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.

Carrier Control Point
Roll your mouse over the Diagram for a description of the parts of the CCP.

Block Diagram of the CCP

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 and 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 lamp and sounder above 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. In addition to the two HANDEL handsets, a third black handset connected the CCP with the ROC Group Headquarters switchboard. Fallout messages would come from the ROC 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 signal which was something 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.

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 and Y paths to the Carrier Control Exchange.

To sound the sirens, it was necessary to turn a Yale key on the Siren Control Unit (Control Unit WB600A). The circuitry was designed that each time the siren button was pressed each of the two Tone Generators would take it in turn to generate the control signals these fed both the Working and Reserve WB400 Modulators. Therefore if on pressing the attack warning button the tone sequence did not start due to a fault pressing the button a second time would engage the other generator.

Two audio tones were employed, a 1500Hz G-signal and a 2160Hz S-signal. To prime the siren circuit, the G-signal was pulsed 0.4 Seconds on and 0.4 Seconds off for 10 seconds. This was followed by a pulsed 4 Seconds on and 4 Seconds off S-signal, for the Attack Warning, or 60 Seconds of S-signal for the All Clear.

As a safeguard against failure of the siren control unit in the Police Office each of the generators had a set of buttons and Yale for local control from the apparatus room.

Police Routine Functional Test

Speech Receivers

Every six months the police performed a test of the speech broadcast system. Before the test each Warning Point was sent a card advising them of the date and time 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. The link below has a recording made by Bob Pickwoad at Newick ROC Post during one such test in 1966/7. I am very grateful to Bob for offering me a copy of the recording for this site.

Recording of a Routine Test

Transcript: [Confidence Tone] tick-tick-tick [Call Signal] pip-pip pip-pip This is the Tunbridge Wells Carrier Control Point making a routine test broadcast. You are now to hear a short test of the Warning Signal. [Warning Signal] wow-wow Now please take your question form and enter the word Domino at item number four. Please complete the form and forward it to the Chief Constable of your District today. Thank you. [Confidence Tone] tick-tick-tick

Please 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. WB400 Test Message . M P 3 (147 KiloBytes) Click the Windows Media Player, Play button to hear it again.

Remote Siren Test

To test the siren remote control box the " Test " button would be pressed on the Siren Control Unit (Control Unit WB600A) on the CCP. This button could be used without operating the Master Switch. Over the next few days, police officers would visit the siren locations and check that the test lamp on the control unit was illuminated. The officer would note any location that didn’t perform and reset those that did by pressing the lamp to stop it glowing. Any faults were reported to the Post Office telephone repair service.

Carrier Control Exchange (CCE) - WB400 Era

The Carrier Control Exchange (CCE) is the telephone exchange that served the Carrier Control Point (CCP). I do not have a photograph of the 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 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.

This photograph (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. The actual dimensions of the CCE hardware: 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.

The equipment was connected to the CCP at the Police Station by two pairs of wires, shown leaving the left hand side of the diagram above. These were identified as the X and Y paths. Each pair of wires to the CCP transmitted audio messages from Strike Command in one direction and received the carrier signal for amplification and distribution.

The CCE received two feeds from the Speaking Clock distribution rings. Each was split to serve both the Civil Defence equipment and the public speaking clock. In the public speaking clock each of the two feeds were amplified with one working (serving customers) and the other on standby (to a dummy load). Should either feed fail an exchange alarm would be raised and if necessary the standby amplifier used instead. Should both fail then Number Unobtainable Tone would be connected to anyone dialling the clock so they would not be charged for the call. During the Cold War period the speaking code was 8081 and 123 in large cities. This was standardised nationally to 123 in April 1995 when the speaking clock rings were decommissioned.

The audio from the speaking clock feed was amplified in the CCE equipment and sent down the X and Y path towards the CCP at the police station. The same X and Y path wires brought the 72kHz carrier signal back to the exchange. In case one path should fail the two carrier signals were monitored in a change over unit. 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.

