MARCONI BD 262

GENERAL DESCRIPTION

20 kW HF Air-cooled Broadcasting Transmitter Type BD 262

photo Marconi BD 262

THE 20 kW HF transmitter has been designed primarily for overseas broadcasting duty and is therefore suitable for continuouS operation at full power.

It is an economical transmitter of compact design and pleasing appearance, which combines high-fidelity performance with ease of operation.

FEATURES

Rapid frequency changing by 'push-button' control. The frequency change selector may be mounted anywhere in the transmitter building.

Air-cooled valves are used in all stages with consequent simplification of equipment and reduction in routine maintenance. Should the customer so desire, the heated air may be used to warm the station building.

AC heating of all filaments, eliminating the need of expensive motor generator sets and making possible simple anode and grid current meter and overload trip circuits.

Alternative models are available for continuous coverage of 2.3 to 15 Mc/s, or 4.0 to 27.3 Mc/s.

All major valves have thoriated tungsten filaments having low power consumption and giving linear operation. The low-power valves have oxide-coated filaments.

The transmitter is designed to be suitable for remote control, starting and stopping.

No cable troughs are required in the floor under the transmitter. This considerably simplifies installation and reduces building costs.

The transmitter is divided into small units, facilitating transport and initial installation. The extensive use of aluminium in its construction has reduced handling charges and floor loading to a minimum.

A reliable system of electro-mechanical interlocks ensures complete safety of the operating staff.

Freedom from fire risk. The heavy oil-filled, high voltage components, such as the main rectifier transformer, modulation transformer, and smoothing chokes, etc., can be accommodated in a separate fireproof room if required.

Improved valve design permits the use of moderate HT voltage. This has enabled a high safety factor to be used on the high-power circuits. The characteristics of these valves ensure an exceptionally high anode conversion efficiency.

Valves and all major components are completely protected against damage by accidental overload.

The transmitter is protected against lightning discharge and accidental flashover. It is suitable for operation at any altitude up to 6000 ft.

TECHNICAL SPECIFICATIONS
Power rating	(to aerial feeder): 20 kW at frequencies from 2.3 to 21.45 Mc/s with gradual reduction to 17 kW at 27.5 Mc/s. Capable of 100% modulation
Modulation	High level Class B
Frequency ranges	4-27.5 Mc/s (75-109 m) or alternatively, 2.3-15 Mc/s (130-20 m)
Frequency stability	Normal stability of ±1 part in 100,000. An alternative version of the transmitter is available with an external oscillator, which satisfies the international tolerance figure of ±20 c/s
RF harmonics	Filters are provided to reduce any harmonic to 50 db below the fundamental
AF response	Level within ±1 db between 50 and 5,000 c/s and ±2 db between 30 and 10,000 c/s, measured with reference to 60% modulation at 400 c/s
AF harmonics	Not greater than : 3.5% from 30 to 7500 c/s 2.5% from 100 to 5000 c/s at modulation depths of up to 90%
Noise level	At least 60 db unweighted and 75 db weighted, below 100% modulation
Input level	1 mW into 600 ohm for 100% modulation
Output impedance	193 to 600 ohm balanced or 75 ohm unbalanced. Maximum standing wave ratio 1.4 to 1
Power supply	380-400 V, three-phase, four-wire, 50 c/s AC mains. Voltage regulation ±5%, frequency tolerance ±2%, phase variation within 1% of the mean
Power consumption	Modulation Depth Zero 30% 100%	Input Power 53 kW 59 kW 84 kW	Efficiency 37.8% 35.5% 35.7%
	when modulated at 400 c/s. Power factor 0.85
Dimensions	Height 7 ft (2.1 m)	Width 11 ft 7 in (3.5 m)	Depth 11 ft 8 in (3.5 m)
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
	CYP	CYPRUS	GHA	GHANA
	MWI	MALAWI	NIG	NIGERIA
	AFS	SOUTH AFRICA	SDN	SUDAN
	TZA	TANZANIA