| To illustrate the difference between the
two technologies let me first review the 70 MHz modem and transceiver
combination. I will use C-Band as my example, but everything remains
true for KU band as well. The receive frequency of 4 GHz is collected
by the antenna and fed to an LNA and then passed to the receive port of
the transceiver. Typically the transceiver is mounted on the antenna and
so only a short length of thick cable is required between the LNA and
the transceiver. Once the signal gets to the transceiver it is converted
from high frequency to an Intermediate Frequency (IF) of 70 MHz and then
carried by standard Co-Ax cable the long distances from the antenna to
the indoor equipment. Detailed
VSAT
technical information for Engineers
The transceiver contains all the frequency conversion and
input/output power controls that are needed to send and receive a
satellite signal. It has to be waterproof and impervious to heat and
cold. All of these features add to the purchase price of the
transceiver, which is typically comprised of a power supply, an SSPA, an
up converter and a down converter.
In an effort to reduce the price of the transceiver, a new scheme was
developed that uses a higher Intermediate frequency in the range of 900
to 1100MHz. Even though much higher than 70MHz, this L-Band frequency,
as it was named, can still be carried long distances over cheap cable. |
|
The other change was to replace the
transceiver with a much simpler and cheaper unit called a Block Up
Converter or BUC. The BUC makes a simple frequency conversion and then
acts as an amplifier sending the signal up to the satellite. The BUC is
a very dumb device compared to a transceiver. The power supply, radio
power settings and frequency selections are now moved into the L-Band
modem. The modem sits indoors and does not require the same
environmental protection. The penalty is that the L-Band modem now costs
more than a similar 70 MHz modem. Even so, the cost of the combination
BUC, LNB and L-Band modem is many thousands of dollars less than the
cost of the older transceiver system.
An Anacom or Codan 20 Watt C-Band Transceiver will cost $15,845 and
above, with a matching satellite modem costing $3000 and upwards. A
typical 20W C-Band BUC will cost $7950 with the L-Band modem costing
$3500, at the other end of the scale a 5 watt BUC can cost less than
$2000 compared with the price of an
Anacom 5 watt transceiver at $9663.
As the sales of BUCs continue to increase the manufacturers are
decreasing the prices for their C-Band
and KU band BUCs.
Prices for a KU BUCs are slightly different than for C-Band, but the
same ratio of price savings can be expected.
More considerations regarding L-Band
or 70 MHz for cross site cabling at VSAT installations. |
