National Attack Warning Centre

The main source of the National Nuclear Attack Warning would be Air Defence Operations Centre ( ADOC ) at Strike Command in RAF High Wycombe with a back up at the Preston U.K.W.M.O. Sector Headquarters, located at Langley Lane, Goosnargh, Lancs. This table mounted unit would be used to issue the message to the 250 Carrier Control Points (CCP).

• The operator would turn the safety interlock key switch.
• Press the large Red operate switch.
• The speaking clock would be removed from all the national distribution rings.
• A one second burst of two simultaneous tones of 1200Hz and 1440Hz known as P+Q tones would be sent to sound the incoming message alarm in the CCP.
• When the "Speak Now" light illuminated the operator would announce the message into the dual microphones. This would be conveyed to the injection exchange for distribution on all four of the speaking clock rings.

 

Carrier Control Point - WB1400 Era

The United Kingdom is divided into 250 Warning Districts each served by a Carrier Control Points (CCP) installed in a Major Police Station in the district. This controlled the operation of Air Attack and Flood warning sirens and the broadcast of fallout messages.

This is the control unit (Equipment Carrier WB1400) housed in the operational area of a police station. A second identical unit was kept in reserve that could be deployed if the main unit fails. Anyone lucky enough to own one may be able to get it partly functioning.

This small control unit 21½"W x 11½"D x 17"H performs the same function as the two large control units plus two steel cabinets, each 1ft 10in wide x 1ft 2in deep x 6ft high in the police station apparatus room, which housed the signal generation and amplifying circuitry required by the first generation HANDEL system. The control unit pictured contains all the logic and signal generation within the box itself.

Each of the three handsets is at the end of a pair of wires from the Carrier Control Exchange (CCE). The two Red handsets are designated "X Path" and "Y Path". They receive broadcasts from Strike Command and have associated Red "Lift Handset" alarm lights and buzzers that are triggered before the spoken message. Providing there were no line faults both handset alarms would sound but lifting either would stop both alarms.

The CCP cannot talk back to Strike Command, but either handset may be used to broadcast local warning messages over the carrier system. The 72kHz carrier signal modulated by the Police Officers voice or siren control signal is sent over both the X and Y path back to the CCE. The same wires are also used to signal an alarm if the mains supply fails. A Black "Group" handset is for two way communication with the UKWMO Group Headquarters for this Warning District. It has a white alarm lamp "Group Tele" and buzzer.

This close up shows the control switches on the CCP. The siren can only be activated when the "MASTER" rotary locked switch located on the bottom right is turned to the on position. The verbal warning messages may be sent without this switch activated.

The two right hand keys are pushed upwards to sound their respective siren activation "ATTACK warning" or All "CLEAR" the "CANCEL" key stops the siren sequence before it has run its full course. The siren control signal which consists of a sequence known as G and S tones can be heard through the grill above the keys. They are described in the Power Siren Control Topic which follows later.

The same two keys held operated in a downward direction causes the warning receivers to be turned on to hear an "ALARM" or "CALL" sound followed by the spoken message. The rotary switch under these keys allows either the "SELECT" group of receivers or "ALL" the receivers to hear the message, by the use of two different "W" signals. This is explained further in the WB1400 Warning Point Topic. The "SPEAK NOW" light flashes for 7 seconds at the end of the alarm or call sound. During this period either of the Red handsets may be used to announce the message by pressing a small press-to-talk switch on the handset. The speak now light flashes during the message and for a further 7 seconds after the switch is released during which time further messages may be sent by operating the press-to-talk again. The modulation meters indicated to the operator the correct level for the spoken message. The needle should be within the thick Black line.

During periods when the CCP is not being used it generates a beeping confidence tone. Warning points can hear this confidence tone only when they press the test button on their receiver.

