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A special form of cathode-ray tube used as a frequency multiplier. The output radiated from the dipole, aerial has a frequency four times greater than the input from the source O.
Most of the modern development of the cathode-ray tube is so closely bound up with scanning in television that one is apt to overlook its utility in other directions. The Figure, for instance, shows an ingenious scheme for using its as a frequency-doubler in ultra- short-wave signalling.
The ordinary fluorescent screen is replaced by an annular electrode P, formed of a strip of insulating material bounded by inner and outer conducting wires, which are connected respectively to the two limbs of a Lecher-wire coupling to a dipole aerial. Inserted at intervals along the insulating strip are a series of small 'targets', connected alternately to the inner and outer conductors, so as to feed intermittent pulses of energy from the cathode ray to the aerial.
The discharge stream through the tube is focused, as usual, by a negatively-biased cylinder C, so as to pass through the centre of the anode A. Once past the anode the stream comes under the influence of a pair of deflecting plates which cause it to trace out a circular path over the annular target.
Ultra short-wave oscillations from a source O are applied direct to the first pair of deflecting plates, as shown. Owing to the distance separating the first pair of deflecting plates from the second it is necessary to introduce a definite phase-difference in the voltages applied to the second pair of plates, in order to ensure that the stream follows the required circular track. Accordingly. the upper pair of plates are fed from the lower through a Lecher-wire coupling, fitted with a 'trombone' section for fine adjustment.
The speed at which the cathode ray traverses the annular strip is, of course, determined by the frequency of the oscillations from the source O; whilst the multiplied frequency fed to the aerial depends upon the number of pairs of 'targets' - inset in the annular strip. Using eight targets, as shown the frequency taken out of the tube is four times that fed into it from the source O.
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