by Adrian Hilton
This system was the first 14 Mhz Analogue Submarine Cable System connecting Broadstairs on the South-East coast of the UK with Ostend in Belgium. The system was capable of carrying 1260 simultaneous telephone conversations (21 Supergroups) over a single Coaxial cable. The system used a single Coaxial Tube to carry the transmissions in both directions. The Lower Band (312Khz - 6 Mhz) carrying traffic from Broadstairs to Ostend and the Upper Band (7Mhz - 14 Mhz) brought the receive path back to the UK. DC Power was applied to the Centre Conductor of the Cable and this was used to supply the Undersea Amplifiers. Each Amplifier was equipped with a High-pass and Low-pass filter to separate the two directions of transmission and separate amplifiers, one for each direction of transmission, were held within each repeater housing. Pilot signals were inserted below the lowest frequency and above the highest frequency to allow monitoring of the system performance. Additional Supervisory signals were used below the Traffic and Pilot Signals to enable supervision of the Repeater Amplifier Circuits. These supervisory signals were transmitted in the low-band and circuits within the repeaters returned them in the high-band. Loop-backs could be initiated at each repeater so it was possible to established in which cable section a cable break had occurred.
Below is a photograph of the Terminal Equipment
In the photograph above:-
From right to left
The rack on the far right-hand side of the photo housed the "Supergroup Limiters". These cards at the top of the bay protected the system from any High Level signal causing an overload across the whole of the traffic path. Each individual Supergroup (60 Channels) was monitored before it was multiplexed into the Wideband and if an excessively high level signal was present on any of those Channels the whole 60 circuits band was compressed to ensure that it did not interfere with all the remaining traffic. An alarm was raised to indicate the affected Supergroup.
The lower section of the rack was the multiplexing equipment used to combine the 21 Supergroups into the 6 Mhz band for transmission to Ostend and demodulate the Receive signals returning from Belgium.
The second rack seen is the "Wideband Bay". This bay comprised of cards to equalises the levels of the Passband 300Khz - 6 Mhz of the Transmit path and 7 - 14 Mhz on the Receive Path. The two transmission paths were combined and fed across a single Coaxial Cable. Pilot Meters can be seen. These enabled the transmission performance to be monitored across the transmission bands. Adjustments were necessary to compensate for Sea Temperature changes. Adjustments could be made in 0.5 dB steps and this was sometimes necessary several times per week. The equaliser switches can be seen next to the Pilot Monitors. Pen recorders were also used to record the system performance over time. These can be seen in the lower part if the bay.
The third rack housed the communications shelf which enable the two terminals Broadstairs and Ostend to talk whilst making the necessary adjustments. A system "Noise Monitor" can be seen above the handset shelf.
The fourth rack was the Submerged Repeater Monitoring Equipment (SRME). This allowed the supervision of the performance of the Sea Bed Repeaters. Any deterioration of the amplifier circuits could be detected as could an any additional loss in the cable.
A frequency counter (using Nixie Tubes) can been seen. This was used to set the supervisory frequency for each individual repeater.
Below the frequency counter was a mechanically driven sweep oscillator. This enabled a weekly supervisory run to be performed to plot any deterioration within submerged plant.
To the left of the SRME bay is a duplication of a very similar rack layout but this time for the Broadstairs - Domburg System (UK-Netherlands 9)
posted on Friday, September 12, 2014 at 1:46 PM
by Adrian Hilton
by Adrian Hilton
This cable was landed at Joss Bay, Broadstairs on 6th July 1974. The shore end was floated ashore from the Cable Ship DG Bast using flotation buoys that were later cut free by a diving team
A section of the Beach was closed to the publish during the procedure which took a good part of the day
The General Manager (Canterbury) offered his apologises
A JCB was required, driving along shore, to provide sufficient power to pull the heavy cable ashore
Once ashore the cable was pulled into the duct and up the access slope where the armouring could be stripped back and clamped in the Beach Manhole
The cable was then stripped back and connected to the land cable section
Centre conductor brazing
Polythene was injected and moulded around the inner conductor
This was then X-rayed to ensure the joint is free from any voids or extraneous material.
Once confirmed to be good the outer copper tapes where re-instated and finally the outer polythene covering was sealed over the joint to form a fully watertight housing.
This procedure had to be followed several times between the Beach Joint and the Terminal Station as it was not possible to pull the whole land section length in as one section. Completing the land section took several days.
posted on Tuesday, February 3, 2015