 

Demonstration of WB1400 signals
The sequence below demonstrates both the control signals and the tones and messages passed to users. The column headings indicate the two type of receiver owner and first column indicated what would be heard by any user with the test button permanently operated.
Any Receiver with the Test button operated	UKWMO Users WB1401	Public Warning Points WB1400
[Confidence Tone] tick-tick-tick	Nothing		Please single click the link below to hear the test message (50 Seconds duration). Users on dial-up will have to wait a few seconds whilst it downloads. WB1400 Demonstration (147 KiloBytes) Click the Windows Media Player, Play button to hear it again.
[Enable "SELECT" Signal] four rapid soft pips
[Call Signal] loud beeps "This is a test message for Royal Observer Corps personnel only."		Nothing
[Confidence Tone] tick-tick-tick	Nothing
[Enable "ALL" Signal] eight rapid soft pips
[CALL Signal] loud beeps "This is a routine test message for all users, you will now hear a demonstration of the alarm signal." [ALARM Signal] loud pips "Test Complete - Thank you."
[Confidence Tone] tick-tick-tick	Nothing

Carrier Control Exchange WB1400 Era

I don't have a photograph of the Carrier Control Exchange (CCE) equipment, but it is a taller version of the cabinet shown below in the distribution section. The equipment cabinet in the CCE received two feeds from different Speaking Clock distribution rings these are shown as 'Spkg Clock' circuits 1 and 2 in the diagram. These carry the speaking clock in peacetime and HANDEL message from Strike Control in case of an Attack.

The CCE consists of one control shelf and at least one distribution shelves. The thick double arrow lines represent the external lines to the Carrier Control Point (CCP). The 3 pairs of wires to the CCP leave on the left hand side. The X and Y paths are placed in different cables for security. Audio from the HANDEL interface goes towards the CCP. The 72kHz modulated carrier is received from the CCP.

The line between the CCP and the ROC Group is routed via a signalling converter (Unit WB1400/10A) when Group calls the CCP, the balanced battery signal from Group is converted to 25Hz ringing towards the CCP. The CCP calls group by placing an earth on its B-wire only, the converter sends balanced battery to call ROC Group Headquarters. Whereas the HANDEL circuits are unidirectional, the line to the ROC is bothway for speech and signalling.

The HANDEL interface (Unit WB1400/1B) amplifies the audio from Strike Command in the direction of the CCP. It detects a 1200Hz plus 1440Hz P+Q signal lasting for more than 1 second sent immediately before the warning message and converts this into a 180Hz signal of 711mS duration to alert the CCP. A filter blocks the carrier coming back from the CCP over the X and Y paths from the audio amplifier.

The carrier from the CCP should be received along both the X and Y paths. A preamplifier (Unit WB1400/2B) in each path monitors the carrier, if it fails, a signal is passed to the changeover unit (Unit WB1400/7B). The changeover unit control signal allows only one of the pair of pre-amplifiers to turn its output on. Whichever output is enabled feeds the carrier to the distribution shelf in the cabinet. Should one path fail the other path is selected. A manual changeover button is also provided.

 

Carrier Distribution between Exchanges

Unlike the previous system the X and Y carrier paths only extended as far as the CCE and not further too large towns. Now all towns and villages had only a single feed. The security of supply was considerably improved as the loss of carrier at an exchange would raise a maintenance alarm. By the time the WB1400 was introduced the majority of more vulnerable rural exchanges were fed by underground rather than overhead cable.

 

Carrier Distribution to Warning Points

These photographs (taken at the Avoncroft Museum, Bromsgrove 15/07/04) show how the Equipment Carrier WB400A and Box Battery WB400A, formerly used for the WB400 system was modified to house the WB1400 distribution equipment. The cabinet is part of the exhibit of small rural dependent exchange 'UAX13' at the museum.

The main cabinet is 1'-10½" wide, 1'-0½" deep, its height above battery box 2'-8". The Battery Box is 1'-10½" wide, 1'-2" deep, 1'-11" high. Both are made of heavy gauge steel and are connect to the Main Distribution Frame via a conduit for the cables.

Taking off the screwed on front cover reveals an Equipment Carrier WB1402, Diag. WB29604; a shelf of slide in units which may be dropped forward to give access to the cards. In the enlarged view a strip indicating which unit fits in the position can be seen along the bottom of the shelf. For example 4B is a Unit WB1400/4B

The incoming carrier signal from the previous exchange enters the shelf via the Filter Unit which sends the signal to the pre-amplifier a Unit WB1400/2B, should the incoming signal fail a fault alarm is raised via the Unit WB1400/8B which also handles the power supply to the shelf. Power is normally obtained from the exchange 50 volt supply, should this fail, the reserve battery under the unit will take over. The output from the pre-amplifier is connected to the inputs of 3 x Unit WB1400/4B Distribution units. Each distribution unit further amplifies the carrier and provides 5 outputs. Any of the 15 outputs can be connected to outgoing junctions to feed dependent exchanges or used to supply customers lines to warning points.

