Site: NHK (Japan Broadcasting Corp.)
Science and Technical Research Laboratories
1-10-11, Kinuta, Setagaya-Ku
Tokyo 157, Japan
Date Visited: October 20, 1992
Report Author: E. Miller
NHK is Japan's public broadcaster and is supported by monthly receiver fees of 1,370 yen for terrestrial broadcasts and an additional 930 yen for satellite broadcasts. In 1992, the NHK budget was 513 billion yen. There are more than six million satellite receivers, and in 1991, two 24-hour satellite channels were being broadcast by NHK.
The NHK Science and Technical Research Laboratories (S&T) has a 8.4 billion yen annual budget. The staff of 310 persons includes 270 research scientists. About 10 to 15 persons at S&T are doing satellite-related work. The S&T Laboratory has no separate satellite division. Broadcast satellite work is done in the Radio Engineering Research Division and the Digital Broadcasting Systems Research Division.
In 1989, NHK initiated 24-hour BS services, providing two channels via the BS-2a and BS-2b satellites, launched in 1984 and 1986, respectively. Satellites BS-3a and BS-3b were launched in 1990 and 1991. NHK shares the satellites with JSB, a commercial broadcaster operating a 24-hour satellite channel and TAO, Telecommunications Advancement Organization. NHK and JSB entrust satellite control to TAO.
NHK has supported the development of TWTs for space use. Their in-house capabilities include modeling, design, and test. They have developed a three-dimensional beam modeling program. The tubes are built by outside manufacturers, NEC and Toshiba. Developed tubes displayed are listed in Table NHK.1. These tubes were built for use on future broadcast satellites. Metal-coated cathodes are used (Morishita 1991; Yamamoto 1991).
NHK has developed a Ku-band SSPA with an output power of 40 W.
NHK has developed output multiplexers for broadcast satellite use. Equipment shown included an eight-channel, 200 W/channel multiplexer with 0.7 dB insertion loss; a four-channel multiplexer, capable of carrying 400 W/channel, with 0.5 dB insertion loss; and a 4-channel input multiplexer using an eight-pole elliptic-function filter design, all operating at 12 GHz (Nomoto 1984).
A picture of a 22 GHz breadboard broadcast satellite transponder was shown. A variable EIRP transponder concept was presented. A combination of TWTA power level changes and switching in an additional TWTA is used to provide a power range of 60 to 320 W.
A unique shaped-beam antenna was shown. The antenna radiation pattern has a contour which matches, more closely than an elliptical beam, the shape of the Japanese island archipelago (see Figure NHK.1). The antenna has a reflector surface shaped by "level changes" (as on a contour representation of a ridge). A picture does not show these level changes well, and in practice, the transitions between levels are made smoothly and do not show at all. The subreflector (when used) is also shaped to achieve the desired contour. These surface-shaped reflectors, when illuminated by the single circular, corrugated horn, produce the contour shown. The innovation was to achieve this relatively complex contour using only a single feed (Shogen 1992a, 1992b).
NHK Developed Tubes
Figure NHK.1. Beam Coverage Using Shaped Reflector
Mobile BSS receivers have been developed for use on trains, buses, and automobiles, with each being progressively smaller and lighter in weight (Takano 1992).
A magnetostatic wave filter component has been developed which enhances the signal-to-noise ratio in broadcast receivers. The device operates on the principle that small signals (noise) have a greater transmission loss through the device than do larger signals (the wanted signal). The enhancer improved the S/N by about 8 dB for low C/N (approx. 2 dB). At a C/N near 12 dB, the device provides only about 1 dB improvement. The most effective applications would be beyond the normal coverage area or to improve performance during rain fades. The enhancer is a small, passive circuit using magnetically biased YIG filters (see Figures NHK.2 and NHK.3) (Nomoto and Matsushita 1992).
A system designated as ISDB (Integrated Services Digital Broadcasting) was described as a broadcast system which integrates various kinds of broadcast services such as TV, HDTV, sound, data, etc. as a whole and transmits their signals by making the most of digital processing and digital modulation technologies. NHK demonstrated the ISDB system for the visiting NASA/NSF panel, operating within a single satellite channel, combined high quality sound with HDTV still images to provide a high quality audio-visual program (Kawai 1992; Hamada).
For BSS-sound, systems were described that transmit, using PCM, 6 or 12 high quality, stereo sound channels through a single satellite transponder channel (Kawai 1988).
In television coding, a 135 Mbits/sec HDTV codec was shown. Also, MUSE-TV signals have been digitally encoded at 60 Mbits/sec (Ohtsuka 1992; NHK Hi-Vision Fact Sheet).
Hi-Vision, an HDTV standard developed by NHK, is being satellite broadcast via BS-3b for eight hours per day, using the analog MUSE transmission system, to more than 300 public sites and 10,000 individual receivers.
BSS experiments on future DAB for mobile reception and studio-quality HDTV broadcasting are planned using the ETS-VI and COMETS spacecraft making use of 2.5 GHz transponders and 21 GHz 200 W TWTAs, respectively.
NHK is focussed on broadcasting. Funding is assured through monthly fees on every receiver. NHK provides a unified, stable, long-term outlook for broadcasting satellite development. There is no corresponding entity in the United States. They have a technology development program and an overall program plan that has provided progression from conventional BSS-TV at Ku-band, to HDTV broadcast at Ku-band, and continuing through to possible DBS TV at 21 GHz.
The NHK approach to BSS is the classical approach in a mass market, that is to put the high power and higher cost at the single unit (the spacecraft) in order to reduce the cost of the mass quantity units (the BSS receivers). Europe and the U.S. have chosen lower power/channel for their BSS services.
Figure NHK.2. Configuration of the MSSW Filter
Figure NHK.3. Block Diagram of the Signal-to-Noise Enhancer