-Stille steel tape recording machine.

At the beginning of the century Professor Poulsen, one of radio's
earliest pioneers, discovered that a magnetic impression could be made
on a moving length of wire which remained on the wire even after it
had been rolled up. He used his machine to record the Morse code
only, that is magnetism 'on' and 'off'. In 1924 Dr. Stille in Germany
made a machine which could record sounds. The B.B.C. sent two
engineers to Berlin, and after a demonstration they offered to buy the
machine, but in the end they returned to England empty-handed.

In 1931 Mr Louis Blattner managed to buy a machine and bring it
to England. He called it the Blattnerphone. By this time Dr. Stille
had replaced Poulsen's wire with a flat steel tape 6 mm wide. Each
reel of tape could only accommodate 20 minutes of recording. There was
a constant and heavy background hiss, due to the inherent quality of
the steel tape itself.

Stille Inventions Ltd. joined forces with Marconi's Wireless
Telegraph Co. Ltd. to produce, with the close co-operation of the
B.B.C. Research Department, the Marconi-Stille machine which was put
into use in 1934. The tape width was reduced to 3 mm and the
thickness to only 0.08 of a millimetre. In order to secure the
reproduction of the higher audio frequencies, it was found necessary
to run the tape at a rate of 90 metres per minute past the recording
and reproducing heads. This meant that the length of tape required
for a half-hour's programme was nearly 3 kilometres!

4. Brief description of the ribbon or velocity microphone.

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 so