UKWMO Warning System Detail

Handel

The code word HANDEL was used to describe the audio distribution system used to pass the attack message from Strike Command to the 250 Carrier Control Points, located in major police stations throughout the country. [Later discovery - Strike Command was located in High Wycombe, Bucks with a back up at the Preston ROC HQ located at Langley Lane, Goosnargh, Lancs] The existing speaking clock distribution system was utilised to carry the warning message around the country. Two separate clock distribution circuits fed the announcement from the London and Liverpool clocks to the major telephone Group Switching Centres. To guard against loss of the speaking clock, these were monitored and a fault alarm raised if either failed.

The speaking clock would be disconnected before a warning message was passed. The removal of the clock announcement causing the equipment in the telephone exchange to connect Number Unobtainable Tone to the public feed of the speaking clock and prevent any call charges being raised.

To alert the Police to an incoming attack warning message, a short burst of two tones, known as P & Q preceded the verbal instructions. For engineering test purposes, the three pips of the speaking clock changed from their usual 900Hz tone to 2500Hz at Nine O'Clock precisely, every day. The 2500Hz tone being midway between the P & Q tones.

Carrier System

Copper pairs between the exchange and customers premises are able to carry signals well above the range of human speech. This extra bandwidth may be used to carry signals without interfering with the normal telephone operation. ADSL is a modern system using this bandwidth, however other simpler systems known as "Wire Broadcast" (WB) have been around since the 1940"s. A paper read to The Institute of Post Office Electrical Engineers on 11th April 1949, describes the trial of a multichannel carrier system for broadcasting BBC programs over telephone lines. A carrier system was used to distribute the Police Messages and siren control signals, using existing telephone lines. This helped detect faults in the carrier system and saved the cost of providing extra wires to often remote locations. If the wires became disconnected the telephone would be reported faulty, long before the carrier system was next tested.

The system having a 72kHz carrier, amplitude modulated by speech and signalling tones used to convey the broadcast messages from the Police Station to the Warning Points was known as Carrier System WB400. Rather confusingly the WB400 carrier could be modulated by two tones to control the mains powered sirens, this part of the system was known as WB600.

The WB400 system started life in the early 1960's and was replaced in the early 1980's by WB1400 which continued until the scrapping of the whole UKWMO in 1992. The replacement WB1400 continued to use the same carrier frequency of 72kHz, enabling inter working during the phased changeover.

CARRIER CONTROL POINT (CCP) - WB400 Era

Control Panel

This photograph taken from the UKWMO booklet shows the control equipment at the Police Station. This was the business end of the equipment comprising the Carrier Control Point. (CCP) The control panels were wired back to the telephone apparatus room in the police station. In the apparatus room were two steel cabinets, each 1ft 2in deep x 1ft 10in wide x 6ft high, containing the electronics shown in the system diagram below. Roll your mouse over the picture for a description of the items pictured.

Roll your mouse over the Picture for an explanation of the object in the photograph.

CCP System Diagram

This diagram shows the basic connection of the various parts of the equipment at the Police Station, I don't ever recall seeing an official diagram showing how all the component parts went together to form the whole system, so I had to sketch out something similar to this drawing.

The CCP was connected to the Carrier Control Exchange (CCE) by two pairs of wires, shown leaving the right hand side of the diagram above. These were identified as the X & Y paths. Each pair carried audio messages from Strike Command, distributed via the speaking clock system and took the Carrier signal back to the CCE for distribution.

The two grey HANDEL handsets, mounted on the "Operating Unit WB401A" were connected to two separate audio feeds from the carrier control exchange. To alert the Carrier Control Point, two simultaneous tones of 2400Hz and 2600Hz known as P and Q tones, would be sent by Strike Command to trigger the sounder on the HANDEL phone. The police would listen to the message and act accordingly. As this was a broadcast system there was no facility to talk back to the Strike Command or between Carrier Control Points. In peacetime, the speaking clock could be heard on the X and Y path HANDEL phones. As well as the two HANDEL handsets, a third black handset not shown on this diagram, connected the police with the R.O.C. Group Headquarters switchboard. Fallout messages would come from the R.O.C for onward broadcast to the warning points.

