The B6141 Low Power Self Tuning H.F Broadcasting Transmitter

photo Marconi B 6142 FEATURES


The B 6141 H.F Transmitter is a broadcast version of our highly successful MFT series of self tuning amplifiers. A power tetrode is employed in the output stage.

It is suitable for normal DSB broadcast operation and works in the range 2.3 to 30 MHz. The transmitter will retune automatically to a new frequency in approximately 5s. Nominal load is 50 ohms with a v.s.w.r of not worse than 3:1.

The amplifier employs a wideband solid state input circuit, a tuned penultimate/driver stage and a tuned tetrode output circuit.

Variable elements of the tuning systems are reduced to a minimum and employ only a small number of moving parts in order to maintain exceptional reliability

The control circuits are contained on standard size printed circuit boards and are housed in rack with a simple plug-in arrangement for easy replacement. An extension frame is provided for ease of maintenance. The control system employs solid state techniques, is simple in concept and highly reliable.

Power supply circuits employ air cooled transformers and silicon rectifiers where applicable. Overall cooling is provided by a centrifugal fan and the equipment will operate normally for mains variations from +6% to -10% of nominal.

R.F Data
Power output 7,5 kW
Output impedance 50 omhs unbalanced
VSWR up to 3:1
Frequency range 2.0 to 30 MHz
Frequency changetime autotune 5s maximum
Facility Frequency follow
R.F harmonics Less than 50 mW
Spurious radiation Less than 50 mW
Phase stability Typically 3° r.m.s in 10 ms
Sampling taken 3s or more after frequency change
Frequency standards i) Internal Temperature-Controlled Crystal Oscillator (TCXO), ±1 p.p.m/year, ±1 p.p.m 0°C to 60°C with an internal adjustment capability to take up to 10 years ageing.
ii) With internal standard, 1 part in 108 per day. Less than 1 part in 107 over temperature range -10°C to +55°C. Long term - typically 1.5 parts in 107 per month after one month. Warm up time - 7 min at 20°C for ±5 parts in 108 of nominal or previous setting.
iii) With optional higher stability internal standard, 5 parts in 1010 per day. Less than 1 part in 108 over temperature range -10°C to +55°C. Long term - 1.5 parts in 108 per month. Warm up time - 20 mins at 25°C to within 2 parts in 108 of final frequency.
iv) With external standard, will not derate long term stability characteristics of applied external standard. Standard frequency of 1 MHz at a level of 50 mV to 2.5 V r.m.s in 50 ohms.
Modulation Data
A.F input impedance 600 ohms balanced
A.F input level +6 dBm to -30 dBm
A.F response
Transmitter set to 70% modulation at 400 Hz
±1 dB 60 Hz to 4000 Hz
-1.5 dB 4000 Hz to 5000 Hz
-2 dB 5000 Hz to 6000 Hz
A.F distortion
Over the range 60 Hz to 6000 Hz
At 50% modulation, better than 1.5%
At 90% modulation, better than 2.5%
Noise 55 dB unweighted, below 100% modulation at 400 Hz
Modulation capability 100% continuously (with sinewave 60 Hz to 6000 Hz)
Electrical Data
Power supplies Drive 100-250 V +10% -10% 45 to 65 Hz.
Amplifiers 380-440 V +6% -10% 3 phase 4 wire a.c 50/60 Hz ±2%.
Frequency tolerance ±2 Hz.
Environmental Data
Temperature -10°C to +55°C at sea level
Relative humidity 95% at 40°C at sea level
Temperature range at 2000 m -10°C to +50°C.
for operation above 2000 m a booster fan is required to maintain temperature range.
Mechanical Characteristics
Drive Cabinet Width : 600 mm
Height : 1600 mm
Depth : 700 mm
Amplifier Width : 3000 mm
Height : 1600 mm
Depth : 1000 mm
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
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ITU Country
ITU Country