In the satellite business we
hear people talking about “transceivers” and “BUCs” and we wonder what
they are, and what is their purpose? In fact, these two devices do the
same thing; they are satellite radios that transmit the client’s uplink
data to the satellite.
Transceivers are sometimes called 70 MHz devices, whereas BUCs are
called L-Band devices.
70 MHz Transceivers or L-Band BUCs both do exactly the same thing;
they take the low frequency from the satellite modem and convert it to
either a C-Band or Ku-Band frequency as required by the satellite.
The term L-Band causes a lot of confusion, most people know that
satellites operate in C-Band or in Ku-Band, and now when they hear the
phrase L-Band, they believe that it is yet another standard. It was an
unfortunate name, perhaps the name was the invention of a satellite
engineer who wanted to keep the technology shrouded in mystery and
confusion.
During the previous two years we have been selling a great many
L-Band modems and Block UP Converters (BUCS). Orders for this newer
technology has surpassed sales of the traditional modem and transceiver
package by a factor of four to one; mainly because of price.
A typical VSAT installation has the antenna mounted outside on the
ground, or on a roof, with the transceiver or BUC mounted as close to
the antenna feed as possible. The outdoor equipment is connected to the
indoor satellite modem by a pair of long cables, normally called the IF
cables, one cable handles the transmit data and the other cable carries
the receive signal. If these cables had to carry the original RF
frequency of 4 to 6 GHz they would need to be very thick and very
expensive.
In order to cut down costs, satellite engineers designed transceivers
that would take the high frequencies from the antenna and then convert
them into a much lower frequency. They called this new frequency
“Intermediate Frequency (IF)”. IF frequencies have a huge advantage that
they can be carried over long distances between the antenna and indoor
equipment using cheap cables.
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 data coming from the satellite arrives at a frequency of 4 GHz,
the signal is fed to a LNA or LNC 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 low loss 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.
The transceiver contains all the frequency conversion and
input/output power controls that are needed to send and receive a
satellite signal. It is waterproof and impervious to heat and cold. All
of these features add to the purchase price of the transceiver, which is
typically a combination of four items, a power supply, an SSPA and an up
converter and a down converter.
A typical 20W C-Band Transceiver will cost $16,500 with a comparable
modem costing $3500 and upwards.
In an effort to reduce the price of the transceiver, a new scheme was
developed that uses a higher Intermediate frequency, typically in the
range of 950 to 1450 MHz. 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 BUC power supply, radio output 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
thousand of dollars less than the cost of the older system.
Let’s look at a comparison cost between two sets of equipment, a 20
watt transceiver and modem compared with a 20 watt BUC and L-Band modem,
and then we will do the same thing with a 5 watt configuration.
20 Watt 70 MHz transceiver
Anacom 20 Watt transceiver with LNC $16,650
Datum PSM4900 modem $3,500
Total Price $20,150
20 Watt L-Band BUC
Anacom 20 watt BUC $8,770
PLL LNB $450
Datum PSM-4900L modem $3,930
Total Price $13,150
Conclusion a $7000 saving by switching to L-Band, in fact the
savings can be even higher if we had chosen a BUC manufactured by
another company instead of Anacom |
As a final exercise
let’s look at a similar price comparison between a 5 watt package
5 Watt 70 MHz transceiver
Anacom 5 Watt transceiver with LNC $9,663
Datum PSM4900 modem $3,500
Total Price $13,163
5 Watt L-Band BUC
5 watt BUC $1,770
PLL LNB $450
Datum PSM-4900L modem $3,930
Total Price $6,150
At the 5 watt level, the saving between BUC and transceiver is
$7013. |
