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Coaxial Equipment Line (CEL) Systems. |
In the days long before optical fibre cables were invented, there was a requirement to send telephone and television signals, en masse, between exchanges, sometimes over a long distance. The Coaxial Equipment Line (CEL) Systems were designed to transmit over type 375E coaxial cable. The equipment cards and modules fitted the 51-type equipment practice. Later designs followed the 62-type racking.
Richard Defries gives an overview of the equipment as once was used in a main exchange.
"I first entered into the depths of a Trunk Repeater Station (TRS) in 1967 where it was all a mystery with nothing going click and making lots of noise, but I was assured by those sleeping down there that it was the heart of all long distance telephony. At this time the latest co-axial analogue line systems were being installed to replace the earlier co-axial line systems that were used to support the valve driven AC8, which was used for long distance AC signalling before the advent of AC9 (both valve and transistor), which were to become the STD trunk network at that time."
"The line systems CEL 1006 and 1007 (recovered in 2000) carried either 960 ccts of 4 kHz bandwidth (speech being 300-3400 Hz) in the case of CEL 1006 or 3 x 960 ccts in the case of CEL 1007. In later life these line systems carried more and more data ccts and private wires, but towards the end of their working life were superseded by the digital network that we have today which allows for much higher data rates."
"CEL stands for Co-axial Equipment Line System followed by a 100X number where x is a number which was followed by a letter to indicate the equipment manufacturer. CEL 1007 was manufactured by STC as a 12 MHz line system which in fact muxed together 3 x 4 MHz lines into one 12 Mhz traffic path over one pair of co-ax cables. This involved a lot of refurbishment at the time of installation as all of the joints in on the co-ax route had to be checked and remade if they failed the testing spec, as the older 4 MHz line systems used a lower spec. The line system used either buried amplifiers (repeaters) housed in Cable Repeater Equipments (CRE) sited in joint boxes spaced at 2 km in small UAX type of surface amplifiers mounted in 62 Type racks or in convenient surface repeaters in telephone exchanges along the route. As our TRS was a terminal station we only had 5 times, 4 MHz line systems and one times, 12 MHz line system whereas exchanges outside our locality had many more through systems as they were both on main routes into and out of London."
"The other equipment required was Channel, Group and SuperGroup equipment which generated the carrier frequencies along with the Master Oscillator Rack which tried to keep it all in synchronisation. In order to achieve the 4 MHz of the line system multiplexing techniques were employed for mux up/down from the basic group of 12 channels to give 48 kHz muxed up/down x 5 to give Group muxed up/down x 16 to give a SuperGroup or one 4 MHz line system which could then be x 3 to give 12 MHz line system which was the CEL 1007. 4 MHz line systems as far as I know only ever had CRE sited amplifiers. Both of these CELs employed at the time state of the art transistor technology which was very advanced for the time. Both used a level of Automatic Gain Control (AGC) which allowed self regulation over 0+ or -3dB which took account of current fluctuations due to temperature over the course of the year."
"Each of the equipments had a different EFT or Equipment Frequency Translation number and in our TRS we still had some EFT 80 which dated from the mid to late 1950s which was still carrying traffic up until 1990."
Valve Systems
CEL Nos. 1, 1A, 2, 2A, 2B all were suitable for type 375E coaxial cable with: Introduced circa 1945. A working bandwidth of 60 Hz to 2540 kHz. For the transmission of 10 telephony supergroups (600 circuits). A repeater spacing of 6 miles.
CEL No.3 For the transmission of 3 MHz TV signals. Line frequency range 3 MHz to 7 MHz.
CEL No.4 Introduced in 1951. For the transmission of 3 MHz TV signals. Line frequency range 60 kHz to 4340 kHz.
CEL No. 4A Improved version of CEL No.4 Introduced circa 1957. Also suitable for transmission of 17 telephony supergroups (1020 circuits). Line frequency range 60 kHz to 4340 kHz. 375E type cables
CEL No. 5 Simplified version of CEL No.4 for use on short TV links.
CEL No. 6A Introduced circa 1955. The first not of Post Office design to be deployed on a large scale. Derived from a Standard Telephones & Cables (STC) system. Type 51 equipment racks. For the transmission of 16 telephony supergroups (960 circuits) or a 405 - line TV signal. Line frequency range 60 kHz to 4092 kHz.
CEL No. 8A First used on the London - Oxford - Birmingham route, cable no.5 using 3 mile repeater spacings. Introduced 1958. Designed by STC. Type 51 equipment racks. For the transmission of 45 telephony supergroups (2700 circuits) or 1200 circuits together with a 625 - line TV signal. Line frequency range 0.3 MHz to 12.5 MHz.
CEL No.10A
CEL No.11A, 11B
CEL No.13A
CEL No.14A
CEL No.18A
Transistorised Systems
CEL 1000 For the transmission of 5 telephony supergroups (300 circuits). Line frequency range 60 Hz to 1300 kHz. Type 174 cable, maximum of 60 miles.
CEL 1006 Introduced circa 1971/2. For the transmission of 16 telephony supergroups (960 circuits). Line frequency range 60 Hz to 4028 kHz. 4 MHz bandwidth. Type 174 or 375 cable.
CEL 1007 Introduced cira 1971/2. For the transmission of 45 telephony supergroups (2700 circuits). Line frequency range 312 kHz to 12,388 kHz. 12 MHz bandwidth. Type 375 cable.
CEL 4000 Introduced circa 1971. Type 62 equipment racks. For the transmission of 45 telephony supergroups (2700 circuits). Line frequency range 312 kHz to 12,388 kHz. 12 MHz bandwidth. Type 174 or 375 cable.
60 MHz FDM (Frequency Division Multiplexing) Systems
London - Birmingham - Manchester First trialled January 1973. 18 - tube coaxial pair cable.
8.448 Mbit/s Digital Line Systems
References
Thanks to Richard Defries (Y2K notes)
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