The shelf can be fitted with 5 x Unit WB1400/5A. Each can supply up to two customers lines with the trickle charge for the Speech Receiver. The unit also detects the signal returned from the Siren Signalling Receiver in response to the automatic test signal sent by the CCP. If the trickle charge fails (Line broken) or the test signal is not returned from a siren control unit a telephone exchange maintenance alarm is raised.

If the Unit WB1400/5A fitted in the last shelf position is removed and replaced by a Unit WB1400/6A, it produces two demodulated audio feeds instead of 2 trickle charge feeds. The audio feed is only used in a limited set of circumstances when it is not possible to serve a dependant exchange by carrier. This could occur if the line loss at carrier frequency exceeds the maximum permitted or the exchange is connected by a radio link. At the dependant exchange the Unit WB1400/2B is replaced by a WB1400/3A which modulates a locally generated 72kHz carrier with the incoming audio signal.

 

Local Distribution to Warning Points

To provide a customer with WB1400 their exchange line circuit is routed via the trickle charge feed and monitor unit, then out to line. A carrier supply from the one of the fifteen outputs from the three distribution amplifier is connected to these same line connections. A filter within the monitor and trickle feed unit prevents the carrier being shunted by the customers exchange equipment.

At the customers premises, a Filter 3A is used to block the carrier from the telephone instrument. The RECR terminals on the filter that were used for the earlier system's receiver are left disconnected. The WB1400 Carrier Receiver is connected directly to the line so it may receive the carrier and trickle charge it battery.

To answer questions raised on news groups:
Q: If anyone acquired / stole a receiver, would it have worked on their home phone line.
A: NO, A receiver would only work on a specially designated Civil Defence line that was fed with the carrier from the telephone exchange. Post 1992 they won't work at all.

 

WB1400 Warning Receiver

Here are two views of the speech receiver, the first has the cover on. The right hand photo has the cover and RF board shield removed to show the printed wiring boards. Two different types of loudspeaker unit could be connected to the receiver.

The speech broadcast receivers were line powered, a small current trickle charged the receiver battery, the blue canister in the pictures above. The top circuit board demodulates the 72KHz amplitude modulated carrier and controls the trickle charging. The lower board contains the power amplifier and 'W' signal detection logic.

The left hand design of speaker, the Loudspeaker Unit WB1400 was suitable for office type environments. The ruggedised Loudspeaker Unit WB1401 was used in damp and harsh areas such as ROC posts.

The WB1400 speaker had to be turned on by the user but it would be silent until called by the Carrier Control Point (CCP). To check it was working the test key could be operated to hear the 'Confidence Tone'.

The CCP has a rotary switch that sends two different tone signals to turn on the loudspeakers of some or all or the receivers. Four pulses of 605Hz 'W' signal turned on only the selected group and Eight pulses of 'W' signal turned on every receiver in the area. The user would not hear the 'W' signals unless they held the 'Test' button on the speaker in the operated position. The ROC locations were in the 'SELECT' group which enabled the police to broadcast messages to them during ROC exercises without affecting the general users. Once the receiver speaker was turned on by the 'W' signals, a 6.4 second blast of 'Alarm' or 'Call' signal preceded the spoken message.

Confidence Tone

This tone is generated by the Carrier Control Point when it is not sending speech broadcasts or control tone signals. It starts again when the message or signal finishes. It gave the recipient confidence they would receive a message if it is sent. I have had queries from people who thought the tone went off after the Attack Warning and came back on after the All Clear, that is not correct.

 

WB1400 Warning Point User Instructions

In Derbyshire, Warning Point operators were provided with a twelve page manual describing the function of the U.K.W.M.O. and giving detailed instructions on testing the receiver and ultimately the war situation. It covers the use of the siren, maroons and radiac monitoring unit.

A close facsimile of the document has been reproduced here, trying to keep the same words on every line, it was created from a scan of the booklet kindly provided by R o d d y   B u x t o n. He was given it by the engineer recovering the WB1400 receiver from Courtaulds in Spondon.

