MARCONI B 6123

GENERAL DESCRIPTION

100 kW H.F Broadcasting Transmitter Type B 6123

photo Marconi B 6123

THE B 6123 transmitter embodies techniques designed to provide a small economical high-power h.f transmitter, requiring a minimum of operating personnel. The transmitter, designed to take advantage of 'trapezoidal' modulation, uses vapourcooled valves in the modulated and final r.f stages.

FEATURES

Modulator and final r.f stages vapour cooled.

Wideband r.f circuits facilitates rapid frequency changes. No coil changes required in final amplifier.

Trapezoidal-modulation technique can be employed, with effective increase in range.

Simple installation, transmitter mounts direct on a flat floor.

Self-contained mains distribution for auxiliary supplies. Silicon rectifiers used throughout.

CONSTRUCTION

The transmitter consists of three indoor cubicles and one outdoor enclosure for the oil-filled components. The indoor cubicles occupy a frontage of 16 ft 9 in. (510.6 cm) and depth of 12 ft (366 cm). The modulator and auxiliary power supplies are contained in the left-hand cubicle, the wideband drive in the centre and the r.f amplifier in the right-hand cubicle.

The final stages of the transmitter are vapour cooled and the drive and penultimate stages are air cooled.

CIRCUIT

Simple and rapid change of frequency is possible in this transmitter by the use of wideband r.f circuits. The standard ten-way crystal drive unit, which can be housed in the wideband drive unit, is the Type B 6104. Alternatively, an external synthesizer such as the B 6102 can he used. The drive unit, which employs a distributed amplifier and one tuned stage, is coupled to the final r.f amplifier via a wideband transformer. Both the anode circuit and the feeder coupling circuits of the final r.f amplifier cover the broadcasting bands between 3.2 and 26 Mc/s and are fully adjustable by front-panel controls.

Harmonic radiation is carefully controlled, a reflectometer is fitted, and overcurrent protection is provided.

The modulator, which incorporates negative feedback, also allows for phase correction to compensate for distortion due to clipped sinusoidal input signals when employing trapezoidal modulation. The final r.f stage is modulated via a modulation transformer designed to carry d.c in the secondary winding, thus eliminating the modulation reactor and associated capacitor.

TECHNICAL SPECIFICATIONS
Power output	100 kW carrier at nominal mains voltage
Frequency range	Broadcast bands between 3200 and 26,100 kc/s as defined by ITU regulations, Geneva, 1959
Frequency stability	Better than 5 parts in 10⁶ per month (with B 6104)
Output impedance	300 ohm unbalanced (max. v.s.w.r 2:1)
Drive input	5 W at radiated frequency
Frequency response	±1 dB between 50 and 5000 c/s, ±1.5 dB between 30 and 10,000 c/s, reference 400 c/s, measured at 75% modulation
A.F harmonic distortion	Over range 50 to 10,000 c/s, less than 2.5% at 50% modulation, less than 4% at 9% modulation
Noise and residual modulation	At least 56 dB (unweighted) below level corresponding to 100% modulation by sine-wave signal at 1000 c/s
Power supply	Main h.t rectifier supply adapted to client's requirements. Auxiliary circuits require: 380-440 V (+6% to -10%), 50 c/s (or 60 c/s to order) (±4%) a.c three phase, four wire
Overall power factor	Better than 0.95
Overall power consumption Output (kW) Low band Input (kW) Efficiency (%) High band Input (kW) Efficiency (%)	Carrier 100 172 58.1 182 55	40% sine wave modulation 107 200 53.5 213 50.2	95% trapezoidal modulation 156 290 53.8 310 50.4
Dimensions	Transmitter Width 16 ft 9 in. (510.6 cm) Depth 12 ft (366 cm) Transformer enclosure (outdoor if required) Width 14 ft (427 cm) Depth 12 ft (365 cm)
Specifications may change without notice

TUBE COMPLEMENT
RF stages		AF stages and modulator
Number	Type	Number	Type
?	?	?	?

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	GRC	GREECE	MLA	MALAYSIA
	SNG	SINGAPORE