Netro RU28G-00 SRU Manual
SRU Installation
1. SRU Antenna Alignment
1.1 Introduction
This chapter gives instructions for aligning the SRU antennas to the BRU for maximum
signal strength.
Before alignment of the antenna, perform the following steps:
1. Refer to “SAS Installation Manual” and perform the indicated procedures. Most of the
principles used to locate a site for the Base Radio Unit can be applied to SRU
placement.
2. Install the Base Station as explained in “BSIS Installation Manual.”
3. Install one or more Subscriber terminals as explained in “SAS Installation Manual.”
4. Install the Link Explorer PMP and configure the Base Station as explained in “BSIS
Installation Manual.”
The direction in which the SRU antenna points must be aligned to the location of the
associated BRU to ensure that maximum received signal strength is achieved at both ends of
the microwave link. Although the antenna radiation pattern is typically thought of as a
“beam,” the radiation pattern actually consists of “lobes,” as shown in Figure 1-1. How you
planned your network will help identify which specific antenna is used in this ST and the
BRU for the link.
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SRU Installation
Figure 1-1Antenna Pattern
1.2 SRU Al ignment
This chapter contains information about SRU alignment.
1.2.1
1.2.1 Preparation and Overview of Procedure
1.2.11.2.1
It is recommended that a person be present at both the SRU and the associated BRU for
this antenna alignment procedure. It is also advisable to have some form of communication
between the two sites, such as cell phones, two-way radios or telephones. Mirrors or strobe
lights (for flashing the path) are recommended for situations in which the antenna locations
are not readily visible from one another, as a result of distance or atmospheric conditions. It
is absolutely essential that there are no obstructions present in the path of the beam.
The objective of this procedure is to aim the main lobe of the SRU antenna precisely in the
direction of the associated BRU. This is accomplished by performing a rough visual
alignment first; then further alignment is performed while monitoring the Receive Signal
Level at the Subscriber Radio Unit with a voltmeter. The alignment process consists of
adjusting the direction of the SRU until the received signal level is maximized.
Do not confuse the alignment directions (horizontal, vertical - that is, azimuth, elevation)
with the polarization of the antenna feed assembly. Antenna polarization should be
established prior to installation. Verify that the polarization of the SRU matches the
polarization of the BRU.
Preparation and Overview of Procedure
Preparation and Overview of ProcedurePreparation and Overview of Procedure
Connect a Voltmeter to ensure that the SRU is getting power. A reading of zero means that
there is a problem with the SRU, SAS, or cable (or voltmeter). A reading of +4.0 Volts
indicates it is likely that the SAS is not admitting and is presently scanning through the
channels of the channel plan as it attempts to admit. Or that the SAS cannot admit because
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SRU Installation
the SRU is drastically out of alignment. Re-align the SRU visually and wait for it to readmit. If the reading is between 0 Volts and 4 Volts, then the SAS has admitted.
Tighten the lock nut/washers to eliminate most freeplay, but not so tight that you can’t
move the SRU in both directions.
During the rough alignment procedure (see below) the purpose is to align the SRU visually,
both elevation and azimuth. If it is totally off-lobes it will read very high (and you’ll be able
to see that it is not aligned). Attach the voltmeter. Adjust it visually in both dimensions to
determine where the main lobe is centered.
Adjust the azimuth for the maximum reading. Tighten the azimuth bolts bit by bit without
losing the reading. Repeat for elevation. Remove the voltmeter and replace the hanging cap.
The purpose of the fine alignment procedure (see below) is to achieve precise antenna
alignment, which is critical for optimum system performance. Make sure the antenna is
aligned on the main lobe as shown in Figure 1-2, this arrangement produces a significantly
lower receive signal strength, making your system more vulnerable to outage due to fading.
Parabolic antennas are highly directional (focused) and any movement of the antenna during
alignment should be performed SLOWLY. This allows observation of the side and main
lobes during antenna movement. It is important to verify that the SRU antenna is aligned to
the MAIN LOBE.
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Figure 1-2 Correct Anten na Alignment
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