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Tech Talk
Over the next few issues we are going too explain, in simple terms,
what one of the current buzz words you’ll hear floating around town,
actually is. Yes, were sure you’ve heard it too, VSAT.
A
Dish & Chips
The Ultimate Saucy Solution?
VSAT. What does this actually mean ? What is a VSAT ?
VSAT is an acronym that stands for Very Small Aperture
Terminal. The antenna, or “dish” as it is known, is what
determines if a satellite communication system is a VSAT or not. Any
“dish” 3.8 metres or smaller is technically termed a “VSAT”.
Anything with a dish bigger than this is called an Earth Station.
Typically, a VSAT will have a dish of 1.2 metres, 1.8 metres or 2.4
metres, with 1.2 metres being the most common by far. Some low-end
systems will be equipped with a 1.0 metre or smaller dish and, in
general, these should be avoided.
The dish will be equipped with an LNB, similar to that used by your
DSTV dish, and a small amplifier called a BUC. BUC’s come in various
types, but this is not important. What is important, is the power of
the BUC, and this is vital. The BUC controls how fast you can
transmit back to the satellite or how fast you can “upload” if you
prefer that terminology. For example, pressing the send button in
Outlook Express is actually uploading a file over the internet. If
your computer happens to be connected to a VSAT, then you’re
“Uploading” or transmitting back to the satellite when you press
that send button from your email program such as Outlook Express,
Outlook 2003, Eudora, Thunderbird or MS Exchange amongst others.
The other very important factor in Uploading back to the satellite
is the dish size. The bigger the dish, the stronger the link on the
transmit side of the set up, back to the satellite. We can see then,
how well (read fast) you can Upload back to the satellite is a
combination of BUC power and dish size. You can never have too much
of either!
The BUC/dish combination is the real crux of the issue. If your dish
is too small and/or your BUC is very low powered, you will never get
much beyond 153K/Bits per sec and that is ‘best case scenario’. You
would be well advised to seriously consider your future needs before
you buy into a small 1 watt BUC system with either a 1.0 metre or
even a 1.2 metre dish. This combination will never give adequate
performance, no matter what an enthusiastic salesman might say! This
was a common setup in the early days of VSAT when it cost over 5-6K
for this low end equipment. Time has moved on and inevitably
technology has marched on with it. Today you would not install
anything less then a 2 Watt BUC with a 1.2 metre dish. Of course,
this is not a hard and fast rule. It depends to which satellite you
are Uplinking.
Satellites vary in ability, complexity and age. As older satellites
get replaced by newer satellites, we generally see an increase in
the power of the signal being transmitted by the satellite to the
VSAT. It’s exactly this increase in abilities of the new fleets of
satellites going into orbit that has allowed the current VSAT
revolution.
That’s a simplified overview of course and there are many other
factors to consider. The one you’re most interested in is the
carrier size the BUC/Dish combo can transmit back on. The stronger
the signal, the faster the transmit rate because the stronger signal
allows a much bigger carrier size to be used. The strength of your
transmit signal is the sum total of the BUC/Dish combo and the
strength of the satellite you use. A savvy VSAT dealer will be well
versed in the characteristics of all the “BIRDS” that have a signal
“footprint” over your area. Different satellites are used for
different reasons and the various combinations of BUC/Dish Size and
satellite used will determine just what you can do over a VSAT link.
The correct name for the BUC/LNB/DISH setup is “Outdoor Unit” or ODU.
To conclude for this month, let’s finish up by saying the low end
and slow systems will be using 1 watt BUC’s and dishes 1.0 metre and
smaller and the later high technology systems will be using a 2 or 3
watt BUC and 1.2 metre or 1.8 metre dishes. And as in all things in
life, remember you get what you pay for, so if it’s the cheapest
system on the market you have to ask yourself why. A slow system may
be fine for text based email only, but you will be frustrated if you
do any surfing on the internet beyond the most basic levels. Trying
to upload your photos etc over such low end VSAT’s is an experience
in frustration itself and VoIP (Skype is one type of VoIP) will
never work.
Next Month:
Next month we discuss the IDU or Indoor Unit. The latest technology
systems use satellite “routers” rather then the old outdated
“modems” that the low powered, low end systems use and we will take
a look at why QOS or quality of service is so important. We will
examine systems that use outdated “modem” technology and those that
use the current bleeding edge technology, namely satellite
“routers”. |
February
2006