broadcasting was the speech signal. At the receiver, filtering out the carrier
leaves the speech signal which we then hear through our speaker. By the early
1930s the two established methods of modulating the carrier in radio
transmitters were widely accepted to be wasteful of power. Robert’s
‘series-modulation’ provided a more efficient method of modulating; the
transmitter being fed with current varying according to the speech current
received from the microphone(s), and radiating power correspondingly. The
method was especially applicable therefore when large amounts of power were
to be modulated and provided a much higher quality signal which in turn
vastly improved reception for the listener. Series-modulation was therefore
ideal for the new ‘super-broadcasting’ stations and although an alternative
system, ‘phase modulation’, had been developed by the Société Française
Radio-Electrique, GEC-Marconi did not consider it to be superior to, or had
any economic advantages, over series modulation—even though
Radio-Luxembourg and the French state broadcasting stations were already
equipped with this system. Robert’s series-modulation was subsequently
widely adopted in telecommunications.
16.2.4 CAT Valves and British Broadcasting
The first water cooled transmitting valve made by the company, naturally
called the ‘CAT1’, was similar to an earlier American design. Each valve could
accept 10 kW of input power when used as an RF amplifier and these valves
were employed at the Rugby radio station of the G.P.O. in Warwickshire
(alongside demountables, Chap. 15), at the Marconi wireless station in
Caernarvon North Wales, (where 48 old glass valves in parallel were replaced
by 10 new CAT1 valves), and at the new BBC long wave station at Daventry
in Northamptonshire in 1925. With an overall output of 25 kW, at the time
Daventry was the most powerful transmitter in the world. Later in 1934
(Sect. 16.5), the new larger Droitwich transmitter adopted the frequency and
the famous Daventry ‘5XX’ call sign, but Daventry was retained, firstly as a
reserve for Droitwich, and later for transmitting coded messages across
Europe during the second world war. The availability and the raw power of
the transmitter during the 1930s also saw Daventry host probably the most
important pre-war experiment ever in the UK, an experiment that laid the
foundations of a technology that more than any other contributed to the
successful outcome of the 1939–45 war, viz, the ‘Chain Home’ (CH) and
‘Chain Home Low’ (CHL) ‘radar’ stations and the airborne radars.
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372
D. Sheppard
leaves the speech signal which we then hear through our speaker. By the early
1930s the two established methods of modulating the carrier in radio
transmitters were widely accepted to be wasteful of power. Robert’s
‘series-modulation’ provided a more efficient method of modulating; the
transmitter being fed with current varying according to the speech current
received from the microphone(s), and radiating power correspondingly. The
method was especially applicable therefore when large amounts of power were
to be modulated and provided a much higher quality signal which in turn
vastly improved reception for the listener. Series-modulation was therefore
ideal for the new ‘super-broadcasting’ stations and although an alternative
system, ‘phase modulation’, had been developed by the Société Française
Radio-Electrique, GEC-Marconi did not consider it to be superior to, or had
any economic advantages, over series modulation—even though
Radio-Luxembourg and the French state broadcasting stations were already
equipped with this system. Robert’s series-modulation was subsequently
widely adopted in telecommunications.
16.2.4 CAT Valves and British Broadcasting
The first water cooled transmitting valve made by the company, naturally
called the ‘CAT1’, was similar to an earlier American design. Each valve could
accept 10 kW of input power when used as an RF amplifier and these valves
were employed at the Rugby radio station of the G.P.O. in Warwickshire
(alongside demountables, Chap. 15), at the Marconi wireless station in
Caernarvon North Wales, (where 48 old glass valves in parallel were replaced
by 10 new CAT1 valves), and at the new BBC long wave station at Daventry
in Northamptonshire in 1925. With an overall output of 25 kW, at the time
Daventry was the most powerful transmitter in the world. Later in 1934
(Sect. 16.5), the new larger Droitwich transmitter adopted the frequency and
the famous Daventry ‘5XX’ call sign, but Daventry was retained, firstly as a
reserve for Droitwich, and later for transmitting coded messages across
Europe during the second world war. The availability and the raw power of
the transmitter during the 1930s also saw Daventry host probably the most
important pre-war experiment ever in the UK, an experiment that laid the
foundations of a technology that more than any other contributed to the
successful outcome of the 1939–45 war, viz, the ‘Chain Home’ (CH) and
‘Chain Home Low’ (CHL) ‘radar’ stations and the airborne radars.
13
372
D. Sheppard