Patent GB-1087870-A (GB)
Title: Improved ionosphere radio sounding system
IPC: G01S13/02
Filed: 1966-01-14
Abstract: 1,087,870. Testing radio-frequency systems. GRANGER ASSOCIATES. Jan. 14, 1966 [Jan. 25, 1965], No. 1843/66. Heading H4L. In a sounding system for ascertaining the propagation properties of a radio path, a transmitter is periodically stepped over a band of frequencies and sends out a pair of pulses at each step (Fig. 3, not shown) to a co-operating receiver, which has means for representing the received peak amplitudes corresponding to the various frequencies in digital form (Fig. 4, not shown). The received signals are processed by a demodulator 11 followed by an amplifier 12 connected to two paralleled circuits each comprising a gate 15 or 17 and a storage device 16 or 18, the gates being opened alternately to accept successive second pulses received from the transmitter. The storage devices are connected to an analogue switch 20 which passes on the stored signal having the higher amplitude. In this way, as frequency stepping progresses, each signal is compared with the signal received immediately before, and the greater of the two is chosen. A connection (not shown) is taken from each storage device 16, 18 to a pulse correlation output lead 9, whereby any signal is rejected unless both pulses of the relevant frequency step have been received. The signal from the switch 20 is digitized by conventional means comprising pulse and ramp generators 22, 23 and a comparator 21, whose output is taken through a binary counter 40, a binary to decimal converter 42, a decimal to printing telegraph code converter 43, and a character generator 44 to a -printing telegraph machine 45. A gate 41 is interposed between the counter 40 and the converter 42. The input is also processed by a second demodulator 26 connected to a gate 27 which is opened at each step for a short period before the first pulse is sent so that noise signals only are passed to an integrator 28, which establishes a noise signal level. A Schmitt trigger 60 is connected to the ouput of the amplifier 12 via an attenuator 61 ;and is controlled by means of a connection to the output of the integrator 28, so that signal pulses acceptably above a predetermined noise level are repeated on the lead 9 and operate a flip-flop 47, connected to a counter 48. If the counter 48 does not receive two pulses at any step the gate 41 fails to open and the printing telegraph machine 45 produces a blank instead of a digit on the record (Fig. 4, not shown). A multipath detector 30 is also provided, in which the output of the amplifier 12 is taken to a Schmitt trigger 36 via a pulse stretcher 29 (for compensating for any breaks in a received pulse), said trigger being controlled by voltages from peak detectors 31, 34 connected respectively to the signal and noise outputs. A ramp generator 37 is controlled by the output of the Schmitt trigger 36 and its output is taken through another Schmitt trigger 38 which is controlled by a reference standard 39. In consequence, a signal is only produced upon a lead 10 if the duration of the received pulse is increased because of multipath distortion. The lead 10 is connected to one input of an " AND " gate 49, the other input of the said gate being connected through a flip-flop 50 to the lead 9. If a signal is received through the flip-flop, indicating that both pulses of a frequency step are acceptable, and if a signal is also received on the lead 10, indicating that there is multipath distortion, an output results which is taken via a storage device 51 to the decimal to printing telegraph code converter 43, whereby an underline to the amplitude digit is printed (Fig. 4, not shown). Additional components 52, 53, 54 may be provided for data logging.