FS71C-85 Series User Manual
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Copyright © 2015 Fiber-Span
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Detailed Description
This section deals with the actual components that are
assembled to make up the DHRU. The main subassem-
blies/subsystems are:
1. RF Amplifi ers - These provide RF signal amplifi ca-
tion.
2. Duplexers - These units separate and combine
downlink and uplink frequency spectra, and re-
duce interference.
3. Digital Signal Processor - Provides settable nar-
rowband fi lters around eacch incoming channel.
4. Control Board - Provides the USB interface for GUI
Program for setting channel centers, fi lter band-
Overview
Ampli ers
There are two types of amplifi ers that Fiber-Span uses
to provide the appropriate amount of gain required to
provide coverage solutions:
1. LNA – The LNA (low noise amplifi er) amplifi es
the uplink RF signals after they pass through the
duplexer. A low noise amplifi er with 40dB of gain
provides a low noise fi gure.
2. Power Amp – The output power amplifi er pro-
vides the downlink gain and has some additional
features like ALC (automatic level control) and
pre-distortion.
The amplifi ers that Fiber-Span utilizes are powered
from a DC power supply. The RF amplifi ers are type
AB broadband. Their current varies with their RF power
load.
The power amplifi ers employ an Automatic Level Con-
trol (ALC) circuit to ensure the RF output power does
not destroy the fi nal gain stage of the RF amplifi er.
The input signal to the power amplifi er can be reduced
to prevent the ALC circuit from becoming active. This is
done by adjusting the
Attenuator
control available on
the GUI Interface.
The amplifi ers also employ a form of pre-distortion
to allow multiple channels to operate at higher levels
with reduced intermodulation signal levels.
The input RF signal into the amplifi er is pre-distorted
such that after amplifi cation, the intermodulation prod-
ucts are reduced from what would normally be experi-
enced in an amplifi er without pre-distortion.
When Power Amplifi er (PA) input exceeds ALC range,
the power amplifi er latches in MUTE mode, meaning
the PA is OFF, to protect itself from destructive damage.
This state requires technical intervention in order to
return the PA to the UNMUTED state:
1.
Correct the cause of high level input. This can
be done by performing the following: a. Discover and
mitigate any input signal(s) causing the over-driven
state b. Reduce gain to an appropriate level
2.
Using the GUI, MUTE the PA
3.
Using the GUI, UNMUTE the PA
widths etc. and getting alarms in the DHRU. Also
provides a single contact closure summary alarm
via the circular connector.
5. Power Supply - This unit converts AC Primary
Power to DC Power as required by the active
components.
6. GUI-based Monitor & Control Interface - This
subsystem offers signifi cant user benefi ts and
capabilities.
This utility allows the user to optimize the equip-
ment confi guration settings and monitor Alarm
Status.
