ALLISS antenna

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The ALLISS antenna "Volga" was the first ALLISS antenna at the Issoudun broadcasting station in 1993. The facing side shows the low-band antenna.

The ALLISS antenna is a freely rotatable shortwave directional antenna in combination with its own high-performance transmitter with a transmission output power of 500 kW. The name is an artificial word, consisting of the beginnings of the names of the largest French shortwave transmitter locations ALLouis-ISSoudun.

history

This type of antenna was developed in collaboration between Thomson CSF (later Thales ) and TéléDiffusion de France (TDF) as a replacement for the old shortwave transmitters in Issoudun and Allouis . The entire antenna construction is self-supporting, fully rotatable and firmly connected to a transmitter. The result was a compact module, antenna and transmitter in one. The first antenna of this type was put into operation in 1993 after a year of preparation after only six months of construction in the broadcasting center in Issoudun. A total of 12 ALLISS antennas were installed there by 1996. The manufacturer of these antennas was Thales. The transmitters are from Thomson. The antennas at the Issoudun site have all been named after rivers. The names of rivers were used because the antennas let the "(radio) waves flow like water, from one country to another" ( RFI quote , see video of the construction). The first antenna is the "Volga" antenna.

construction

Dipole from Thales (Bj. 94), parts as a round wire trap
Dipole from Ampegon (Bj. 97), completely in tubing

The essential points of the ALLISS system are the integration of the transmitter in the base under the antenna and the use of a rotatable antenna. The entire antenna construction is self-supporting. Neither antenna selector switches nor squint devices or lossy antenna feeds are required. You only need a space of max. 80 m in diameter, a power connection, a (usually) fiber optic connection for the transmission signal and remote control and a water connection for air conditioning the system and cooling the power amplifier. The transmitter with an output of up to 500 kW is located in the antenna's "base". The antenna can be freely rotated through 360 ° in any direction. A full turn takes about 5 minutes. The antenna has two "sides" that are equipped with different antenna systems (high and low band). This means that the entire frequency range from 6 to 26 MHz can be served. In contrast to the curtain antennas that were customary up to now, the antenna has solid dipoles, usually consisting of steel tubes. The reflector walls and the feed lines are made of copper cable or copper pipe. The polarization is horizontal. The newer versions are built in cooperation with Ampegon Antenna Systems GmbH. They can be recognized by the different design of the dipoles. With the first antennas from Thales, the dipoles have one half in the form of a wire trap, with Ampegon the dipoles are completely made of pipe material.

technology

Operational characteristics

With the ALLISS antenna, a transmitter operator is able to freely change all operating parameters at any time:

  • Beam direction from 0 - 359 ° at a speed of approx. 1 ° / sec
  • Transmission frequency and antenna characteristic selection (e.g. HRS 4/4/1 to HRS 2/4/1)

A new transmission destination including a change in frequency and direction can thus be reached within 5 minutes.

variants

RF functional overview of the ALLISS antenna

The two groups of an antenna, front and rear, always physically consist of 4 lines of 4 elements.

Possible variants in the configuration (activation) are:

  • 4 × 4 elements = HRS 4/4 (4 lines of 4 elements on top of each other)
  • 4 × 2 elements = HRS 2/4 (4 lines of 2 elements on top of each other)
  • 2 × 4 elements = HRS 4/2 (2 lines of 4 elements on top of each other)
  • 2 × 2 elements = HRS 2/2 (2 lines of 2 elements on top of each other)

The profit amounts to:

  • Low band (6 - 12 MHz): 11 - 17 dBd
  • High band (13 - 26 MHz): 17 - 21 dBd

Mention should be made of a special ALLISS antenna in Issoudun, the "Gange". It makes a gigantic impression just in terms of appearance. It is the only one of this type that is designed for frequencies from 3,900 kHz (75 m band). Despite the HRS 2/2/1 design (2 × 2 elements, one wave length above the floor) on the low-band side, its dimensions in width and height are almost 100 m. It is used to reach Northwest Africa on 3,965 kHz.

All antennas in Issoudun have groups of 6 × 4 elements (HRS 4/6/1) on the high-band side for an even flatter beam angle. This design is no longer offered today.

Maintenance benefits

All components of the antenna are relatively easy to reach. A fixed ladder with an integrated fall arrest rail is located on the rotatable central mast. The booms contain a playpen with railings (catwalk) and all isolators are easily accessible. No antenna parts need to be dismantled or lowered for maintenance, as is necessary with curtain antennas. The system lifetime is designed for approx. 50 years. The system can be fully remote controlled and monitored. No on-site staff is required in normal operation.

Advantages in construction

All technical components of the system are delivered prefabricated. Once the connections for energy, water and fiber optics have been prepared, the construction of the system, including concrete work, takes about 6 months. This is an advantage that should not be disregarded compared to a conventional system with curtain antennas. An example is the construction of the Wertachtal shortwave transmitter . Here it took almost 3 years to the first minute of broadcast. But then only 4 antennas were available and thus operation was only possible in two directions. The space consumption is also a major advantage: you need approx. 10,000 m² (= 1 ha) per antenna. You can build a module almost anywhere. A station with 15 modules requires 15 hectares of space. In comparison: 200 hectares were required for the Wertachtal radio station.

Web links

Individual evidence

  1. ↑ THALES 2003: THALES Rotable Antenna Array: Home Page. Archived from the original on October 14, 2008 ; accessed on August 6, 2019 .
  2. ↑ THALES 2003: THALES Rotable Antenna Array Design and benefits. Archived from the original on October 14, 2008 ; accessed on August 6, 2019 .
  3. ↑ THALES 2003: THALES Rotable Antenna Array: Technical data. Archived from the original on October 14, 2008 ; accessed on August 6, 2019 .
  4. ↑ THALES 2003: THALES Rotable Antenna Array: Highlights and References. Archived from the original on October 14, 2008 ; accessed on August 6, 2019 .
  5. ↑ Ampegon 2003: Detail of an ALLISS antenna: Catwalk with railings, feed lines and reflector networks. Archived from the original on May 5, 2019 ; accessed on August 6, 2019 .
  6. ↑ Ampegon 2016: Technical data for HP-RCA antennas (ALLISS). Archived from the original on July 30, 2019 ; accessed on August 6, 2019 .
  7. ↑ Ampegon 2003: Detail of an ALLISS antenna: Catwalk with railing and feed line. Archived from the original on August 6, 2019 ; accessed on August 6, 2019 .
  8. ↑ Ampegon 2003: Detail of an ALLISS antenna: symmetrical feed line with isolators. Archived from the original on May 5, 2019 ; accessed on August 6, 2019 .