Patent GB-183203-A (GB)
Title: Improved method for preventing disturbing induction between adjacent leads carrying approximately the same high frequency waves
IPC: H04J1/12
Filed: 1921-04-12
Abstract: 183,203. Gill, H. A., (Deutsche Telephonwerke Ges.). April 12, 1921. Induction, preventing; repeating systems.- Relates to means for preventing disturbing inductive action between adjacent telegraph or telephone lines carrying signalling waves of the same or approximately the same frequencies. According to one method, one or more of the pairs of conductors are divided into sections, the frequency of the carrier wave being varied from section to section, whilst in a second method the same or apprcximately the same carrier frequencies are onlv used for the same directions of speech transmission. The lines AB, CD, Fig. 1, represent two adjacent pairs of conductors both arranged for transmission in two directions, signalling in the directions A to B, B to A, C to D, and D to C, being effected by carrier waves of frequencies #3, #4, #1 and #2 respectively. If the two frequencies in each direction of speech transmission, namely, #3, #1 and #4, #2 are the same or approximately the same, normally considerable inductive interference is present between the two pairs of lines, but according to the invention this is reduced by dividing the pair of lines AB into sections of the order of 100 kilometres, and causing the carrier frequency in both directions to alternate from #3 to #4, or vice versa, from section to section. In this manner inductive disturbance between the frequencies #3 and #1 is only present over 4/7 ths of the total line length and that between the frequencies #4 and #2 only over 3/7 ths of the line. A twoway frequency transforming stage T, Fig. 1, adapted to transform a carrier frequency from #3 to #4 is illustrated in greater detail in Fig. 3. Waves of frequency A3 coming from the left are received by a receiver E which causes a relay R to operate a transmitter S1, to relay the signals at a different carrier frequency #4. Similarly. the receiver E1, relay R1, and transmitter S. change the frequency of carrier waves coming from the right from #3 to #4. The relays R, R1 may be made slightly sluggish in action. Microphones or tuned circuits coupled by transformers may be used in place of the coupling relays R, R,. The pair of lines CD may also be divided into sections in the same manner as the lines AB, and the carrier wave may, if desired, be transformed from section to section according to three or more frequencies instead of two as indicated in Fig. 1. The known method of mechanical crossing of the wires may be used on one or both pairs of lines in addition to the abovedescribed arrangement. The invention is stated to be applicable also to multiplex working. In this case the carrier frequencies of the different messages over one pair of lines are interchanged from section to section, those of the other pair of lines being similarly interchanged but in the reverse sense, so that no two carrier waves of the same frequency pass along adjacent sections of the two pairs of lines in the same direction. If desired, only half the messages may have their carrier frequencies changed at each frequency transformation stage.