Moving the earth station antenna

Moving the earth station antenna

In January 2000, AI³ traffic on Ku band has been moved to JCSAT-1B satellite. On this occurence, we had to move the antenna dish in AIT.

Rationale

The satellite JCSAT-1B is located 20 degrees further East than the previous satellite (JCSAT-3) used for AI³ operation.

As a result, the antenna is pointed further to the East and at a lower elevation. On the previous location a building was there that would have been an obstacle to the radio beam. So the antennat had to be relocated to a non-obstructed place.

The movie

This movies summarise the various steps that were acomplished to move the antenna.

Still pictures had been taken every 20 minutes while the work was being done. Edited together, here is the result.

AVI version of this movie is available (40 MB).

Some technical facts

The concrete slab

A 3 x 3 meters, 20 centimeters thick, slab of steel reinforced concrete is used as the base for the antenna. Due to the specific type of the soil, the slab fundation is made of 16 concrete piles, 3 meters long.

To increase the stability, a concrete slab is added that encase the foot of the antenna dish. This second layer of concrete is linked to the base slab with some pieces of steel rod.

Installation of the dish

Four coprer posts, 3 meters long, are used at the four corners of the base slab to provide electrical grounding. Those posts are linked together with 15 sqm copper electrical cable. The antenna foot is grounded this way, as well as every electrical appliances that are used on the outside earth station.

Major problem encountrered was that a missalignment of the antenna panels was creating radio interferences and the signal was degradated. On Ku band, the wavelength of the signal is about 2 centimeters. A missalignment of 5 millimeters represents one quater of the wavelength and cannot be tolerated. After the missalignment was corrected, the normal functionning could be resumed.

Fence

A 2 meters high metalic fence is errected to protect the earth station equipment. Care should be given that the fence is not an obstacle tp the antenna beam.

Given the relatively low elevation (31 degrees) the fence had to be set to follow the exact path of the beam. Here the fence is set with an azimuth of 101.82 degrees East, corresponding to the azimuth of the dish, so the right most part of the fence is parallel to the dish.

The lower part of the figure shows that to escape a 2 meters high obstacle with a 30 degrees angle, the distance to the ground should be 3.40 meters.

Considering that the angle is more than 30 degrees, the distance between the dish and the fence is 4.50 meters and the lower edge of the dish is at 50 centimeters from the ground, enough provision is given so that the fence is non obstrictive.

Monitoring of the link quality shown no modification after the right most side of the fence was erected.