Advertisement
FM- 20B FM TRNSMITTER
DZSCRIPTIJN
The FM-20Bis an FM Transmitter with 20,000 watts nominal power
output,
operating on one fixed frequency between 88 and 108 mcs.
The operating characteristics exceed those required by the Federal
Communications Commission for standard FM broadcast service.
The
Transmitter is designed for continuous broadcast oper:Ition and
consists of Exciter Unit,
two intermediate Power Amplifiers and
the Power Amplifier.
Three cabinets are required to house the entire TransLiitter.
The
dimensions are given on the Specific
a
tion Sheet. The left cabi-
net houses two Intermediate Power Amplifiers,
Control Panel, Ex-
citer and the 3,000 volt Power Supply.
The center cabinet houses the Amplifier,
a pair of 40X10,000D
power tetrodes,
the blower and blower controls,
the i-ower Ampli-
fier filament transformer,
and the motor driven variable trans-
former for the driver plate transformer.
The right cabinet houses the control panel,
the 6500 volt plate
supply, the 1500 volt screen supply,
and the bias supply for the
20KW Amplifier.
This cabinet houses all the relay equipment
for starting and stopping the aiaplifier,
and all overload and
protection equipment that pertains to the Power Amplifier.
The M.6095 Exciter,
used in this Transmitter,
employs a phase
shift modulatpr using pulse timing techniques and may be adapted
to single or dual channel Multiplexing on a plug-in basis, with
blank panel space provided for the addition of the Multiplex unit.
Approximately 4 watts are required from the Exciter to drive the
first Intermediate Power Amplifier, which is a pair of 6146's,
which in turn drives a pair of 4-400A's to a kilowatt output.
These in turn drive a pair of 4CX10,000D's to a nominal 20KW
output.
From Exciter output to transmission line at 20,000 watts
there are only three radio frequency stages.
An important feature
of this Transmitter is the lack of frequency multiplication,
after the Exciter.
This helps to eliminate spurious frequencies
and improve tube life.
The driver,
a nominal 1KW unit,
uses a pair of 4-400A power
tetrodes.
The plate circuit consists of a 1/4 wave length
shorted distributed open transmission line.
The plate circuit
is tuned by adjusting a grounded vane which changes the induc-
tance of the plate circuit distributed lines,
and thus the reson-
ant frequency of the plate circuit.
The output of the driver
is coupled into the transmission line by means of an inductively
coupled loop.
Less than 400 watts is usually required from the
driver for a 20KW output from tàe final Amplifier.
6
/
2
2/61
-1-
FM-20B
Advertisement
