NEC HFB-8047




photo NEC HFB-8047 NEC Corporation (NEC) has led the field in design, development, and manufacture of telecommunications systems and equipments for more than seventy years in Japan. Its experience includes high-power TV, FM and medium-wave broadcasting equipments as well as shortwave transmitting equipment delivered to customers around the world. The performance record of this NEC broadcasting and transmitting equipment has won the acclaim of engineers and technician-experts who judge telecommunications equipment by its proven performance.
This brochure introduces NEC's Type HFB-8047 50 kW Short-Wave Broadcast Transmitter. Featured by its excellent performance, high efficiency and compactness, the Type HFB-8047 occupies less floor space and is superior in performance to any comparable equipment in the world. Its maintenance is extremely simple, and it may be operated as an unattended or standby transmitter due to its extremely stable performance.

All tubes and other circuit components are designed and tested for maximum operational life and efficiency to ensure stable operation.


Only Three Tetrode Tubes in Transmitter.
Three high gain forced-air cooled, tetrode tubes are employed in all, one in the modulated power amplifier, and two in modulator amplifier.

Solid-State RF and AF Driving Stage
Solid-state circuitry is employed except for the power amplifier and modulator. Adopting solid-state circuitry, the driving stage is much compact. All RF solid-state circuits employ a wideband amplifier and requires no tuning circuit.

Extremely Low Maintenance Cost.
High-efficiency electron tubes for HF broadcast use are adopted and the circuit efficiency on the final power amplifier is extremely high thanks to the most suitable variable tuning method.
The tube maintenance cost and power consumption have been greatly reduced by the help of the latest techniques in the application of silicon rectifiers, etc. ...

Solid-State Control Circuit
Auxiliary control circuits components such as auxiliary relays, delay relays, overload relays and 3-shot recycling relays employ IC, ensuring high reliability.

Mimic Diagram
Mimic indicators for the individual circuitx are arranged on the panel in a simplified circuit diagram.
Transmitter's ON-OFF control, pre-set frequencies change control, OLR indicator and metering and waveform monitor at each stage 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, allowing maintenance work to be accomplished wihout hazard.

Unattached or Standby Operation
The transmitter is specifically designed for unattached operation and has all the facilities necessary for interfacing with Remote Control Equipment.

Rated carrier output
(carrier power)
50 kW (up to 9.9 MHz)
45 kW (up to 15.6 MHz)
Frequency range Broadcast bands within 3.2 to 15.6 MHz
Number of preset frequency Up to 6 preset frequencies
Frequency change time Max. 5 minutes
Modulation system Final stage high level plate modulation
Audio frequency response 50 to 7500 Hz, within ±1.0 dB
(relative to 1000 Hz at 50% modulation)
Audio frequency distortion Less than 3% at 95% modulation within a frequency 50 to 7500 Hz
Noise level Better than 55 dB. Unweighted relative to 1000 Hz at 100% modulation
Carrier shift Less than 4% for 100% modulation at 1000 Hz
Carrier frequency stability Within ±10 Hz
Spurious radiation Below 50 mW, complying with CCIR recommendation
Audio input level 0 dBm at 1000 Hz for 100% modulation
Audio input impedance 600 ohms ±15%, balanced
Output impedance 50 ohms, unbalanced
Modulation capability 1000 Hz at 100% modulation: 20 minutes
From 50 to 7500 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 1000 Hz, three times at each interval of 1 second for 2 seconds duration
Power consumption
a) Unmodulated
b) 100% modulation

Approx. 100 kW
Approx. 140 kW
Overall power factor More than 90%
Power supply AC 400 V ±2%
3 phases, 50 Hz or 60 Hz ±2 Hz
Ambient conditions
a) Temperature

From 0° to 45°C
Relative humidity up to 95%
Cooling System of final tubes Forced air
Dimensions (a) Height: 2000 mm
(b) Width: 4000 mm
(c) Depth: 2800 mm
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
1 4CX35,000C 2 4CX20,000B


ITU Country
ITU Country