Carrier Distribution

The Carrier Control Point (C.C.P.) for a warning district, generates two identical carriers sent over the X and Y path to the Carrier Control Exchange (C.C.E.). In the diagram these are shown in Red and Blue. To guard against damage to the underground cables, the X and Y paths are kept physically as far apart as possible. At the C.C.E., the X and Y carriers are amplified and forwarded to other dual fed exchanges, only one such exchange is shown here as the Large Town. If additional amplifier are fitted on the dedicated X and Y paths this exchange may extend the duplicated paths to other double path exchanges.

At the dual fed exchanges including the CCE, a changeover unit monitors the incoming carriers. Should one fail, it selects the other. This switched supply (shown in Green) is amplified and distributed to the Warning Points in the town. If it is necessary to extend the distribution to villages, these are fed from the switched supply.

In the 1960-70 era, many villages only had a single underground cable feeding the exchange, so there was little point in duplicating their carrier feed. In more remote locations, one cable passed through a number of exchanges. In the diagram, village C is supplied from village B. There were design rules that limited the number of tandem links that could be used. Quite often small village may have only have had one or two warning points to feed.

 

Local Distribution to Warning Points

The telephone line going to the warning point was used to convey the WB carrier to the receiver or siren. In the 1960-70 period, lines were often in short supply, waiting lists for phones was not uncommon and two customers may have shared the same pair of wire back to the exchange in what was known as shared service or party line. Sending the carrier over the existing phone line removed the need for an extra pair of wires.

In the WB400 equipment at the exchange, the carrier was amplified and divided into a number of individual supplies, one for each warning point. A connection was made from the carrier distribution unit to the line towards the customer. To prevent the Exchange Line Circuit from shunting the carrier, the wiring was altered so an inductor unit was introduced. Inductors block the passage of the higher frequency of the carrier whilst still allowing the direct current and ringing for the telephone through.

At the warning point, the telephone is rewired via a filter unit. This separates the direct current and ringing from the LINE and sends it to the INSTrument connection whilst blocking the carrier, so the telephone (telephone instrument as they were called) does not shunt the carrier. The filter's other connection point has the opposite effect, it allows the carrier to pass and blocks the passage of direct current and ringing, so the RECeiver does not affect the operation of the phone, whilst allow the higher frequency of the carrier to pass.

It should be noted the receiver would only work on specially designated lines fed with the carrier from the exchange. Ordinary telephone lines did not have the carrier signal on them. To answer questions raised on news groups: Had anyone acquired / stolen a receiver, it would not have worked on their home phone line.

 

Distribution with Buildings

In large industrial premises the siren or speech receiver may be situated in a part of the building remote from the point where the telephone lines came into the building. In these type of premises there would be a number of incoming exchange lines to the company’s switchboard or Private Automatic Branch Exchange ( PABX ). It may be that the Warning Receiver was located in a permanently staffed control room. The use of dedicated pairs of wires to the speech receiver was a possibility but this represented a fault liability.

A way was found to bypass the carrier around the switchboard or PABX as it could not pass through it. A Filter Unit 3A separated the 72kHz carrier being sent over one of the exchange lines. The carrier signal was introduced back onto the selected extension line by using a Filter Unit 4A as shown in the diagram on the right. This would wend its way through the building. A further Filter Unit 3A located near the telephone extension separated the carrier to feed the Warning Receiver.

The Filter Unit 4A allows easy passage of the carrier from the CARRier to the extension ( EXTN ) whilst blocking it from going towards the EXCHange. Audio, ringing and direct current to energise the telephone extension pass easily between EXCH and EXTN but are blocked from going to the CARR terminal and causing overhearing between the exchange line and extension.

 

WB400 Carrier Receiver

The WB400 receiver was powered by a six volt dry battery in the base and when correctly adjusted would emit the quiet tick of the confidence tone sent by Carrier Control Point. When a calling signal or speech message was transmitted, the volume increased automatically.

