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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's first review the 70 MHz modem and
transceiver combination using C-Band as the example,
but everything remains true for a Ku band
installation as well, but the RF Frequencies are much
higher.
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 70
MHz, 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. Most BUCs are dumb
devices compared to a transceiver, but even here
things are changing, with some of the better BUCs you
may connect them to an ethernet feed and program them
from another continent.
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 as an outdoor unit.
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 PSM-505 modem $3,900
Total Price $20,550
20 Watt L-Band BUC
20 watt BUC $6,770
PLL LNB $450
Datum PSM-505L modem $4,230
Total Price $11,450
Conclusion a $9,000 saving by switching
to L-Band.
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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 PSM505 modem $3,900
Total Price $13,563
5 Watt L-Band BUC
5 watt BUC $1,170
PLL LNB $450
Datum PSM-505L modem $4,230
Total Price $5,850
At the 5 watt level, the saving between a
BUC and transceiver is $7,713.
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5 Watt C-Band BUC and 1.8m Prodelin antenna - linear
polarization
5 Watt C-Band BUC and 1.8m Patriot antenna - circular
polarization - note polarizer between the feed horn
and the OMT
Lightweight, small 20 watt C-Band BUC
20 Watt L Band-C band out BUC from Mitec
20 Watt C band Transceiver from Anacom
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