John Bubb

Parametric Amplifiers (PA - Yellow Boxes)


The parametric amplifiers received their signal from the waveguide leading to the parabolic billboard-style antennas. The received signal was in the UHF band at around 1000 Megahertz. The parametric amplifier enhanced and then converted the signal to an intermediate frequency of 70 Megahertz. There were four parametric amplifier units in each direction (eight in total), one for each receiver. In the picture they are the four almost square units, two at each end of the receiver bank and have round meters at their centre points. Part of the (black) waveguide can be seen at roof level.

Receivers (R - Green Boxes)


There were four receivers at each end of the building. Two receivers (actually their associated parametric amplifiers) were tuned to each transmitter at the transmitting site. This allowed one receiver at a time to be disconnected for preventive maintenance while still being able to receive from both transmitters using the remaining three active receivers. Receivers acted on the 70 Mhz Intermediate frequency provided by the parametric amplifiers. Reception was frequency modulated and intelligence was extracted by a travis discriminator. Intelligence bandwidth was about 5 Megahertz. The outputs of all active receivers were applied to a delay equalizer that selected the best possible received signal at all times. Receivers contained a pilot alarm that went off whenever the received signal was lost. At times of poor propagation these alarms kept the technicians running for most of their shift.

These pictures show the north receiver bank actively receiving signals from Resolution Island. The parametric amplifiers are the square boxes with the central meter. The four receivers have removable metal covers and can be identified by the two round meters showing in each lower unit. A portion of the black antenna waveguide and coaxial feeders to the parametric amplifiers can be seen at upper centre of the first picture. The two mobile cabinets contain receiver test and alignment equipment.