George Papandreou, Greek Prime Minister of the war-time government
of National Unity in exile, is seen with the famous ribbon microphone
developed by the B.B.C. in 1934. This microphone (R.C.A.
designation 44BX) consists of a ribbon of corrugated aluminium foil
only 0.0002 of an inch thick suspended vertically in a very intense
but narrow magnetic field. When sounds vibrate the ribbon extremely
low alternating voltages are developed at the ends of the ribbon,
which has a very low impedance of only 0.15 ohm, necessitating the use
of a step-up transformer of 1:45 turns ratio very close to it. The
frequency response is 20 to 16,000 Hz. A drawback is that the ribbon
can be blown out of the magnetic gap by sudden puffs of air when a
speaker gets too close to the microphone, so the casing is lined with
several layers of chiffon which let in the sounds but not the air.
Without its base the ribbon microphone weighs 4 kilograms, nearly 9
lbs.
5. An outstanding antenna system designed by Rex G4JUJ for Phase III
amateur satellite communication.
The up-link section comprises four 88-element Jaybeam multi-beams
which provide a power gain of 225.
The two down-link 8 element yagis are each fitted with a small
D.C. motor directly coupled to a 9 inch length of M5 brass studding
rotating inside a block of PTFE linked to a push rod which can move
the antennas 75 degrees both sides of the vertical position, either in
unison or in opposite directions. This system provides infinitely
variable polarisation which optimises the down-link signal at any
instant.