Warning messages would be broadcast from the "Operating Unit WB400A", which consisted of a microphone, modulation meter and a number of keys on a sloping fronted box. The keys sent pulsating tones before each verbal message. One sound was known as "Call" and the other "Attack Warning", the later must not be confused with the attack warning siren control which was completely different. A confidence "Tick" sound was generated when not in use. Further down this page, a recording of a routine test message carries both these signals. You may listen to the confidence tone signal at the bottom of this page.

The "Operating Unit WB400A" was normally plugged into a multiway jack connected back to the "Working" carrier generation equipment housed in an "Equipment Carrier WB404A" located in the telephone apparatus room. Another multiway jack was wired back to the "Reserve" side of the carrier equipment. In the case of a fault, the operating unit could be changed over to the "Reserve". A spare "Operating Unit WB400A" was housed in the "Equipment Carrier WB404A " normally plugged into the "Reserve" side. This could be used in situ or retrieved and used in the police station office.

The output from both Oscillator units was monitored, if the Working side failed, the Reserve would be switched in automatically. The protected feed was split two ways and sent on two separate X & Y paths to the Carrier Control Exchange.

To sound the sirens, it was necessary to turn a Yale key on the Siren Control Unit. The circuitry was designed that each time the siren button was pressed, each of the two G + S Tone Generators would take it in turn to generate the tones, these fed both the Working and Reserve WB400 Modulators. Therefore if on pressing the attack warning button, the G tone sequence did not start, due to a fault, pressing the button a second time would engage the other generator. More details of the G + S tones are given on the Siren System Page. Each of the generators had a set of buttons and Yale for local control from the apparatus room.

Routine Testing

Every six months a test of the Speech broadcast system was performed by the police. Before the test each Warning Point was sent a card advising them of the test. This had to be completed and returned to the police liaison point, who reported any faults to the telephone fault repair service. Below is a recording made in 1966 or 67 by Bob Pickwoad at Newick ROC Post during one such test. I am very grateful to Bob for offering me the recording for this site.

Carrier Control Exchange (CCE) - WB400 Era

CCE Hardware

I do not have a photograph of the CCE hardware in the exchange, known as an Equipment Carrier WB405A and Box, Battery WB401A. It is a very uninteresting grey steel cabinet with a screw on front cover. It is a larger version of the one shown in the photograph below. The cabinet is mounted on a slightly deeper grey steel battery box, with a similar screw on cover. The box contained large dry cells that would power the equipment if the exchange 50 volt battery supply failed.

These photographs (taken at the Avoncroft Museum, Bromsgrove 15/07/04) show the Equipment Carrier WB400A and Box Battery WB400A, as used at single path dependent exchanges, this is only 3ft 8¼in compared with 6ft for the CCE unit. CCE Dimensions Equipment Carrier WB405A, 1-10½ wide, 1-0½ deep, height above battery box 4-1. Weight empty 175lb, plug in units 35 - 55lb. Box Battery WB401A, 1-10½ wide, 1-2 deep, 1-11 high. Weight empty 40lb, batteries 185lb.

CCE System diagram

This is the exchange that served the Carrier Control Point. The equipment was connected to Police Station by two pairs of wires, shown leaving the left hand side of the diagram above. These were identified as the X & Y paths. Each pair transmitted audio messages from Strike Command, and received the Carrier signal for amplification and distribution.

Two feeds from the Speaking Clock distribution rings which in wartime, would carry the messages from Strike Command, were sent out to the Police Station over separate X and Y paths. The public feed of the speaking clock, was connected to customers dialling the code 8081 (today 123 is used), via duplicated monitored amplifiers. Should either feed fail, its loss was detected and the other path would be used instead. Should both fail, Number Unobtainable Tone would be connected to anyone dialling the clock, they would not then be charged for the call.

The same X and Y path wires brought the Carrier signal back to the exchange. The two feeds were monitored in case one path should fail. This protected feed was amplified and fed the local warning points and also be sent over inter exchange junction circuits to other remote exchanges for distribution to their warning points too. If there were other major towns in the Police Station's warning district, those remote exchanges may have been dual fed with the carrier. In this case, the X and Y paths were connected directly to amplifiers and distribution units, with one feed from each side connected to two inter exchange junction circuits. At a dual fed remote exchange, as similar arrangement amplified the incoming signals and select one of them for further amplification and distribution to its warning points. This is described in more detail in the topic on carrier distribution.