Patent GB-839288-A (GB)
Title: Improvements in or relating to party line telecommunication systems
IPC: H04Q5/00
Filed: 1958-07-14
Abstract: 839,288. Party line systems. TELEFONAKTIEBOLOGET L.M. ERICSSON. July 14, 1958 [July 12, 1957], No. 22565/58. Class 40 (4). [Also in Group XL (c)] In a party-line system each substation is equipped with a v.f. sender, and also a filter connected to a v.f. receiver. The filter is arranged to be adjustable so that if a frequency corresponding to the substation's tens digit is received, the filter is then reset to accept frequencies corresponding to its units digit. If at any time a frequency is received corresponding to a tens or units digit not appropriate to the substation's number, the substation is disconnected from the line. First embodiment.-In the subscriber's equipment I relay r49 operates to the calling subscriber's loop and r36 follows to bring up the first relay r371, in a chain of such relays, which corresponds to a free line. Relay r214 in the line equipment GA then operates to the line loop over rectifier L41 in the subscriber's equipment I. Relay r213 follows to reverse the polarity emitted by equipment GA to the line as a signal that the line is being taken into use. Relay r213 brings up r39 to prevent further use of the chain and r36 releases. Relay r49 brings up r410 which changes the polarity to the subset whereby L52 is back-biased to disable the microphone M. If the control equipment GE is free r214 brings up r291 and r27 follows to busy the equipment GE and connect up dial tone. Relay r291 also brings up r211, followed by r212 which releases r213, r214, the original polarity on the wires outgoing from GA being restored. This change of polarity has meanwhile operated r31 in all substation blocking circuits LB associated with the line and r33 follows to bring up r371 in the remaining substation selector circuits LV. Relay r39 follows to bring up r412 which disconnects these subscribers from their equipments I. When the polarity reversal ceases r31 releases, r32 comes up and r33 releases. The receipt of dial tone in all subscriber's equipments beings up r41 and r47, and r44 follows to connect up the filter FTE. These filters are set to accept a frequency indicative of the tens digit of the subscriber concerned. The calling subscriber now operates his sender to transmit the wanted tens digit, and in the corresponding subscribers' equipments the tone is accepted by the filters FTE and relay r42 consequently operated. The tone is also accepted in control equipment GE by filter TE to operate r21 and r23 follows to disconnect dial tone. Relay r21 is thereupon released and r24 operated. In the subscribers' equipments r42 brings up r45; r41 and r42 release, and r46 and r43 operate the latter changing over the filters FTE to accept the appropriate units frequencies. At substations where r42 is not operated r41 releases at the end of the signal, and r47 follows, whereupon r46, r35 operate to release r371 which disconnects these subscribers from the line. Relay r35, operated, however still prevents these subscribers having access to the line afresh. When the calling subscriber transmits the units frequency, r21 operates in control circuit GE, r23 releases to bring up r25, r22 and release r21, r24. Relay r22 resets the filter TE to be receptive to ringing tone. At the wanted substation the units tone brings up r42 and r411 follows to release r412 which reconnects the subset to the equipment I and a burst of ringing current is sent from source RG and corresponding ringing tone is reverted from source Su2. At all substations on the line r41 operated by the units tone releases r47, r44, the latter at the called substation replacing the existing ringing and tone sources by intermittent sources RGi, Su3. At unwanted sub-. stations release of r47 brings up r35 which releases r371 to disconnect these substations from the line, r35 however busying the line against seizure by these substations. At the wanted substation release of r47 releases r410 to restore the original polarity to the subset to bring in the microphone M. In control circuit GE reception of ringing tone operates r21, r210 and chain relay r291 and r27 are released whereupon the control circuit is released. When the called subscriber (assumed free) replies his loop current releases r411 by differential action, thus completing a feed circuit over windings of r49 which operates. With both subscribers now connected conversation proceeds the A.C. signalling circuits being disconnected from the line by r46 and r44 in each of the substation equipments I. If the called subscriber was already engaged then one of chain relays r371 ... n and r39 being already operated he could not, during the attempted setting up of this call, be connected to the line outgoing from GA. Consequently r21 fails to operate since no ringing tone is reverted from the called subscriber's equipment I so that r210 fails to operate and r291, r27 fail to release. When r22 completes its slow release (due to deenergization by r24) it connects up busy tone from source Su1. Ultimately r26 (also deenergized by r24) completes its slow release whereupon r210 operates to release r291, r27, r25 and r26 re-operates and GE is thus restored. When the calling subscriber hangs up feed relay r49 releases, followed by r214, r212. Relay r213 operates momentarily to send a polarity reversal to operate r31 which causes a momentary operation of r34 and r35 which release the chain relays r371, r39, the latter releasing r46 and r43 so that all circuits are now at normal. Disconnection after a completed call takes place as described above when both subscribers have hung up. Second embodiment.