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Repointing on production Hub

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Ex Member
Ex Member


Jul 9th, 2009 at 4:43pm  
Dear All,

I am new in VSAT technology.

I have life IDirect Hub connected to the antenna which is pointing to our existing satt provider. Now, we are thinking to repoint it to other satt provider. We need to do repointing and meanwhile we want to keep the IDirect Hub on life condition.

Any body who can give the best way to do this ?

rgds,

Feldy
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Ex Member
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Reply #1 - Jul 24th, 2009 at 7:57pm  
Hello Feldy

I am presuming you are asking if it is possible to keep your I-Direct system up and running [ with no interruption to the remotes ] whilst moving from one satellite to another.

In short, unfortunately no.

The satellites that we “talk to” using our I-Direct systems are in a “ring or belt” around the earth.

https://www.splung.com/kinematics/images/satellites/geostationary.png


These satellites appear to be stationary as viewed from an observer on the ground. They actually move around a little bit, but I won’t get into that here. Your system has three main components:

1. Your Hub station [ The “Master Controller” ]

2. Your remote sites

3. The satellite itself.

Both your hub station and your remotes all need to be pointing to the same satellite at the same time. When you point your antennas to different satellites you will find that you have to move the position of the antennas with respect to the horizontal [ called azimuth ] and to the vertical [ called elevation ]. There is sometimes an adjustment for a thing called polarization, but we’ll ignore that for just now.

https://www.euclideanspace.com/physics/mechanics/tableTopPhysics/geospatial/aimS...


Many satellites are very close in space to each other [ some are almost on top of each other  in what are called co-located slots ]. Even though they are close, we have to physically move our antennas to get from one to another [ excluding co-location]. The amount by which we move our antennas will generally be different from the hub to the remotes.  This is because the hub and remotes are on different parts of the earth’s surface and the angles which they “look at the satellite” will be different. If we move from one satellite to another, we will “lose signal” when we point into space as we are moving from one to the other. During this period, there will be a complete loss of communications. This cannot be avoided. Both the hub and the remote sites  will have to re-point their antennas. You should be aware that this is not a 5-minute job and depending upon a variety of factors, can take some time. Once you get to the new satellite, you can’t just start service immediately. Tests have to be done with the satellite operator to set power levels etc. When you move from one satellite to the other, you must always stop all transmissions from the hub as these can cause interference to other satellites as your antenna “sweeps across the skies”.

Even though the transmit function on the remotes is normally inhibited from activating unless the receive side is locked, we should always completely physically disconnect transmit cabling from the BUC due to some other technical factors I won’t go into here.

If you have Bill Gate’s money there is a very, very expensive method involving a bunch of duplicate equipment and another hub antenna that could be used which would minimize any interruption, but assuming that the Global Economy hits us all, we will have to make do with a predictable outage.

Having done many satellite pointovers over the years, I can tell you that planning is the key. Step by step instructions on exactly what to do, new pointing angles etc should be sent to all remotes. All antennas should be checked before hand to make sure that all the nuts and bolts to be used in physically moving the antennas are easily moved [ nothing worse during a re-point is to find an old rusty bolt breaks off at the last moment !! ].

One other thing that many people forget is that you may be able to “see” the existing satellite fine at a remote site, but when you move to the new satellite, a building or tree is in the way. Same for the hub [ Even more important, depending on the size and construction of the hub antenna mount, you may not even be able to physically get the antenna to the new position. Planning, planning, planning…

Good Luck
Dave
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Reply #2 - Jul 24th, 2009 at 11:00pm  
Bye the way, as well as having a situation where the hub antenna physically moves to point to another satellite [ which may take some time, depending on the type of antenna , whether motors are installed, whether any of the bearings have seized up from lack of use/lack of lubrication etc ] some hub setups can do what is called an IF switchover. In this case, there is another antenna at the hub station already pointing to the new satellite [ usually with other services already running ]. In this case, the output from the hub chassis [ what we call an IF or intermediate frequency signal ] can be removed from the existing antenna [ and it’s associated electronics – things called “upconverters” and “HPA’s” ] and “attached” to the new antenna [ and associated electronics ]. A similar situation would occur for the receive part of the system.

Depending upon a bunch of factors, this could be done very quickly. No antenna movement is required at the hub. However, the remotes would still have to be re-pointed.

So depending upon the physical configuration of your hub location [ single or multiple antennas etc ], a variety of options may be available. Normally though, it involves physically moving the hub antenna to point to another satellite.

If the hub antenna is a medium size [ say 7.3m or higher ] make sure that the antenna can physically move before the changeover is due.

Things to check:

If no motors are present, do you have hand-bar wheels to move the antenna ? Physically check that they will fit on the spindles.

If you have motors, make sure that they work. Many antennas have been left in the same position for years with no maintenance, and some will “refuse to budge” due to lack of lubrication/rust etc on the moving surfaces which have never been exercised.   A good operator should check the movement of the antenna in azimuth and elevation at least once a year on satellite [ yes, even at Ku-band ] by gently pulsing the motors or hand-barring and using the beacon on a spectrum analyzer to make sure that traffic is not lost. Some of these hub antennas are very heavy, and lack of movement can cause the moving surfaces to “stick together’ or even be “cold-welded” due to lack of lubrication and movement.



Dave
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TDMAMike
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Posts: 826
Reply #3 - Jul 25th, 2009 at 12:32am  
Quote:
Dear All,

I am new in VSAT technology.

I have life IDirect Hub connected to the antenna which is pointing to our existing satt provider. Now, we are thinking to repoint it to other satt provider. We need to do repointing and meanwhile we want to keep the IDirect Hub on life condition.

Any body who can give the best way to do this ?

rgds,

Feldy


1. Are you an HNO with control of the Hub?
2. Do you have another antenna?
3. Are you trying to do this with no downtime or your existing network?  

If you are trying to do a spacecraft swing with one antenna, your networks will incur an extended outage! You will have a service interruption as you cutover to the new freqs (push the remotes) and repoint the antenna. The process is relatively easy, but cutover procedures must be followed closely to ensure that you do not isolate your remotes.  

If you only have a single antenna, you will need to change your freq plans/rates on your existing cards, then push the changes to the remotes (remote side first, followed by the hub side), then apply the freq/rate changes to your line cards (apply the new changes to falcon...thus rolling them over to the new space segment (the remotes will already be on the new freq plans).  Once you push your line cards, start your procedures to repoint the antenna and get an isolation check with controllers.  Once your forward carrier (outroute) is commissioned, your remotes should be waiting on you.  

Lastly, I want to say that if you are NOT experienced in this process, I recommend you hire someone to come in and negotiate it for you. It is a tedious process, that must be followed to the letter.  If you get out of sequence you could potentially strand your remotes and have to email them all a new options file (your FWD carrier is changing, your lifeline will not be there).  Also, you need to ensure that you have done a proper link budget with the new space segment (based on your RFT - Antenna, SSPA/HPA, etc) to ensure you have what it takes to radiate onto that new craft and get the proper signal to noise ratios on the remote end.  A transponder on one craft could be very different on another.

M
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Regards, &&&&M
 
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