Tech Talk

In our final look at VSAT and what it actually is and how it works we are going to discuss satellite footprints and the UPLINK teleport and why this is important.

Satellites are in geosynchronous orbit with the earth. This means the satellites rotate at exactly the same speed as the earth and are therefore always in the same spot relative to earth. This is a crucial aspect to how satellites work. Imagine setting up your dish today and aiming it at a given satellite, only to have re-aim it tomorrow because the satellite has moved! Not good!

All geosynchronous satellites are located around the equator in a location called the “Clarke Belt”. The Clarke belt is exactly 22,366 miles (35,786 Km) above the surface of the earth. This means a satellite can only “see” a certain part of the earth’s surface. It is this part of the earth that a satellite can “see” that is the footprint. Different satellites can see different parts of earth. Therefore when you want VSAT service, you have to aim your dish at a satellite that has a footprint over your location. Pretty simple so far, right?

Well, it gets more complicated as we dig deeper into finding a satellite for our VSAT we want to use. Not all satellites are created equal. It’s fair to say that later model satellites have far more power then a satellite that may have been launched 5 or 6 years ago. This matters to you because the more power the satellite has the smaller the dish and BUC you can use to receive Internet at a given bit rate. (you do remember what a BUC is from previous instalments don’t you?) A smaller dish and BUC directly translates into reduced cost for your VSAT equipment. But wait, there more. A crucial part of selecting the right satellite is consideration of where the UPLINKING facilities or teleport is located. This is very important on KU band for reasons we will explain.

Because KU band is in the 11-14 Ghz frequency range, it is very susceptible to rain or other inclement weather. If the teleport that UPLINKS to the satellite is covered by a heavy downpour of rain, the signal is attenuated or degraded to such an extent that the signal UP to the satellite is almost cut off. Worse still are snow storms. This means if the teleport that UPLINKS to the satellite you are using for your VSAT is in a location that gets heavy snow, you WILL get cuts to your service when it snows at the teleport location.

The map below shows a footprint of the KU band W3a satellite. This satellite has perfect coverage of Zambia and surrounding countries. The area inside the inner dotted line provides the strongest signal. As you go out to the next dotted line the signal gets weaker. It can be seen that Southern Africa is well covered and it’s only West Africa that may have to use a big dish and BUC to get a fast bit rate.

So W3a might be considered a perfect satellite or “bird” as it is called in the trade, for Africa. Well its not quite, but you knew that was coming didn’t you? Sorry for that. The problem with W3a is that the UPLINK teleport is located in Turin, Northern Italy. Turin is at the foot of the Italian Alps. The Alps are very popular as a skiing destination because it gets so much SNOW! Every northern winter we get service disruptions on the W3a service because of snow storms rolling in off the Alps. Something to think about when that slick salesman in shiny shoes is trying hard to convince you to sign up for a VSAT service running on W3a. Don’t get me wrong, W3a is a fine satellite and works extremely well but it does get cuts to service when it snows in the Italian Alps.

An alternative to W3a is PAS10. This is the same satellite that provides service for DSTV. See the footprint map below.

There are quite a few different UPLINK teleports to the PAS10 satellite. One of the better ones is in Amsterdam. The great thing about Amsterdam is it hardly ever snows there! Ah, but wait there’s more! There are two KU band spot beams over Africa on PAS10 and you need to make sure you get the right one. If you compare the footprint map below to the footprint map above you will see the different contours over Zambia and this has major implications to the size dish and BUC you will need, depending on where in Zambia you are located. Make sure you get the right advice if you are going to use PAS10.

The unfortunate thing about KU band service is that there are only two satellites that can provide KU band VSAT service over Southern Africa. Little real competition on KU band means higher prices.

The C Band Alternative

In stark contrast to KU band, C band coverage over Africa is plentiful. There is no shortage of suppliers who can provide a good solid service to your VSAT on C band. One of the better C band satellites is AMC12. The AMC12 satellite was launched in 2005 and has been designed for IP operations. This means the satellite is optimised for IP traffic such as Internet and VoIP (Skype) and is one of the most powerful satellites in orbit today.

One of the major advantages of using AMC12 is the UPLINK to the satellite runs out of Cyprus. The major advantage to this is Cyprus has little rain, NO SNOW, and does not suffer from sandstorms that are found in the Middle East. Cyprus has major fibre optic links to London straight into the Internet backbone. Cyprus is probably one of the best spots on earth from which to have UPLINK facilities. AMC12 comes highly recommended. Another of the premier C band satellites is NSS7. This satellite is also very high powered meaning you can use a smaller dish and BUC while getting very fast connection speeds, especially on the uplink from the VSAT. The only real problem with NSS7 is that this “bird” is full and thus it is very expensive to get space on any of its transponders.

There are many different C band satellites over Africa. Thus you can often get some very good value deals for bandwidth on C band. Of course the other major advantage of C band is that it does not suffer from rain “fade” to anywhere near the same extent that Ku band does. This combined with the great prices on offer out there mean you should really be looking for C band equipment when you are shopping for a VSAT.

Conclusion

We hope you have enjoyed our series on VSAT and what some of the terms and acronyms surrounding VSAT mean. The main points to be remembered are that C band provides the best quality service and in general the best deals are found on C band satellites. Ku band suffers very badly from rain “fade” so this should be taken into account if you want to use a VSAT for business activities. QOS support is what you should be looking for when shopping for equipment and that satellite “Routers” are vastly superior to old outdated “modems”.

Probably the best value for money setup in Africa today is an iDirect 3100 series satellite router that features QOS, coupled to a 1.8 metre dish using a 5 watt BUC and LNB, aimed at AMC12. This setup is industrial strength, very reliable and excellent value for money. This is as good as it gets with VSAT in Africa today.

In Zambia you can get a VSAT from ;

Zamnet 01-225358

CopperNet 01-223333

Pronet 01-228969

Africonnect 01-232005

Microlink 01-222793

Precision Electronics 01-228274

Real Time 01-237771

Evolution 01-227171

African VSAT Systems 01-223608

VSAT information kindly supplied by Heather Bender from African VSAT Systems.