Functional Description; Architecture; Features; Digital Channel Filters - CommScope Node AM4 Manual

4. Functional Description

4. Functional Description

4.1. Architecture

The Node AM4 is designed to amplify signals between multiple mobiles and a base
station. The unit consists of a filter and amplifier chain in the downlink and one filter and
amplifier chain in the uplink. The uplink and downlink paths are connected via a duplexer
on both ends of each path. After that the signals are combined by the crossband coupler
with the other frequency bands.
In the uplink path, a signal originating from the mobile is divided by the crossband coupler
into the different frequency bands and is separated from the downlink signal via the UL
IN duplexer. It is then amplified by a low noise amplifier (LNA), which is like the duplexer
part of the RF card. The RF card down-converts the signals to the IF and converts the
analogue signal into a digital signal. Digital filtering / signal processing is done at the main
board of the subrack with single band RF cards, and with dual-band RF cards in the cards
themselves. Then, the digital signal is converted into an analogue signal, is up-converted
and amplified. Finally, the signal is sent to the PA and combined with the downlink signal.
After that the signals from all RF cards are combined at the crossband coupler and
forwarded to the Base Station port of the Node AM4 system.
In the downlink path, a signal originating from the base station is divided by the crossband
coupler into the different frequency bands and is separated from the uplink signal in the
donor duplexer. It is then amplified by a low noise amplifier (LNA), which is like the
duplexer part of the RF card. The RF card down-converts the signals to the IF and
converts the analogue signal into a digital signal. Digital filtering / signal processing is
done at the main board of the subrack with single band RF cards, and with dual-band RF
cards in the cards themselves. Then the digital signal is converted into an analogue
signal, is up-converted and amplified. Finally, the signal is sent to the PA and combined
with the uplink signal. After that the signals from all RF cards are combined at the
crossband coupler and forwarded to the mobile port of the Node AM4 system.
Apart from the difference in digital signal processing as explained in the sections above,
the functionality of dual band and single band RF cards is principally identical in both the
UL and DL paths.
For an overview of the individual components, please refer to chapter 4.3 Components.

4.2. Features

4.2.1. Digital Channel Filters

The Node AM has a multitude of digital filters. The maximum bandwidth of each filter is 5
MHz. If a greater bandwidth than 5 MHz is required, two or more sub-band filters are
linked together without increased amplitude or delay ripple. The number of sub-band
filters is automatically allocated and shown by the repeater software (Technician Setup
page).
The user has to select the downlink start and stop frequencies (wide-band filter load) or
centre frequency and filter bandwidth (narrow-band-filter loads) of each sub-band filter.
For further information regarding sub-band filter settings refer to the User's Manual for
the Node AM software.
Page 34 MF0121ACP_uc.docx Manual for Node AM4