HR
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ANDBOOK
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2.5.3
LNA/LNB voltage boost - plug-in modules
The output voltage of any module equipped with an internal 13/18/22 volt power supply (op
tion “5”
and “L”) can have its output voltage increased to allow for cable losses, the output voltage is
increased by +1V nominally. This is implemented using the modules software configuration. This
option is NOT available on units equipped with +5V, +12V or external voltage feeds.
2.5.4
LNA feed - Purple link modules
Modules in this range offer an internally gen5V or +12V feed and external feed only.
2.5.5
LNA feed
– Voltage versus current characteristic
The LNA voltage is fed via a wideband choke (providing RF isolation) a low value resistor (used for
current monitoring) and a resettable fuse (providing protection). These elements add a series
impedance of approximately one ohm. The graph below shows how the voltage current characteristic
of a typical module with 12 volts fed to into the LNA feed via an external feed from the module
connector “LNA feed” pin.
When using LNA/LNB feeds care must be taken to allow for voltage drops through the input feed
network as well as voltage drops in the output feed network. For example RG58 may have a
resistance of up to 0.2 ohms per meter; this varies greatly between different types and constructions
of cable.
Voltage measured at RF connector versus load current, input voltage 12V
NOTE: the graph shows the module operating beyond its specification limit to illustrate the margin of
safe operation, it should not be operated beyond its specification limit.
2.5.6
BUC feed - receiver modules
Receiver modules may optionally provide block up converter (BUC) power feeds. These provide a
DC path to the receiver RF output to provide power to a BUC or other connected module. The
external DC paths (option 3) of a module may be accessed via the chassis connector for Plug-in
modules (see your chassis handbook).
0
No LNA feed
1
Internally gen5 ± 0.5V at 80mA
2
Internally gen12 ± 1V at 300mA
11.3
11.4
11.5
11.6
11.7
11.8
11.9
12
12.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
V
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lt
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a
t R
F
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(V
)
Load Current (A)
LNA feed
– Voltage versus current
