U S E R R E P O R T

The new Saentis antenna tower

Kathrein antenna systems designed for use at high altitudes

Mr Christian Rebetez, Network Consultant, Broadcasting and Mr Samuel Pache, Network Consultant, Network Buildings of SWISSCOM report about the problems encountered when a transmitter location is also a tourist attraction.

The Saentis mountain with a height of 2,500 m above sea-level is part of an imposing mountain range south of Lake Constance and near to the well-known Swiss town of Appenzell. It is a popular destination for tourists, many of whom use the cable-car to get up to the top of the mountain. Since 1955 Saentis has served us as the location of a transmitter for television and radio channels of the Swiss TV company, SRG, as well as providing a number of mobile communication services.

Saentis is a very important transmitter site for us, but due to its location at the northern edge of the Alps, its peak has a climate similar to that of a mountain 3,500 m high. During and also after periods of bad weather, the danger of being hit by ice falling off the old transmitting tower was especially perilous for the visitor terraces located immediately next to it. The visitor terraces had to be cordoned off for up to 100 days per year, including many summer days when there were countless visitors around.

The Saentis cable-car company therefore demanded that appropriate action had to be taken to eliminate the danger to tourists as a result of ice falling off the transmitting tower. Swisscom then had the following options:

• To set up a completely different site and give up the Saentis location.
• To install a new transmitting tower on top of Saentis which posed no further problems for visitors regarding ice formation.

Since we could find no suitable alternative location for this transmitter, we decided to construct an entirely new transmitting tower at the top of Saentis. The most important factor was to stop ice from falling off the tower when tourists were on the visitor terraces. Furthermore, as low a wind-load as possible had to be achieved for the tower. The radiating characteristics of the old antenna systems had to be main-tained or modified according to the customers' requirements. The solution to these problems was to design a wholly enclosed antenna support with no horizontal outer surfaces (in order to avoid the accumulation of ice and snow) and which was of various diameters to suit all the antenna systems installed. Moreover, a special heating system had to be designed and installed in the radome.

The antenna supplier chosen for this Saentis project had to have the competence and experience to be able to supply all the antenna systems and to be able to integrate them in the special radome. In order to guarantee the functioning of the antennas behind the radome, the supplier had to assume responsibility for this whole part of the project. The reliability of all suppliers was a very important factor in ensuring trouble-free installation, so that the extremely tight time-schedule - which could still be considerably influenced by the unpredictable weather - was not endangered.

Out of a number of possible candidates we selected the company KATHREIN-Werke KG from Rosenheim (Germany) to plan, project and implement the antenna systems and the outer radome. Kathrein had already worked as an antenna system supplier in partnership with Swisscom on other major projects for the transmitters at the St. Chrischona (Basel), Uetliberg (Zurich), Chasseral (Neuchâtel), Bantiger (Bern) and Rigi (Luzern) sites.

We assigned the projection and the execution planning of all the steel works to the Swiss company, Hitz and Partner, who had already proved their reliability with earlier projects.

In the Spring of 1996 work was begun on the installation of the new tower. In spite of many breaks in the work due to bad weather, the schedule for the installation works was kept to or even improved upon in many cases. In November 1997 we put the new antenna systems into operation.

The new tower is 124 m tall and up to a height of 84 m it is constructed as a steel carrier with an outer GRP radome. The upper part is a self-supporting GRP con-struction, manufactured by Kathrein's sub-supplier, IBK.

The following Kathrein antenna systems are installed on the tower:

The GRP radomes also supplied by Kathrein can be heated sectorially to free the tower of ice and snow. The heating elements are controlled from the transmitting control centre and can be switched on according to the required time of day, length of time, number of elements and also their exact position. Thus precise de-icing of the tower radomes is possible before the first tourists arrive at about 10.00 a.m. in the morning by cable-car.

Our new transmitting system has now been in operation for one year without any operational problems occurring. Our requirements concerning keeping the tower free of ice and trouble-free operating of the antennas have all been fully met.