The antenna alignment refers to the process of adjusting the azimuth, elevation and polarizing angles of antenna to enable the center of beams to point up to the target satellite. It lays the foundation for the earth stations to conduct access validation and daily business transmission. Only through precise alignment of the antenna directed to the target satellite can the work in the earth station become stable and reliable.

The alignment can be done by the users themselves or with the aid of the ground control center of China Satcom.

In terms of the types of antenna, the alignment methods include the following three:

RO station (feedforward or offset antenna) alignment:

TVRO stations or other small DVB data receiver stations often adopt self-alignment. By adjusting the antenna, the signal strength and quality data shown on the digital satellite TV receivers or receiving cards will go to the maximum. Despite simplicity in operation, this method lacks accuracy.

The steps in details are as follows:

1.Obtain the on-site data about longitude and latitude using GPS under the antenna (or adopting the relevant data of the nearest city);

2.Calculate the AZ, EL and POL angles (theoretical values) when the antenna on the site is pointed up to the target satellite；

3．Align the elevation angle of the antenna to the theoretical value using the geological compass or the inclinometer;

4.Connect the LNB to the receiver or receiving card and align it to the required polarizing direction (rough adjustment);

5.Select the signal of TV program or data broadcasting which is known on the targeted satellite and set the center frequency, symbol rate and FECR of the receiver or receiving card as the parameters for the known signal;

6.Adjust the direction of the antenna and lock the receiving signal to make sure that the signal intensity shown on the receiver or receiving card is the strongest and the signal quality is the best;

7.Fix the azimuth, elevation and polarizing angles of the antenna and finish the alignment.

As for selection of the targeted signal, either the broadband signal /TV program on the targeted satellite or the carrier signal transmitted by the host network station, can be used, or ask the operation center of the satellite company to transmit digital TV signal.

Duplex station self-alignment

VSAT duplex stations also make alignment by themselves using the frequency spectrograph to make the received signal of polarized satellite beacons strongest (the reversed polarized beacons’ signal will be swamped in the noise floor).

Ku frequency range has two beacon signals which are orthogonal with each other. C frequency range usually employs the telemeter signal as the reference signal in alignment, which is proven to be more precise.

The steps are detailed as follows:

1.Obtain the on-site data about longitude and latitude using GPS under the antenna (or adopting the relevant data of the nearest city);

2.Calculate the AZ, EL and POL angles (theoretical values) when the antenna on the site is pointed at the target satellite；

3.Adjust the elevation angle of the antenna to the theoretical value using the geological compass or the inclinometer;

4.Rotate the component element of feed source and do rough tuning of POL angle;

5.Slowly rotate the azimuth angle of the antenna in a wide range to search for the beacon signal of the target satellite;

6.The setting of the frequency spectrograph is suggested as follows: REF: –40dBm，5dB/div，ATT: AUTO，CF: frequency of the beacon center，RBW: 10KHz，VBW: 100Hz，SPAN: 500KHz，SWEEP: AUTO；

7.0Hz with the aid of MK→CF. Fine-tune the azimuth and elevation angles to make the signal strongest (at least the main lobe and the first side lobe both on the left and right are visible);

8.Lock the AZ and EL screw rod and rotate the POL angle to maximize the level of the received signal. Record the beacon C/N value for data storage;

9.Change the frequency spectrograph VBW back to 30Hz and SPAN back to 500KHz. The other settings are still the same as the above. Record the beacon C/N value;

Alignment with the guidance of the ground control center of China Satcom

If users do not have the frequency spectrograph, they can make alignments by monitoring the single carrier amplitude transmitted by the surveyed earth station with the help of the ground operation center of China Satcom.

The steps are detailed as follows:

1.Do rough alignment as is described in the Step one to four of the duplex station self-alignment;

2.Transmit the unmodulated single carrier wave (CW) based on the designated power from the frequency point designated by the ground operation center of China Satcom;

3.Guided by the engineer of the ground operation center with China Satcom, fine-tune the azimuth and elevation angle of the antenna to get the strongest signal of the unmodulated single CW into the ground control center;

4.Lock in on the antenna and finish the alignment.

Note:

(1) For the offset antenna of different vendors, their offset angles are different with each other, usually at 15 degree to 25 degree.

(2) The angle of the inclinometer should be the calculated EL angle deducted by the offset angle of the antenna;

(3) If the POL angle is calculated as positive, counterclockwise rotate the main reflective surface directed at the antenna so that feed source is adjusted at a certain angle; If the POL angle is negative, the rotation of the main reflective surface is clockwise;

(4) If there is no polarized signal as needed, adjust the azimuth and elevation angles first via the reversed polarized beacon signal, and then fine-tune the polarized angle to get the strongest working signal.