The magnetron power was delivered via a rotating joint
to the antenna feed horn, which illuminated the 2 m circular dish antenna. There
was no method of power measurement available, and the custom was to place one's
hand over the feed horn to ensure that the magnetron was delivering at least
some power. This crude attempt at power measurement was also a very early example
of microwave cooking! As has been noted elsewhere(5), the mean power
of a radar magnetron, even such an early example as the CV76, was closely comparable
to that of the magnetron in a modern microwave oven. The CV76 was equipped with
a heater for the cathode, but the heater was switched off as soon as the magnetron
reached full power: thereafter, the cathode was heated only by electron bombardment.
The received signals ('echoes') were collected by the
antenna and passed, via the feed horn and rotating joint, to the vertical waveguide
run leading to the magnetron. However, they were inter-cepted about 30cm above
the magnetron by a TR (transmit/receive) cell clamped to the narrow wall of
the waveguide, to which it was coupled by a slot in the wall. The TR cell (fig.
6) ingeniously combined a toroidal resonant cavity and a gas discharge device.
During the transmitter pulse, the gas discharge across the centre of the cavity
effectively threw an open-circuit across the waveguide wall slot, and confined
the power to the waveguide, save for the small fraction needed to sustain the