Patent GB-931104-A (GB)
Title: Radio interrogator-responder devices
IPC: B61L25/04
Filed: 1962-01-29
Abstract: 931,104. Transponder apparatus; inductive signalling. SIEMENS & HALSKE A. G. Jan. 29, 1962 [Jan. 27, 1961], No. 3346/62. Class 40 (5). [Also in Group XXX] Relates to interrogator-responder apparatus providing coded information relating, for example, to railway vehicles, by means of inductive coupling between transmitting and receiving coils wherein single sideband plus carrier interrogating and single side-band responding signals are used, the same carrier frequency being used in each case but being arranged so that the respective side-bands do not overlap. In the arrangement described, the information is transmitted as seven digit decimal numbers, the individual digit positions being successively interrogated by frequencies f1 to f7 and the values 0 to 9 possible in each digit position being represented by transmitting two out of five response frequencies #<SP>11</SP> to #<SP>15</SP>, these latter frequencies being obtained by frequency division of the carrier #<SP>0</SP> = 115kc/s. The interrogating signals are sent by means of carrier and upper sideband, the lower sideband being used for response signals. At the interrogator, Fig. 2, the carrier #<SP>0</SP> is generated by a crystal oscillator 1 and is modulated at 3 by a wobbulator 2 providing a frequency sweep of 7.5 to 15 kc/s., which comprises the band occupied by the frequencies #<SP>1</SP> to #<SP>7</SP>. A filter 4 selects the upper side-band, which after amplification at 5 is combined at 7 with unmodulated carrier supplied via an amplifier 6, the combined signal being supplied to a transmitting coil 8. The carrier #<SP>0</SP> and upper side-band are picked up by the series connected resonant circuits 11 and 12 respectively at the responder, Fig. 3, and demodulated at 13, frequencies #<SP>1</SP> to #<SP>7</SP> being selected by filters 17, rectified at 18, and via a coding device 19 energizing selected oscillators 20 supplying the respective pairs of frequencies #<SP>11</SP> to #<SP>15</SP> for each digit appropriate to that responder. The received carrier #<SP>0</SP> is supplied via line 21 to synchronize the oscillators 20 and is also supplied to a modulator 22 together with the response frequencies. A filter 23 supplies the lower side-band via an amplifier 15 energized by the rectified carrier voltage, to a transmitting coil 16 arranged perpendicularly to coils 11, 12 to avoid mutual interference. The response signal is picked up by a coil 31, Fig. 2, and heterodyned at 33 with the carrier #<SP>0</SP> from oscillator 1. The resulting frequencies #<SP>11</SP> to #<SP>15</SP> are supplied via filter 34 to a variable gain amplifier 35 and separated by filters 36 to generate two signals per digit position at the output of rectifiers 37 (only two shown). These signals are supplied via a supervisory device 38 which checks that two rectifiers provide a signal at each digit position to an evaluating device 39 which is also supplied by the wobbulator 2, filters 42 and rectifiers 41 with signals corresponding to the frequencies #<SP>1</SP> to #<SP>7</SP>. The output signals of the rectifiers 37 also control a device 40 which controls the gain of the amplifier 35 to maintain constant the level of the signals supplied to the evaluating device 39. The responder may be provided with its own power source, and using the two out of five code may have two oscillators instead of five, the oscillator frequencies being changed as required. At the interrogator receiver, instead of the conversion to frequencies #<SP>11</SP> to #<SP>15</SP> at 33 by the use of the carrier #<SP>0</SP> a lower frequency lying within the received side-band may be generated at 43. The filters 36 are designed to take the new frequencies thus derived and may be of reduced bandwidth, thus reducing the effect of interference. With fast-moving devices a number of interrogating devices may be disposed one behind the other in the direction of movement, for example, one for each digit.