Help on installing Beacon Receiver and ACU

Sir we are installing ASC300LW beacon receiver and VERTEX  7200 ACU on our antenna  system. The ACU is installed already but we are controlling the antenna manually. We wanted to integrate our newly acquired beacon receiver to the ACU to auto track our satellite. No one in the office is experienced on installing this. Am I correct that we have to set the ACU on step tracking mode?

Sir I started configuring the beacon receiver what frequency is it requiring? I taught it needed the L-Band frequency but when I input our L-Band frequency it does not lock the signal.

Sir I was able to lock the signal but I'm having a low DC voltage even my attenuation level is set to 0dB. My reading is only 5.4VDC. What does this imply?

Thankyou sir! I'll try to retrack our antenna.

ok sir I will return to you as soon we have some improvements. Thanks

I'm not sure what you mean by beacon instability.

If the level gradually declines over say 10 minutes and then is increased to a higher level following a step track peak up sequence then that is normal. During the step track peak up sequence there will be several step changes in the beacon level as the controller explores small movements in different pointing directions.

During rain the beacon level will vary.  If your intelligent step track has had enough time to learn the daily orbit movement then then the tracking may go to orbit prediction mode during the rain fade.

It is most unlikely that the satellite beacon itself is varying in level - unless you are using a "beacon" that is actually an uplink CW carrier from another earth station.

Monitor the beacon level with a spectrum analyser. Note that if the frequency drifts due to LNB LO temperature and you are using a narrow filter bandwidth this will cause the level to drop. Be alert to this possibility; it applies to both beacon receivers and spectrum analyers.

If you are operating at low elevation angle (under 10 deg at Ku band or under 5 deg at C band) your signals will vary significantly in level due to scintillation.  This involves both upwards and downwards level variations due to refraction effects in the atmosphere. It is the same phenomenon as the twinkling of a star near the horizon. Scintillation occurs for long periods of many hours. In humid conditions scintillation may be observed, to a lesser degree at higher elevation angles, up to 30 deg elevation.


This graph shows +/-3 dB variation in beacon level at Ku band over one hour at 5.4 deg elevation. Operation of Ku band above 10 deg elevation is recommended.

Faults can cause beacon level variation. Consider loose connectors, DC supply voltages, interference, antenna or subreflector moving in the wind, birds/insects on/in the feed etc.

Best regards, Eric.

A 6V change and a scale of 0.5V per dB means that the beacon receiver output shows a change of 12 dB over 24 hour period. Was the change gradual and always in same direction or was it quasi-sinusoidal ?  Plot the level on a graph every hour for a couple of days. Does the level vary with satellite's position in its orbit ?  Does the level vary with your LNB temperature ?

Some ideas to try:

Do the levels of all the carriers on the satellite also change simultaneously over a range of 12 dB ? What variations do you measure with a spectrum analyser ?  If all change the same way then maybe your dish is not pointed at the satellite all of the time, like this:

In this example the maximum signal will occur once per day when the satellite approaches close to the beam peak.

Does adjusting the frequency tuning of the beacon receiver make any difference ? In which case maybe the LNB LO is drifting with temperature. Do you have a PLL LNB, preferably with external 10 MHz reference ?

Does manually repeaking the pointing of the dish every hour make any difference ?  The main beam of the antenna has a pointed shape with steep sides and rounded top.  If your dish is fixed, the satellite will move about across the beam pattern and the level will vary, with the pattern approximately repeating every day.  The satellite moves in an ellipse or figure of eight pattern and depending on where is the centre of this pattern relative to your beam centre you will see a variety of quasi-sinusoidal level variations with one or more peaks and troughs over the course of a day.  

Best regards, Eric.

Hello,

Yes, it is possible. where is the dish located and on which satellite?

To set the polarisation do it manually. Call the satellite NOC and they will ask you to transmit a low level CW carrier on some suitable safe frequency.  They will measure the x-pol level and talk you into the deep null as you rotate the feed in 1 deg (or less steps) around the correct position.   Accuracy of +/- 1 deg is required and the deep null can best be observed on at the satellite NOC teleport spectrum analyser. Record the final position for future reference.

While you are not correctly aligned in polarisation your transmit carrier is interfering with other users of the satellite on the opposite polarisation.

Best regards, Eric.

The ACU will probably have a number of satellites pre-configured in its menu.

Each satellite will have a polarisation angle pre-set so when you "go to" a satellite it will set the polarisation up appropriately.

Once you have manually measured the polarisation angle for a particular satellite it should be possible to edit the antenna satellite record to match the manually measured polarisation angle.

The ACU can't 'peak up' on polarisation using the co-pol beacon level as the maximum is much too broad. My guess is that the polarisation is set from a manual data entry or "save current satellite" command.

Best regards, Eric.

If you have a spare beacon receiver with which to compare, it would help isolate the issue to either the receiver or the rain.

I say that because I've controlled large terminals (up to 18m) in the Philippines myself, and even they'd lose auto-track regularly during rainy season. It was common practice to set the beacon alarm several dB above threshold so that we knew to run over to the console and start manually tracking until the rain passed. Sometimes the rain would completely attenuate the signal, despite our best efforts at manual tracking. When that happened, we just locked the brakes and waited it out. Once that particular cloudburst diminished enough to re-acquire, we'd flip back to auto-track and go about our business.

//greg//