Landline link to Group

In the early 1960's the original magneto type telephone with a headset worn by the observer that had been in use since the war was replaced with a loud speaking unit. Known as a TeleTalk the "Units Intercom LB AD 3460" to give its proper description allowed the observer to move around in the bunker.

It was a battery powered unit using the same design of 6 volt dry battery [Battery, Dry No. 27] fitted in the Warning Receiver. Additionally a 67.5 volt battery [Battery, Dry No. 18] was required for signalling Group. The TeleTalk is normally in receive mode so any conversation on the cluster line may be heard. Before speaking the small lever switch on the left hand side of the unit is pressed downwards. The loudspeaker is used as a microphone. To attract the attention of Group, the lever switch is pushed upwards to the CALL position and released.

As posts were usually located on remote hilltops the pair of wires feeding them were usually carried on poles along field boundaries. This would have made them very vulnerable to blast damage. The same wires connected the Warning Receiver and the TeleTalk unit so both would fail together.

Telephone engineers regarded these as a bit of a joke. In the film Hole in the Ground, the featured post sent an observer out in the fallout to clear the line faults caused by the bomb exploding. This was not an easy task in peacetime yet alone a post nuclear holocaust.

The circuit from the post to the nearest telephone exchange was a dedicated pair of wires. The remaining part of the circuit back to Group HQ normally consisted of one or more switched lines. In peacetime these carried normal telephone calls between exchanges. For Royal Observer Corp exercises, or in time of war these circuits were switched over for ROC use. Each circuit had a designation consisting of the letters 'EC' that meant Emergency Circuit and four or five digits e.g. 'EC1234'. Readers employed by the GPO / Post Office Telephones / British Telecom as switchboard operators may recall being involved with the switching of the EC's as they were known. Switching only happened for an exercise which meant that during a drill night there was no way to communicate with group.

Switching the Emergency Circuits was a complex task when considering that York alone had Forty posts in Twelve separate clusters. This was replicated up and down the country some Twenty Five times. Firstly a 'Busy' key stopped the line being used for telephone calls. If a call was in progress it had to be allowed to finish before switching. Much of this was done manually at staffed buildings but at small remote exchanges, the switching clerk had to dial-up three calls to two numbers in a set sequence and time interval. At the end of the exercise it all had to be restored to normal.

 

Warning Receiver

In order to receive warning of an Air Attack the Post was fitted with a Carrier Receiver. The single pair of wires used by the TeleTalk also conveyed the carrier to the Post. The operation of warning system and HANDEL are fully described in other topics on this site. The observers would respond to messages sent via the Carrier Receiver in the same way as another other warning point using the hand operated siren or maroons to warn the public.

This version of receiver was power by 6 volt dry-cell battery in the base of the unit. A stock of batteries [Battery, Dry No. 27] were kept in the post for this and the TeleTalk featured the previous sub-section. The battery pack contained eight 'C' size cells wired as two parallel groups of four cells in series in a waxed paper box.

The number 170020, is the (GPO / Post Office Telephones / BT) Item Code number, for ordering purposes. The smaller number at the bottom 4/72, indicates this battery was manufactured in March 1972. Unused batteries had their terminals covered with a wax paper strip to prevent short circuits.

 

Master Post Wireless Sets

The first trials of radio as a backup to the TeleTalk commenced in the autumn of 1961 in Winchester Group and in 1975 the last Groups were still awaiting equipment. Belfast had to wait for the second generation radios in the 1980's. The wireless set shown here is a ATE Countryman. Automatic Telephones and Electric Co. ( ATE ) was taken over by Plessey and some sets may be badged as Plessey.

Only the master post of the cluster was equipped with a single channel VHF radio allowing it to contact the Group independently of the TeleTalk landline. If it were still possible to communicate with the other posts in the cluster the master post would relay their readings to Group. Dual frequency simplex operation meant master posts could not communicate with each other. Adjacent Groups worked on different frequencies and as posts radios had only a single channel no other Group could be contacted if their own Group was knocked out. These issue were addressed with the second generation radios.

The radio set was to be mounted vertically with the connections facing down. The sets were wired to a small box under the shelf which comprised of the headset socket and Push-To-Talk switch. There was no volume control as this was preset on the radio. The AF Gain control may be seen in the large photograph of the connection panel.

Due to the limited range of VHF radios, Hilltop radio sites relayed the signals via VHF radio links back to the Group. Group HQ's were fitted with a wind up mast, carrying a number of VHF yagi aerials pointing at the hilltop sites. These also carried the inter-Group radio circuits described elsewhere.

All Master Post radios would listen to the hilltop site(s) on one frequency and transmit back to the hilltop on another frequency. Due to this frequency split posts could not speak to one another. This was the same technique employed on the Police and Fire Countywide Networks and whilst it meant Group was always in control of the radio waves there would be no post to post intercommunication if Group was destroyed.

During the time of my involvement, Bedford Group usually operated their radio scheme with talkthrough (they called it 'Bounce Back') turned on, allowing posts to hear both sides of the conversation. The diagram shown the actual frequencies used by the Bedford Group in the 1970's. Bedford Posts transmitted on 155.000MHz. The two Home Office hilltop sites at Old Poor's Gorse and Streetley relayed the Post transmission to Bedford Group on 168.425MHz. Bedford's messages were transmitted on a 174.125MHz link to the hilltops which rebroadcast it to Posts on 147.000MHz.

While it has been possible to find the "Era 2" low band frequencies shown on the next page it has proved more difficult for "Era 1" and any information for other groups would be most welcome. This table shows four of twenty five group frequencies.