L-Band IF Application Guide
Page L-Band - 6
DTE
O
M
T
UC/PA
"BUC"
LNB
Bias T / MUX
Bias T / MUX
F
F
N
LMR-400 (25 - 200 ft)
10 MHz OCXO
Reference
24V
DC
RG6 (25 - 200 ft)
13/18 V
DC
N
Typical VSAT Configuration
L-Band Version
MAB 8/12/02
DIN
Transmit IF
Receive IF
M5 L-Band Modem
This is not intended as a definitive guide to design of L-Band stations. Rather it is a list of
considerations and recommendations when putting together the equipment complement for a
station. Note also that the BUC and LNB usually require power and reference signals. The
voltages show on the diagram above are dependant on the particular equipment used. Some
BUCs require approximately 15 volts while others may use approximately 36 or 48 volts. Some
BUCs also use a reference frequency in the L-Band range instead of the more common 10 MHz.
3.1 Block
UpConverter/
Power Amplifier Selection
A prospective BUC must meet certain minimum requirements:
•
Minimum gain should be based on the required output power levels and cable losses. Most
modern BUCs seem to provide between 50 and 67 dB of gain, depending on power output.
The typical input power required for full power output varies between -20 and -30 dB.
•
Maximum phase noise levels need to be determined based on the data rates being used.
•
Frequency stability: Determined by externally applied 10 MHz reference oscillator. Typically
requires an approximate 1 part in 10
7
OCXO for C or Ku-Band operation. This represents a
possible 600 Hz error at 6 GHz or 1.4 kHz at 14 GHz transmit frequency.
•
Input Connector: 50 Ohm, Type N or TNC
•
Power Output: 1 to 20 Watts depending on satellite, location, antenna size, etc.
If the cable length between the modem and the BUC is very long then a higher voltage may be
desirable due to voltage drop in the cables.
3.2 LNB
Selection
It is doubtful that one could use a TVRO video class LNB and make it work in a data application.
This is mainly because these LNBs were designed with a very wideband video carrier in mind,
and the phase noise performance is far from that necessary for a lower data rate PSK carrier.
Today, data grade LNBs are still fairly inexpensive, but a prospective LNB must meet certain
minimum requirements:
•
Gain of approximately 45 to 70 dB
•
Maximum phase noise levels need to be determined based on the data rates being used.
•
Frequency stability: +/- 5 to +/- 25 kHz preferred, +/- 500 kHz acceptable if phase noise good.