In peacetime the receiver was normally switched off and only turned on for tests. The red knob on the front is a combined On/Off and Volume control. Below that is a small pull out draw containing an instruction card. The card told the user what to do in response to a message and how to change the battery which required the removal of the base plate.

On many occasions the receiver would be accidentally left on and flatten the battery or the user would forget to switch it on for the six monthly test message. When the replacement was designed, these shortcomings were overcome by feeding the power from the telephone exchange. It seems strange that it was still necessary to turn the receiver on when required and this was not done automatically.

This is the internal view of the Receiver Carrier WB400 (Diagram WB 28013). To protect the electronics, the chassis plate has a cork seal, a plastic membrane covers the rear of the speaker grill. A desiccator unit is fitted to the chassis plate which may be viewed from the battery compartment to check it is still Blue, if damp gets in the colour changes to Pink.

The four square cans are on the RF board which amplifies and detects the audio on the 72kHz carrier. The second board is the audio board containing a squelch circuit to mute the output when the confidence tick tone is being received. Next to the audio board is the output transformer with two transistors mounted on its tags.

 

WB400 Warning Point User Instructions

Instructions for the Warning Points were given on a small folded card held in a drawer in the base of the receiver unit. The card is reproduced below.

Warning points would have a hand operated siren to sound the Attack Warning and the All Clear in rural areas without power sirens.

In this picture of a policeman preparing to give a fallout warning, the maroon is held in place with sandbags and operated remotely with a battery. Once triggered it sends up three maroons spaced a few seconds apart.

 

Circuitry

There was no Electro-Magnetic Pulse (EMP) protection in this receiver. This was due to the WB400 equipment being designed before the phenomena of the EMP was discovered. The American " Starfish Prime " test on 9th July 1962 affected telephone and power systems 900 miles away in Hawaii. A Russian test on 22 October 1962 when a 300kt warhead was detonated at 290km altitude apparently affected 570km of telephone lines and started a fire that burnt down the Karaganda generating station.

The circuit is actually very simple for this is a 72kHz AM receiver that gets its signal from the line rather than an aerial and employs Germanium junction transistors. The RF board has three CV7005 (OC71) transistors, the audio board one more CV7005 more with two CV7006 (OC72) output transistors and two CV7004's (OC45) in the squelch. Transistors VT1 and VT2 amplify the incoming signal. TV3 is the AM detector that feeds the volume control. The audio push pull output stages comprise VT4, 5 and 6. A small amount of audio is fed into what is called the suppressor circuit. This reduces the gain of the audio output stage when the tick is present. If a spoken message is received the gain is increased so it may be clearly heard but the confidence tone should sound like a clock ticking.

 

Siren Control System WB600

Police Station Equipment

Mounted on the front of the "Operating Unit WB401A" was a small panel, a "Control Unit WB600A", consisting of interlocking push buttons, each containing a small lamp and a key-switch. To activate the sirens, the key-switch must be operated with a key, which was often kept in a break glass unit. Pressing either the top right button for the Attack Warning or top left button for the All Clear would activate the remote sirens. In between the two siren buttons was a third Stop button.

In the apparatus room, duplicate "Unit Signalling WB600A" generated the tone signals used to modulate the WB400 carrier. Each "Unit Signalling WB600A" had a "Control Unit WB600A" mounted on it, the sirens could be controlled from this point too. Two audio tones were employed, a 1500Hz G-signal and a 2160Hz S-signal. To prime the siren circuit, the G-signal was pulsed 0.4 Seconds on and 0.4 Seconds off for 10 seconds. This was followed by a pulsed 4 Seconds on and 4 Seconds off S-signal, for the Attack Warning, or 60 Seconds of S-signal for the All Clear.

Siren Point Receiver

At the siren point, a "Receiver Carrier WB600" looking like a grey plastic box approximately 21 inches wide by 7 inches high and 7½ inches deep, was connected to a telephone line via a "Filter Unit WB600A". The receiver was wired into the Home Office’s electric mains circuits controlling the siren.

