WB1400 Warning Points

Introduction

The existing WB400/600 warning points were upgraded to WB1400 which included features to correct known fault liabilities on the old system. The WB1400 had a speech receiver for the spoken message from the police station control point and signalling receivers for the mains operated sirens. Their functions are described in the following sections.

The control unit at the police station was described in an earlier topic, if you have come directly to this page from a search engine there is a link to the Carrier Control point is included in the cross reference.

WB1400 Receivers

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

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

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. A link to circuit diagrams is included at the bottom of this page.

Like the WB400, the WB1400 speaker still 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 could send two different signals that switched on the loudspeaker of some or all or the receivers. Four pulses of 605Hz 'W' signal turned on the selected group and Eight pulses of 'W' turned on both groups. The user would not hear the 'W' signals unless their receiver was in the 'Test' mode. The ROC 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. The links below demonstrate the two prefix signals.

Note: - 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 within a few seconds of the message or signal finishing. 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 so.

Power Siren Control

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. The control signal frequencies and 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. A link to the circuit diagram may be found at the bottom of the page. The power siren part of the system was designed to be automatically self tested every 12 hours, whereas the earlier system was 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 pulsed G signal of 115mS On / 115mS Off, twelve times.