Patent GB-647126-A (GB)
Title: Combined radar and signal transmission systems
IPC: G01S7/00
Filed: 1946-10-18
Abstract: 647,126. Radiolocation; frequency modulation. WESTERN ELECTRIC CO., Inc. Oct. 18, 1946, No. 31075. Convention date, Oct. 25, 1945. [Classes 40 (v) and 40 (vii)] In a pulse radar system means are provided for frequency-modulating the carrier frequency of the exploring pulses with communication signals, and for separating communicationsignal information from received frequencymodulated pulse signals transmitted from similar radar systems. The output of pulse generator T, which may be a magnetron oscillator, is frequency-modulated at FM by signals from circuit S and is transmitted from aerial A. Received signals are directed by the T-R switch DU to frequency-changer D1, and thence through intermediate-frequency stages IFA, second detector D2 and video amplifier VA to a cathode-ray-tube range indicator I. The receiver also incorporates automaticfrequency control, the second detector which includes a frequency discriminator of the type described in Specification 489,094 supplying an A.F.C. voltage to the circuit AFC which controls the frequency of the local oscillator BO to maintain the intermediate frequency substantially constant. The apparatus also comprises a gating-pulse generator GPG, synchronized by the generator T, which gates the amplifier VA so that selected echo signals may be displayed alone on the indicator I. For receiving frequency-modulated signals from co-operating radar systems, a frequency discriminator FMD fed with intermediate-frequency signals and including a low-pass filter for rejecting the pulse-recurrence frequency is provided. All co-operating radar systems employ the same pulse-recurrence frequency and hence the discriminator FMD may be gated with pulses from the circuit GPG adjusted by means of a variable-delay circuit VDC to select the desired signals and to reject noise occurring in the intervals between received pulses. In an alternative-arrangement, Fig. 8 (not shown), the communication signals are extracted from the output of circuit AFC which is connected through a filter to head-phones. The apparatus is otherwise the same apart from the omission of units FMD and VDC. Frequency-modulation arrangements. Frequency-modulation is effected by varying the output impedance of the generator in accordance with the communication signals by means of the circuit FM. In the arrangement shown in Fig. 2, this is done by varying the position of a thin metal diaphragm 1 in one wall of the output wave-guide of the generator T by means of a telegraph-keying arrangement 2. Fig. 3 (not shown) shows a similar arrangement wherein the position of the diaphragm is varied electromagnetically by means of voice signals derived from a microphone. In the arrangement of Fig. 4 (not shown), voice signals control the position of a dielectric strip supported within the guide. Fig. 5 shows a coaxial-line output for the transmitter T, the output impedance being raised by means of a telegraph key 11 controlling a plunger 10 mounted within a branch arm. Fig. 6 (not shown) illustrates a similar arrangement employing voice-signal control. Figs. 7A, 7B (not shown) illustrate an output circuit comprising a wave-guide having a branch arm across which is connected a triode valve to the grid of which the communication signals are applied.