PSM-2100L Satellite Modem Addendum
Page L-Band - 3
receive must use a subtractive scheme where the IF = 5.15 – RF frequency. This will
result in a spectrum inversion on the receive side only. The receive L-Band IF frequency
is 5150 – 3705 or 1445 MHz.
By having previously entered the BUC and LNB LO frequencies we only had to enter the RF
frequencies. These are the same frequencies that we would see on a spectrum analyzer looking
directly at the station transmit and receive RF.
Notice that these common LO examples resulted in L-Band IF frequencies at opposite ends of the
L-Band range for carriers that were almost next to each other on the satellite.
2.1.1
Some Other Block Converter Schemes
In a single conversion UpConverter from L-Band there is also the possibility of using a “high side”
LO for both C and L-Band transmit frequencies. For a C-Band BUC using a High side LO going
from 950 – 1450 MHz to 5925 – 6425 MHZ the LO frequency would be 7375 MHz (950 + 6425
MHz). There would be an inversion in the transmit output spectrum. Notice also that the highest
transmit output frequence results from using the lowest L-Band modem transmit frequency.
The same schemes are possible at Ku-Band frequencies, where either a high or low side LO may
be used. The following table summarizes the straightforward low and high side LO frequencies for
Block Up and Down Converters.
Band
Up/Down
Freq Range
(MHz)
LO
LO Freq.
(MHz)
Spectrum
Inversion
Notes
C
Up
5925-6425
Low
4900
No
Common
C
Up
5925-6425
High
7375
Yes
C
Up
5850-6350
High
7300
Yes
Brazilian
C
Down
3700-4200
High
5150
Yes
Common
C
Down
3700-4200
Low
2750
Yes
Not used
Ku
Up
14,000-14,500
High
15,450
Yes
Ku
Up
14,000-14,500
Low
13,050
No
Ku
Down
11,700-12,200
Low
10,750
No
Common
Ku
Down
11,700-12,200
High
13,150
Yes
?
Of course there are many possible frequency ranges used for satellite stations in different parts of
the world and we make no attempt to show them all here. This table is simply to list some of the
possibilities. The PSM-2100L tunes over more than the typical 500 MHz (700 MHz), so it is also
possible to use an LO frequency that allows a single modem and Converter to cover multiple
frequency ranges. For example, a 4800 MHz C-Band Low side LO would translate the 950 to
1650 MHz range (available in the PSM-2100) to 5750 to 6450 MHz.
2.2
Transmit Output Power Levels
The PSM-2100L has increased the range of power levels available from the transmit output. This
is to accommodate direct connection (through a bias T mux) to a standard BUC including
significant cable loss without the need for inline amplifiers or attenuators. The PSM-2100L can
output from –35 dBm to +5 dBm in 0.1 dB steps. This 40 dB range can accommodate a wide
range of cable length and BUC gain. Assuming for example that with a BUC gain of 50 dB, and a
4 Watt maximum output (+36 dBm) the required BUC input to achieve full output power would be
–14 dBm. The modem then could drive up to a maximum of 19 dB of cable/connection losses.
This could be a maximum of 100 to 400 feet or more depending on the size and type of cable