TELE-X - a Satellite System for TV and Data Communication ...

Fig. 5
Block diagram of the payload with its transponder
and antenna systems
Data and video transponders (upper half of the
diagram)
The signal received from the antenna is preamplified
and frequency shifted in one of two
receivers (redundancy). The signals are filtered
and divided between a wideband and a narrowband
transponder. The subsequent amplification
takes place separately at 12 GHz and uses a
common standby channel. The final amplification
takes place in travelling wave tubes of the same
type as the TV tubes and with the same saturation
power, 220 W. However, the operating point used
for the TWTs is approximately 7dB lower than for
the TV tubes, which gives a linear characteristic
with an output power of approximately 45 W.
Additional improvement of the linearity is obtained
by means of amplitude and phase correction
in a linearity unit placed before the final
amplifiers. This is necessary in order to avoid
intermodulation (crosstalk) between the many
carriers in the transponder.
TV transponder (lower half of the diagram)
The incoming signal is amplified and frequency
shifted, and then divided between the three TV
channels 26, 32 and 40 according to the WARC
plan. The final amplification is provided by travelling
wave tubes, which increase the total amplification
to 220 W. Because of the restricted power
supply only two of the three channels are normally
used. All TV, data and video transponder
signals are combined in a filter at the output and
fed out to the common transmit antenna. Like the
separate receive antenna this is a Cassegrain
antenna with a half power lobe width of 1.6x0.8 .
The system also contains a receiver ("RF sensing")
which senses the transmission direction to
the control station on the ground. The antenna
can thereby be directed towards the desired point
and kept to within 0.05 .
Ericsson Radio Systems isthe main supplier
of the FLS station The Finnish
company Valmet OY and the National
Finnish Technical Research Centre supply
the antenna.
The space segment
The TELE-X satellite will be launched by
an ARIANE rocket in February 1987 and
placed in a geostationary orbit at a longitude
of 5 C east.
The satellite consists of two main parts,
the payload and the platform The payload
consists of the communication
equipment on board.
The platform includes functions for propulsion,
attitude and orbit control,
power supply, temperature regulation
and also telemetry and command. The
platform is almost identical to those
used in the German and French TV satellites
TV-SAT and TDF-1. They have all
been produced by the same group of
companies (mainly Aerospatiale and
Thomson-CSF, France, MBB and AEG-
Telefunken, West Germany, and Ericsson
Radio Systems and Saab Space,
Sweden). However, the Swedish share
of the production is much greater in
TELE-X than in the French and German
satellites.
The platform parts are being tested and
space qualified in the French-German
projects, whose time plans are approximately
one year ahead of TELE-X. The
payload is to a great extent new, but as
far as possible it has been based on previous
experience.
FA
D/V-RCVR
IMUX
NB
WB
SW
GCA
TWT
CA
OMUX
TV-BSU
Antenna feeder
Data/Video receiver (with redundancy)
Input filter
Narrow-band channel for 40 MHz
Wideband channel for 85 MHz
Switch
Channel amplifier with linearizer
Travelling wave tube
TV channel amplifier
Output filter
Wide-band preamplifier (with reduncancy)
Fig. 6
The division of traffic between the data and video
channels in TELE-X.
The earth stations are designed so that traffic at
34 Mbit s and 8 Mbit s is transmitted in the wideband
transponder (WBT). WBT is designed to
handle data rates of up to 140Mbit/s.
The 64kbit/s transmission takes place via the
narrow-band transponder (NBT), which can take
500 simultaneous carriers (channels).
2 Mbit/s traffic can be transmitted in either WBT or
NBT. WBT can take 25 channels and NBT 20.
Transmitting 2 Mbit/s traffic via NBT reduces the
number of available 64kbit/s channels. Each
2 Mbit/s carrier occupies the same frequency
bandwidth as 25 different 64kbit/s channels