Patent GB-869566-A (GB)
Title: Improvements in and relating to telegraph system
Inventor: DUUREN HENDRIK CORNELIS ANTHON
IPC: H03M13/51
Filed: 1957-10-15
Abstract: 869,566. Multiflex radio signalling. STAAT DER NEDERLANDEN TEN DEZE VERTEGENWOORDIGD DOOR DE DIRECTEUR-GENERAAL DER POSTERIJEN, TELEGRAFIE EN TELEFONIE. Oct. 15, 1957 [Oct. 20, 1956], No. 32174/57. Class 40(5) In a telegraphic system in which signal elements are transmitted as electric oscillations at frequencies lying within predetermined bands of frequencies, means are provided to prevent the transmission of two successive signal elements lying in the same band of frequencies and to transmit, instead, the first of said signal elements followed by an auxiliary signal element at a frequency lying in an auxiliary band of frequencies. In a two channel system each channel may comprise traffic from one subscriber or from a number of subscribers combined by time division multiplexing. As shown in Fig. 1, frequencies f 1 , f 2 , f 3  and f 4  are used to transmit the four possible combinations of mark and space elements in channel I and channel II, a mark being denoted by a black circle and a space by a blank circle. The frequencies f 1 , f 2 , together form a sub-channel a and the frequencies f 3 , f 4 , constitute a second sub-channel b, and for each subchannel there is a selective receiver at the receiving end. To avoid the occurrence of mistakes due to element prolongation when two frequencies reach the same receiver one immediately after the other, if, for example, element combination 2 (f 3 ) is followed by element combination 3 (f 4 ) the frequency f 3  is followed by a frequency f 6  of an auxiliary sub-channel c comprising frequencies f 5 , f 6  as shown in Fig. 2, a third selective receiver being provided for this subchannel. Similarly element combination 1 (f 1 ) followed by element combination 4 (normally f 2 ) is transmitted as f 1 , f 6 , and so on. In this way, for channel I frequencies f 5  and f 6  represent respectively a marking element and a spacing element and for channel II frequency f 5  or frequency f 6  represents a marking element if it is preceded by a frequency of sub-channel a and a spacing element if it is preceded by a frequency of sub-channel b, as shown in Fig. 2. A similar arrangement is described for three channels in which the eight possible combinations of mark and space are represented by frequencies f 1  to f 8  which are transmitted in two sub-channels comprising respectively f 1  to f 4  and f 5  to f 8 , and the auxiliary channel comprises frequencies f 9  to f 12 . Alternatively in a three channel system, the frequencies f 1  to f 8  may be divided between four sub-channels, in which case only two frequencies f 9 , f 10 , are required for the auxiliary channel. A transmitter for the arrangement indicated in Figs. 1 and 2 comprises five generators a to e Fig. 8a, which deliver five frequencies f a  to f e . Switches S1 and S2 are actuated simultaneously, switch S1 being actuated by channel I and switch S2 by channel II. If there is a marking element in channel I the switch S1 will be in position 1 and for a spacing element it will be in position 2. In channel II for a marking element switch S2 normally will be in position 1 and for a spacing element normally will be in position 2. If, however, there are two marking elements in succession in channel II, switch S2 will be in position 1 during the first marking element, and in position 3 during the second marking element. Similarly, if there are two spacing elements in succession in channel II, switch S2 will be in position 2 during the first spacing element and in position 3 during the second spacing element. The two frequencies from the switches S1, S2, are connected to a modulator controlling a transmitter and the frequencies delivered by the modulator are as follows. If f a  and f c  occur simultaneously a frequency f c -f a =f 1  is supplied to the transmitter. If fb and f c  occur simultaneously the resultant frequency is f 2 . If f a  and fd occur simultaneously the resultant frequency is f 3 . If f b  and f d  occur simultaneously the resultant is f 4 . If f a  and f b  occur simultaneously the resultant is f 5 , and if f b  and f e  occur simultaneously the resultant is f 6 . The switch S2 is shown in Fig. 9, the generators, c, d, e corresponding to the generators c, d, e of Fig. 8. Valves B1, B2, B3, constitute a trigger circuit wherein if one of the valves becomes conductive the remainder are non-conductive. If B1 is conductive