Page 19 - Royal Observer Corps

Starting in 1981, the landlines to Group Headquarters were converted from switched Emergency
Circuits to permanently connected Private Circuits (Private Wires 'PW'). The previous arrangement
of switching the lines meant this could only happen for main exercises. Therefore, the Tele Talk
couldn't be used on a normal drill night. The change to permanent circuits made it possible to
communicate with the other posts in the cluster and Group HQ at any time.

The new Private Circuit to Group HQ operated over four wires, one pair conveying the both
speech to the post Tele Talk and the carrier plus power for the warning receiver. The other pair
conveyed the Tele Talk speech from the post and supplied the power to the Tele Talk unit. This
led to an improved quality of communications around the cluster and back to Group. The very
vulnerable overhead lines were replaced with an underground cable. At some sites the poles were
not actually removed by BT and in some cases are still present now.

During the mid-Eighties, the old valve VHF transceivers in master posts were replaced with
modern sets, still working on VHF, but using low band for improved coverage in comparison to
high band.
The original grey Tele Talk was replaced with the more modern AD8010. This derived its electrical
power from the public telephone exchange 50 volt battery via the private circuit thus removing the
need for a stock of batteries at the post. This new design of Tele Talk retained the simple controls
of the earlier model. The 'CALL' button calls the attention of Group. The device is normally in
receive mode and monitors any conversations taking place on the Private Circuit.

The 'TRANSMIT' button must be depressed to switch to talk mode. This is very much like
operating a radio transceiver. The loudspeaker and microphone are in the hinged lid that is
normally kept closed to press the 'ON' button down to switch it off. When in use, the lid could be
angled to suit the user, who speaks about 9-12 inches away from the microphone.

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