-All signals are v.f. so that the lines may be radio links if necessary. The calling subscriber's loop brings up r99, followed by r94 and r71 the latter seizing a free line by operating chain relay r811 in which circuit r82 also operates to release r71. Relay r94 operates r85 and r87 follows to disconnect the line from the subset and also the tone amplifier SF82. Relay r910 then changes the polarity to the subset to disable the microphone and connects tone source Su2 to line as a calling signal. In all the substation equipments LBT filter T7 passes this calling signal to operate relay r72 and r74, r76 follow, the former preventing any other subscriber from initiating a call over this line. In the control circuit GET the signal is passed by filter T6 to operate r611 and when the control circuit is free chain relay r681 operates in series with r67 to cause r64, r65 to interact whereby a burst of reply tone is passed to line from generator O. In the calling subscriber's equipment this tone is accepted by filter T8 to operate r84 which disconnects the calling signal Su2. This tone is however restored after a brief pause by the release of r85 and r84. Relay r87 also releases to reconnect the calling subset to the line so that tone from Su2 is now received as a " dial tone ". The brief interruption in tone causes r72 to bring up r75 in all the subscribers' equipments and relays r811 follow to connect all free subscribers to the line, relays r82 also coming up, followed by r912 which disconnects the subsets (except in the calling substation) and conditions the filters T8 to accept tones indicative of their individual tens digits. In all equipments r88 operates to receipt of the dial tone and r98, r95 follow. In the calling subscriber's equipment r912 is not up and filter T8 in these conditions will accept any of the digit tones, so that when the tens digit is sent r84 is operated as well as r88. Relay r96 then disconnects the dial tone. Relays r98, r97 also operate. When the dial tone ceases r72, r74 and r76 in all relay sets LBT release and r77 operates. When the calling subscriber sends a tone indicative of the tens digit this signal passes to the outlet I of filter T6 to operate r63 in the control circuit GET. Relay r63 operates r62, and r63 releases to bring up r61. At the free substations if the tens digit is appropriate the filters T8 pass the tone to bring up r84. Relay r88 is also operated by the tone. Relay r96 makes a permanent registration of the receipt of the tone and r88, r84 release the former bringing up r97, whereupon r86 operates to reset the filter units T8 to accept the relevant units tone. In substations not having the appropriate tens digit only r88 operates to the tone, whereupon r97 and r73 come up, the latter releasing r811, r82, r97, r98, r912 and r95, the first disconnecting the substation equipment from the line. Relay r73 however busies the line to that substation. When the calling subscriber sends out the units tone, relays r63, r62 and r610 operate in the control circuit GET whereupon r67, r681, r65, r61 release so that the equipment is restored and disconnected from the line. At the calling substation equipment r84, r88 operate to release r98, r95, r910, the latter restoring the original polarity to energize the subscriber's microphone. At the remaining unwanted circuits r88 operates r73, whereupon r811 and r82 release the equipment from the line as previously described. At the wanted substation r84, r88 operate r911 and r912 releases to connect up the subscriber's instrument. Ringing current from source RG is sent over the loop and ringing tone is reverted from Su4. Relay r88 releases r98 and r95 follows to replace the sources of ringing current and tone by intermittent ones. When the called subscriber answers, his loop current releases r911 by differential action and disconnects the ringing current and tone. Relays r99, r94 operate and conversation proceeds. Each substation has a normally operated relay r91 which may release if the call is not set up within a specified time. This operates r93 which reverts a disconnection tone from Su5. In both calling and called subscribers' equipment this tone brings up r72 which brings up r78, r76 and releases r75, r77. During the release time of r75, r811 is released but r82 stays up. At the called subst