Patent GB-1426168-A (GB)
Title: Swept receivers
IPC: H03J7/32
Filed: 1972-05-04
Abstract: 1426168 Cathode-ray tube displays PLESSEY CO Ltd 2 May 1973 [4 May 1972] 20868/72 Heading H4T [Also in Division G1] A swept receiver providing a panoramic display of signals, or serving as a spectrum analyser, is combined with means producing frequency marker (calibation) signals which are swept at the same rate as the receiver output signals and the marker signals being displayed on a cathode-ray tube (CRT). As shown in Fig. 2, the output signals in the band 50-60 MHz from the RF section 17 of the receiver are fed to a mixer 10 to which is also fed the output of a voltage controlled oscillator 8 swept over the range 150À7-160À7 MHz under the control of a sweep generator 9, the output of the mixer being fed to a band-pass filter 11 having a centre frequency of 100À7 MHz to provide the intermediate frequency (I.F.) for the main receiver 12 which supplies a rectified output for Y deflection of the beam 13 of the CRT display tube against an X-time base provided by a staircase generator 22. For the production of the frequency marker signals a spectrum generator or synthesiser produces a 50 MHz or 60 MHz sweep limit marker output on line " a " and a succession of signals spaced by 10kHz in the 50 MHz to 60 MHz range on line " b ", the latter signals being selected via switch 14a during the sweep portions of oscillator 8 and processed in mixer 15, I.F. filter 16 and auxiliary recesses means 17 (similarly to the operation of the elements 10, 11 and 12) to provide signals for the Y-deflection of beam 18 of the display CRT. The output signals from the receivers 12 and 17 are also applied to a computer or digital measuring system 19 including gating means which operates to produce output signals when there is correspondence between predetermined frequency markers and received signals so that the presence of a signal or signals at a particular frequency or frequencies is detected. In order to ensure that, at the start of each sweep, the frequency of the swept oscillator 8 is at the correct value, the switches 14a, 21a and 21b are operated during the periods between sweeps, switch 14a supplying the 50 MHz signal to mixer 15 and switch 21b supplying the I.F. output of filter 16 to a comparator 21 which also receives the 100À7 MHz output of a calibration oscillator 20. If the swpt oscillator 8 is not at the correct start frequency, e.g. 150À7 MHz, the output of I.F. filter 16f, 16a will not have the correct value of 100À7 MHz and comparator 21 will then produce an output which is employed to adjust oscillator 8 to the correct frequency (100À7 MHz). The staircase generator 22 (which provides the X-deflection) may be controlled by the output signals of the receiver 17 or by maens of a pulse generator 23 depending on the position of switch 17a and a counter 24 provides a beam blanking output to the Z input of the CRT after a predetermined number of counts The output of the pulse generator 23 may be supplied to a logic circuit 25 which provides signals for application to the Y input of the tube to produce a required " back-up " display and further such displays may be provided by other inputs as shown. The display may, alternatively, be provided by a split beam or a dual beam cathode-ray oscilloscope having its own X deflection means.