delay lines. Matched terminations 13a, 19 are provided. The electrodes are carried by insulating supports from a rectangular metal envelope. In modifications, Figs. 4, 6 (not shown), the tube of Fig. 1 is bent into circular form with either the positive or the negative set of electrodes on the outer periphery. The polepieces may be apertured at their centre to allow the passage of the input coaxial line. In a further form, Fig. 8, the cylinder 23 serves as the negative set, and baffle type delay line, 108, 113 and cylinder 111, the positive set of electrodes, and 110 is the gun producing an annular beam. The magnetic field is produced by a D.C. current flowing through electrode 23. The delay lines may carry standing instead of travelling waves. At least one of the electrodes 11, 12, Fig. 1, is insulated from the other electrodes so that the gain can be varied by varying the potential difference between 11, 12, and preferably both electrodes are so insulated. The variation is achieved by potentiometers, Fig. 9 (not shown) and preferably the potentials of both electrodes are varied simultaneously by unequal amounts. The output is amplitudemodulated by applying a modulating voltage, which may be sinusoidal or pulses, to either or both of electrodes 11, 12, Figs. 12, 13 (not shown). If the modulation is applied to both electrodes 11, 12 with a relative phase displacement, the gain is a function of the phase displacement and the tube can be used as a phase discriminator. For automatic gain control the D.C. voltage is applied to the collector 17 and to electrode 11 through a resistor, Fig. 14 (not shown). Thus when the collector current increases the potential of electrode 11 falls, due to the voltage drop across the resistor, so that the gain increases. In a limiter, Fig. 16 (not shown), electrode 12 is connected to the D.C. source via a resistor so that electrons collected by 12 reduce its potential and consequently reduce the gain. If the input signal amplitude increases so do the number of electrons collected by 12 so that the gain decreases further, while if the signal amplitude decreases the gain increases. In another form, Fig. 17 (not shown), the output is coupled to a transmission line housing a detector, and thence via an amplifier and resistor to electrode 11. Thus when the output power increases electrode 11 becomes more positive, due to increase of current in the resistor, and the gain decreases, and vice versa. Noise in the beam and " fading " of the input signal may be compensated in this manner. Since the output power depends on the beam current a limiting effect obtains because the number of electrons captured by 11 increases with increasing intensity of the input signal; the desired limit can be adjusted by varying the D.C. voltage between electrodes 11, 12 which varies the number of electrons captured by electrode 11. In a frequency changer, Fig. 20 (not shown), preferably for a relay station, a low-frequency voltage of frequency F2 is applied to electrode 11 and the input signal of high frequency F1 to delay line 8, the output frequency being F1ŒF2. Since the output and input frequencies only differ slightly the delay lines 8, 13 may be identical. The beam velocities at the input and output ends can be made different, i.e. equal to the phase velocities of the waves of frequencies F1 and F 1 - F 2 so that the output line if dispersive will select the frequency F1 - F2. In a frequency multiplier, Fig. 23, the input and output delay lines may c have the same " delay rate " (i.e. - where v= v retarded wave velocity, c=velocity of light) for the frequencies Fo, nFo respectively so that the beam velocity is the same throughout, or as preferred the beam has different velocities equal to the respective phase velocities of the two waves. The latter is accomplished by spacing 13, 14 further apart than 7, 8 so that the transverse electric field and therefore the electron velocity is smaller at the output than at the input end. The transition between the two electron velocities is obtained by adjusting the voltage between 11, 12, or by progressively increasing the distance between 11 and 12 as shown. To achieve correct coupling in the output space C it is necessary to reduce the potential of delay line 13 slightly by adjustable voltage #Vo.