719,771. Automatic exchange equipment. BRITISH ELECTRICITY AUTHORITY, and MAXWELL, E. W. April 18, 1951, [Jan. 18, 1950], No. 1327/50. Class 40 (4). [Also in Group XL (c)] A communication system has means for enabling a subscriber on a land line to be automatically connected through junction equipment to a person at the remote end of a single channel radio link and voice-operated change-over means to operate the transmit-receive switch at the junction equipment. In the embodiment described, the exchange equipment PAX is connected to the junction equipment J, which controls the local transmitter TX and receiver RC of the radio link, over the line 1. The junction equipment comprises the line and radio voice-operated relay circuits LVOR, RVOR, respectively, supplied from the transformer T3 across line 1 and from the grid of the output valve 14 of the receiver RC, respectively. The T-R switch changes the H.T. supply from receiver to transmitter at the contacts tr1, tr2 of a relay TR/2 when the latter is energized by closing the contact b2 of a relay B/2 operated by circuit LVOR. A short-time delay unit ST suppresses the voltage pulse when the H.T. is switched from transmitter TX to receiver RC. A long-time delay unit LT clears the junction equipment after a predetermined period if a line extension called by the remote radio station does not answer. The circuit L is provided to transmit dialling impulses from the remote station to the line 1 while suppressing the modulating tone. When the line subscriber is connected by dialling to the radio outlet final selector F/S, relays LR/3, LRB/2 operate to reverse the line polarity of the radio extension at contacts lrb1, lrb2 and connect the caller to line 1 at contact ls1 operated by relay LS/1 energized by contact lr1, relay LR/3 being locked in by contact lr2. Ringing tone is then fed to the radio transmitter TX through transformer T1 and valve V1 and to the LVOR circuit to operate relay B/2. Contacts bl thereupon close to short-circuit RVOR and a voltage at point 8 in LVOR biases back the input valve V3 of RVOR. Closure of contacts b2 energizes relay TR/2 to switch the H.T. supply from receiver RC to transmitter TX. Between each cycle of ringing tone release of relay B/2 causes reversion of the radio equipment to the receive condition but the receiver output transformer T4 remains short-circuited for a short period by contacts td2 of relay TD/2 in circuit ST. Contacts bl remain closed longer but not long enough to prevent operation of circuit RVOR by the answering remote radio station. The latter answers by depressing a call key, Fig. 3 (not shown), which transmits a tone which is fed to RVOR, operates relay A/3, and causes a voltage at point 10 to bias back the input valve V2 of LVOR. Operation of relay A/3 operates relay AR/3 which locks over contacts arl and connects polarized relay p/1 across the line through contacts ar2. Contacts PI are thereby closed to energize relay PR/3, which closes contacts pr1 to maintain relay P /1 energized and opens contacts pr2 to release relay AR/3. The short energization of relay AR/3 is not sufficient to operate relay MR/1 in unit LT through contacts ar3. The RVOR relay A/3 also closes contacts A2 so that the receiver RC is connected to the circuit L. However contacts pr3 open almost immediately to prevent relay D/2 from impulsing the line once connection has been established. These conditions persist until there is a pause of duration greater than the decay period of the voltage developed across condenser 24 in RVOR. When the remote radio station calls a line subscriber, the call key switches the radio to the transmit condition and modulates the carrier with a tone which is thereafter pulsed by the dial interrupter. The received tone produces a voltage at the grid of valve 14 of receiver RC which is fed to RVOR, LVOR being disabled by a voltage appearing at point 10. The relay A/3 operates to connect the receiver output to the line at contacts a3. Contacts al energize relay AR/3 which locks at contacts arl and contacts ar2 close the circuit of polarized relay P/l. The latter, however, remains unoperated since the contacts lrbl, lrb2 are in the position shown, the line polarity being the reverse of that necessary to operate the relay. Relay PR/3 is not therefore operated. Circuit L is thus fed with the dialling impulses which operate relay D/2 to close contacts dl which energizes slow-torelease relay S/3. The latter prepares a circuit at contacts sl for contacts d2 to pulse the line 1 to operate the exchange equipment PAX. Relay S/3 also open contacts s2, s3 to disconnect during dialling the transformer T1 from the line 1 and the output of receiver RC. Relay AR/3 also closes contacts ar3 to energize the unit LT which slowly builds up voltage across relay MR/1 which cannot operate until the dialling period has expired. When dialling ceases, relays D/2, S/3 release but not AR/2, which maintains the line in the looped condition, while RVOR is deenergized removing the bias applied to LVOR. Ringing tone on line 1 then energizes the latter to operate relay B/2 closing contacts b2 to energize relay TR/2 and switch the radio equipment to transmit, while contacts bl short-circuit RVOR. The remote operator thus hears ringing tone. When the called subscriber answers the x contacts close to energize relay LRB/2 which reverses the line polarity and operates relay P/l. The latter energizes relay PR/3 through contacts p1 so that circuit L is disabled at contacts pr3 and unit LT is disabled by the opening of contacts ar3, relay AR/3 being de-energized at contacts pr2. Relay PR/3 also maintains relay P/1 through contacts prl. A two-way simplex conversation is now possible with automatic T-R switching by RVOR, LVOR. If the line subscriber does not answer relay MR/3 ultimately operates to open contacts mrl, de-energizing relay AR/3 to remove the loop from the line at contacts ar2.