the normally blocked rectifiers 1, 2, conduct due to the voltage drop across resistor R1, and a voltage of frequency f c  is supplied from generator C via transformers T1, T4, to the modulator. Similarly, if B2 is conductive the rectifiers 3, 4, conduct and a frequency f d  is fed from generator d via transformers T2, T4, to the modulator, and when B3 conducts, a frequency f e  is fed via transformers T3, T4, to the modulator. An impulse generator P1 delivers a positive impulse at fixed intervals and T is a trigger which receives at its input the signals from channel II. A marking element at the input to T causes its output terminal T1 to be at a positive potential and its output terminal T2 to be at a negative potential whereby diode G2 will conduct. A spacing element will cause the reverse to take place and diode G1 to conduct. If trigger T is in the marking condition, a positive impulse from P1 will be diverted via resistor R14 and diode G2 and will not be able to pass via R10 to the grid of B2 or via R12 to the grid of B3, but the impulse will pass via R 13 and R9 to the grid of valve B1 and B1 will conduct to apply a voltage of frequency f c  to the modulator. The impulse also will be applied via R13 and Rll to the grid of valve B3, but R11 and R12 form a potentiometer and the voltage will be less than that applied to B1 and valve B3 will not conduct. When the trigger T is in the spacing condition a positive impulse from P1 will be directed via R13 and G1 and the impulse cannot pass via R9 to the grid of valve Bl or via R11 to the grid of B3. The pulse will be applied via R14 and R10 to the grid of valve B2 which will conduct and a voltage of frequency f d  will be supplied to the modulator. The pulse applied to valve B3 via R14, R12 will be insufficient for valve B3 to conduct, as before. When the valve Bl is not conducting the diode G3 is blocked but when a marking element appears in channel II and valve B1 conducts, the diode G3 is unblocked and if the next signal element is a marking element the pulse from P1 will be diverted via G3, valve B3 will conduct instead of valve Bl, and a voltage of frequency f e  will pass to the modulator. Similarly, if two successive spacing elements appear in channel II, the diode G4 conducts and the impulse resulting from the second spacing element causes valve B3 to conduct instead of valve B2. If a third similar element follows, the resulting impulse then causes the corresponding valve B1 or B2 to conduct. At the receiver, Fig. 11, frequencies f 1  to f 6  arrive in an arbitrary sequence at terminal A, filter F1 passes frequencies f 1 , f 2 , filter F2 passes frequencies f 3 , f 4 , and filter F3 passes frequencies f 5 , f 6 . Each filter is followed by a limiter, Bl, B2 or B3 and a frequency discriminator D1, D2, or D3. The output terminal 7 of Dl is positive if frequency f 1  appears and negative if f 2  appears and the terminal 8 is positive if either f 1  or f 2  appears. Terminals 9 and 11 of discriminators D2 and D3 respectively are positive if f 3  or f 5  appears and negative if f 4  or f 6  appears, and terminals 10, 12, respectively are positive when any of the frequencies, i.e. f 3 , f 4 , f 5 , f 6  to which they are responsive appears. The output terminals 7, 9, 11, are connected respectively via diodes I to 6 to a trigger T1, controlled by an impulse generator P1, which provides the signal for channel I and if either one of terminals 7, 9 or 11, is positive this signifies a marking element. If either one of the terminals 7, 9, or 11 is negative, the trigger Tl assumes a position which provides a spacing element for channel I. The terminals 8 and 10 are connected to a trigger T2, also controlled by P1, which provides the channel II signals, and gives a marking signal when terminal 8 is positive and a spacing signal when terminal 10 is positive. If due to the occurrence of f 1  or f 2 , T2 is in the marking condition and immediately afterwards f 5  or f 6  occurs, bistable trigger 2 remains in the marking condition and the next pulse from P1 delivers a marking element to channel II. If due to the occurrence of f 3  or f 4 , T2 has assumed the spacing condition and f 5  or f 6  follows immediately, trigger T2 remains in the spacing condition and the next pulse from P1 delivers a spacing element to channel II. The potential on terminal 12 may be utilized to indicate to the receiver in channel II that f 5  or f 6  has arrived and that there is no question of prolongation of the preceding impulse. Specification 778,621 is referred to.