To prevent undesirable indexing of this PDF document by Web Crawlers, it has been encoded and requires the stated password to be used Note: it is case sensitive. I am sorry if this is a nuisance but html allows whole pages to be excluded from search engine indexes but not documents linked from a page.

If you wish to link to the document, please use
http://www.ringbell.co.uk/ukwmo/Page213.htm#booklet
to come directly to this subsection.

 

Siren Point

Externally the siren control equipment known as a 'Receiver Signalling' looked almost identical to the 'Receiver Speech'. The receiver demodulates the 72KHz carrier and filters out two control tones known as 'G' the guard signal and 'S' the siren signal. These control signal frequencies and their duration remained the same as the superseded system, the 'G' signal (1500Hz) was pulsed 400ms On / 400mS Off twelve times, to prime the logic to accept the 'S' signal (2160Hz) that turned on the siren motor. The duration of the 'S' signal determined how long the siren motor would be energised for.

The power siren part of the system was designed to be automatically self tested every 12 hours. Should the self test fail or the line become faulty an Exchange Maintenance Alarm would be raised. The previous system was only tested six monthly and required a visit to each siren point to check the test lamp was glowing and reset it. The air attack warning remained as eight, four second blasts of the siren at four second intervals. The all clear signal sounded the siren continually for sixty seconds.

The previously separate flood warning system known as WB601 was included in the WB1400 facilities. The flood signal was six siren blasts for thirty seconds at fifteen seconds intervals. To allow discrimination between sirens used for Air Raid and Flood, the later used a shorter duration pulsed 'G' signal of 115mS On / 115mS Off, twelve times.

At the siren location a manual control box was provided by the Home Office. This is usually in close proximity to the Carrier Signalling Receiver. The box has a screwed on hinged cover. The buttons allow local control of the siren. It was normal peacetime practice to remove the fuses for the Air Raid siren motor to avoid it being set off but in areas prone to flooding this wasn't possible.

 

Test Equipment

Roy has kindly sent this photograph of a Tester WB1401A from the Belfast ROC Museum. This multi function test box can simulate the Carrier Control Point ( CCP ) and also monitor the actual WB1400 carrier as it passes through the various parts of the network from the CCP to the Receiver.

In simulation mode, it generates a carrier modulated by the control signals 'call all' 'call select' 'attack' 'flood' generated by a CCP to alert speech receivers and sound both air raid and flood sirens, allowing the receivers to be functionally tested. It will also simulate the exchange power feed to the receiver battery. In monitor mode, it serves as a Level Measuring Set ( LMS ) for both audio and 72KHz carrier in the range of -60 to +20 dB. It will also monitor the demodulated audio on the carrier being received by the LMS and the test signals generated by the CCP simulator. This actual unit was manufactured in 1984 to diagram WB 29754, its dimensions are 45 x 26 cm.

In the lid of the tester is a further small test unit used when testing Signalling Receivers so a functional test can be performed without sounding the siren. The Tester WB1403A is connected into the mains wiring of the signalling receiver and has lights to indicate mains is present and when the siren would operate. The tester prevents the actual operation of the contactor relay that applies the Three Phase mains supply to the siren motor.

 

Feedback

I have had two very interesting email exchanges regarding this topic that are worth sharing with everyone.

The firstly in October 2009, Neil, a system designer for the second generation of HANDEL got in touch. He was able to answer a number of technical questions. In the BT film made for the introduction of WB1400, a routine test is made of the ADOC control equipment where the voice says 'Leeds' testing. This puzzled me, so I asked Neil if there were any sites other than High Wycombe and Preston, NO was the answer.

Another email in November 2011 from Jack, part of which is reproduced below answers the 'Leeds' puzzle. He also mentions the first correspondent too. It appears that Leeds and also Plymouth were code words for the real locations at Preston and High Wycombe, so it was my fault for not asking Neil the right question two years earlier.

The 'Schweppes' equipment that Jack refers to is the Operating Unit at the very top of this page. In the Sixties and Seventies the soft drinks manufacturer Schweppes used the sound Schhh... and the phrase 'The Secret of Sch' in their adverts featuring William Franklyn. Many of these adverts can be found on YouTube if you are interested.