{ Sorry no picture }

The circuitry contained a 72kHz carrier receiver, the audio output of which could be monitored on the back panel. This audio was amplified and filtered to extract the remote control signal tones. Two audio tones were employed, a 1500Hz G-signal and a 2160Hz S-signal. To prime the siren circuit, the G-signal was pulsed 0.4 Seconds on and 0.4 Seconds off for 10 seconds. This was followed by a pulsed 4 Seconds on and 4 Seconds off S-signal, for the Attack Warning, or 60 Seconds of S-signal for the All Clear.

All this was done with Germanium Junction transistors, however the G-signal pulses were detected by a pendulum relay. This device swung back and forward in response to the G-signal pulses until after a few seconds the pendulum travelled far enough to make an electrical contact. This gave the necessary immunity to prevent the receiver being trigger by the warning message speech signals.

Approximately 6 seconds of pulsed G-signal primed the S-signal circuitry. The subsequent S-signal operated a small relay, which further operated the siren 3-phase Mains contactor. The siren could also be controlled locally from the autowailer, a small box on the Home Office equipment panel having buttons to sound the "Attack" and "Raiders Passed" warnings and a Stop button.

None of the WB400 or WB600 equipment circuitry contained any EMP protection. After a thunderstorm, it was in my experience, often necessary to replace faulty WB600 receivers especially those in water towers and other high points. After changing the receiver, it was good fun to run the siren for a couple of seconds. Thank goodness this was never heard for real.

The WB600 control signals modulate the WB400 carrier so the warning points on their “Receiver Carrier WB400” would have heard these. The instruction card did make mention of the remote control signal. I have made a reconstruction of the remote control signal's audio tones and siren sounding the attack warning.

Demonstration of Siren Control Signals
Description: This is a Stereo M P 3 recording, with the WB600 Control tones on the left channel. So that you can appreciate how they worked the siren sound is on the right channel.	Please click the link below to hear the demonstration (63 Seconds duration). Users on dial-up will have to wait a few seconds whilst it downloads. WB600 Demonstration . M P 3 (252 Kilobytes) Click the Windows Media Player, Play button to hear it again.

A Typical Air Raid Siren

Patrick Bean sent this nice detailed picture of a siren, to me. If you look carefully, two cables come up the pole. One cable connects directly into the siren body. This is the 3-Phase supply to the motor. The other goes to the 4 way junction box under the grey thermostat box. At the 3 and 9 O'clock position, wires come out to the fan units and go into another junction box where two 'Pyro' type of copper clad wires come out. These are the heaters to prevent the fans icing up in the British weather.

The first drawing shows the connections of the WB600 Siren control receiver unit to the Home Office wiring at the siren point.

The Home Office used a standard arrangement for the siren station as detailed in this sheet kindly used with permission of Russell Barnes. The siren station was often located close to the point where the electricity supply entered the building housing the siren as its supply was taken from the non-metered side of the incoming mains.

It was standard practice to locate the siren on a roof. Where a fire siren used to call out retained firemen was available this would be used for civil defence purposes too. If suitable premises didn't exist, the siren would be pole mounted and the control equipment housed in a street cabinet.

 

Test Equipment

Roy has kindly sent this photograph of a Tester WB400A from the Belfast ROC Museum. This tester was used to set the correct carrier signal levels in the CCP and Exchange apparatus and locate faults in the distribution network. It is a Level Measuring Set ( LMS ) tuned to 72KHz that displays the signal strength on the meter in the range of -65 to +25 dB. The unit also contained an speaker unit so the audio modulation could be heard just like listening to a warning receiver. The input terminals are on the bottom left hand side in this photograph. The designation plate shows it was made in 1962 to diagram WB28029.

The tester is in a rugged steel box approximately 24" x 18" x 6" and has a detachable lid. It weighs 5 or 6 Kg and I can recall climbing up a telephone pole with mine to locate a fault. I shudder to think what would have happened if I had dropped it on someone!

I am not aware of any other piece of test equipment being available to local exchange and field maintenance staff. This shortcoming was rectified with the introduction of the new generation of HANDEL.