NEC HFB-7840

GENERAL DESCRIPTION

TYPE HFB-7840 10 kW SHORT-WAVE BROADCAST TRANSMITTER

GENERAL

photo NEC HFB-7840

NEC Corporation one of the largest communication equipment manufacturing companies in Japan, can claim to hold unequalled experience in development, design and manufacturing of all kinds of radio and wire communication equipment.

As for large-capacity radio equipment, in particular, NEC has a brilliant record in the manufacture of high power communication equipment in various fields, such as in TV broadcasting equipment, in FM broadcasting equipment, in medium wave broadcasting equipment, and in short wave transmitting equipment.

For exellent performance and operating records of the above listed equipment, NEC has established an exceptionally high reputation among communication engineers and customers, both in Japan and abroad. With a combined record of excellent performance and stability, in combination with rational design, extremely compact sizes, and high efficiency, NEC transmitting equipment are superior to any known contemporary products manufactured by any other companies.

These features have favorable influence not only on the equipment itself, but also upon the economy of station structure and the selection of site areas as well as low maintenance costs of equipment. Also, NEC transmitting tubes used in NEC transmitters have won admiration from here customers for their record of long life.

This high reputation comes not only from excellent transmitting tube design itself, but also from the rational design of the transmitters.

FEATURES

Only Three Tetrode Tubes in Transmitter
Three high gain tetrode tube are employed in all, one in modulated power amplifier and two in modulator amplifier.

All Circuits of Solid-State except PA and MOD
With use of solid-state circuits, driving stage has been improved in compactness.

Extremely Low Maintenance Cost
The high efficient and the most suitable electron tubes for HF broadcast have been adopted and circuit efficiency on the final power amplifier is very high owing to the variable tuning method.
Tube maintenance costs and power consumption has been extremely reduced with the help of the latest techniques of using silicon rectifiers, and so on.

Reduction in Installation Costs.
In designing the present transmitters, HT parts as modulation transformer, choke, anode transformer, etc. were thoroughly investigated and made as compact and light-weight as possible by the most rational design possible, and further, tubes and parts could be most rationally disposed due to the reduction in size and weight of both the final stage power amplifier tubes and the modulating tube.
This resulted in the incorporation of these HT part, including the motor-driven blower inside the transmitter proper.
This has resulted in an epoch-making reduction of the effective area occupied by the equipment, and requires no necessity for work incidental to the building structure, such as wiring ducts, air duct, guard railing, etc., and moreover a remarkable reduction in the construction cost of the transmitter station structure.
As a result of this reduction in power consumption, mentioned above, the capacity of power receiving and distributing facilities could be lessened considerably.
Therefore, costs required for construction of the station structure, for accessory equipment, and for installation work could be economized to a large extent as compared with those of conventional system.

Top-Grade Performance
Performance of this transmitter meets not only specifications related to the international telecommunication acts and the Japan Radio Wave Low, but also any to level performance required anywhere in the world for these types of units.

Capable of Unattended Operation
In addition to the rational design, sufficient consideration has been made, in particular, for reliability of operation.
This is secured by the longevity of the tubes, combined with most appropriate usage and disposition of selected parts.
Thus, by annexing suitable automatic equipment, such as a relay clock, a remote-control device, etc. to the transmitter, stable and reliable operation of this transmitter of unattended station is practicable.

Ease of Maintenance and Inspection
Panels and parts are most rationally disposed with utmost care. Operation of essential parts to be supervised in routine maintenance service may be checked on meters without any hazards due to accidental contact to HT parts.
On the face of the front panel are various measuring instruments, transmitter starting switch for your easy maintenance, daily and periodically.

Complete Protection of Equipment and Personnel
To provide complete protection for the equipment and personnel, this transmitter incorporates all necessary protective relays and an interlocking device that enables it to be started only in a prescribed sequence. In addition, the safety devices, which are used to completely protect the operator from the danger of contacting HT parts, are designed in accordance with appropriate domestic and internationally sanctioned codes and methods.

IC Control Circuit
All auxiliary circuits such as auxiliary relay, delay relay, overload relay and recycling relay except heavy duty magnetic contactor are of integral circuit, they thereby achieve to promote reliability considerably because of the following improvements:
- less mechanical abrasion
- less heat radiation
- free from environmental influence such as dust and various poisonous gas.

Mimic Diagram
Indicators relating to each circuit are arranged on the panel printed by the simplified circuit diagram. Prevision has been made to facilitate identification of tuning push buttons for particular stage of tuning.
Transmitter's ON-OFF control, pre-set frequencies change control, OLR indicator and waveform monitor are all collected on this panel so that the transmitter can be operated, adjusted and checked with ease.

Mechanical Interlock
Mechanical interlock is provided to prevent the door from being opened by a key when HT is applied.
Also, opening the door will mechanically ground HT, hence maintenance work can be accomplished without the danger of HT.

TECHNICAL SPECIFICATIONS
Rated output (carrier power)	10 kW
Frequency range	3.2 to 15.6 MHz
Frequency change	6 pre-set frequencies
Frequency change time	Max. 5 minutes
Modulation system	Final stage high level plate modulation
Audio frequency response	From 50 to 7,500 Hz, within ±1 dB From 30 to 10,000 Hz, within ±1.5 dB (reference level 50% modulation at 1000 Hz)
Audio frequency distortion	Less than 3% at 95% modulation within a frequency range from 50 to 7,500 Hz
Noise level	Better than 60 dB. Unweighted for 1,000 Hz at 100% modulation
Carrier shift	Less than 3% for 100% modulation at 1000 Hz
Carrier frequency stability	Within ± 1 x 10^-6
Spurious radiation	Below 50 mW, complying with CCIR Recommendation
Audio input level	0 dBm, 1,000 Hz, 100% modulation
Audio input impedance	600 ohms ±15%, balanced
Output impedance	50 ohms, unbalanced
Modulation capabilities	1,000 Hz at 100% modulation: 20 minutes From 50 to 7,500 Hz at 100% modulation: 10 minutes Overmodulation: Can withstand a level three times as high as the input level, required to achieve 100% modulation at 1,000 Hz three times at each interval of 1 second for 2 seconds duration
Power consumption	(a) Unmodulated: approx. 24 kW (b) 100% modulation: approx. 33 kW
Overall power factor	More than 90%
Power supply	AC 400 V ±2%, 3-phase, 50 or 60 Hz
Ambient conditions	(a) Temperature: 0°C to 45°C (b) Humidity: Relative humidity up to 95% (c) Altitude: Up to 1000 m above sea level
Dimensions	(a) Width: Approx. 2,000 mm (b) Height: Approx. 2,000 mm (c) Depth: Approx. 1,000 mm
Weight	Approx. 2,000 kg
Specifications may change without notice

TUBE COMPLEMENT
RF stages		AF stages and modulator
Number	Type	Number	Type
1	4CX15,000A	2	4CX5000A

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	IND	INDIA	INS	INDONESIA
	J	JAPAN	KOR	KOREA SOUTH
	MHL	MARSHALL ISLANDS	MNG	MONGOLIA
	BRM	MYANMAR	NIG	NIGERIA
	PNG	PAPUA NEW GUINEA	THA	THAILAND
	UGA	UGANDA