GPO Vehicles

Text taken from the
THE POST OFFICE ELECTRICAL ENGINEERS' JOURNAL
Vol. 55 Part 4 JANUARY 1963

The detection equipment is mounted in a modified Series 5 Morris Oxford Traveller, the panoramic receiver and power unit being in the position normally occupied by the nearside front passenger seat.  The operator sits in the nearside rear seat and a Postal and Telegraph Officer occupies the offside rear seat.  This change of seating position was found necessary during a trial of best practice and all new vehicles are now four door.  A shielded map-reading light is fitted to the rear of the driver's seat for the use of the postal officer.  The driver's view is unobstructed by the equipment except for the central mast tube and a periscope, which are visible in the internal mirror.  Wing mirrors are provided, the nearside mirror being adjusted to show the clearance between the aerial and roadside trees when the car is tilted by a steep road camber.  A 3-phase,self-excited a.c. shunt generator, belt-driven by the engine and operating at a maximum speed of 11,000reV/min, supplies a maximum output of 800watts.  The current in the rotating field-winding of the generator is controlled by a transistor-amplified vibrator-type regulator, and the stator output is rectified by bridge‑ connected silicon-junction diodes and used to charge the vehicle batteries.  The two series-connected 6-volt batteries of 110 ampere-hours capacity are enclosed behind the rear seat in sealed cases vented on the underside of the car.  The detection equipment is normally operated with the vehicle stationary and the engine idling.  Under these conditions the output of the generator is sufficient to balance the electrical load.  A fully‐screened and suppressed ignition system is fitted to the vehicle, and radio-interference suppressors have been fitted to the windscreen wipers, petrol pump, heater booster and clock.  The standard fresh‐air, heating and ventilating unit of 2-75 kW capacity utilizes waste engine heat.