Digital Repeater Line
DSP85 Series
WESTELL.COM
© 2016 Westell Technologies
14 June 2016 Doc. No. 960-1666-MNL rJ
1.877.844.4274
Page 19 of 77
2
Optimizing the System during Installation
2.1
System Setup Considerations
Check all cables for shorts and opens. Verify that there are no cables with loose or poor connections. RF leakage
could cause oscillation to occur under some conditions.
Check the rooftop antenna (donor antenna), if directional, for proper alignment along the calculated compass
heading. Typically, the directional antenna is aimed at the same site that your handset uses, but it may not always
be. It is critical that the installer contact the service provider for information about, and approval of, the selected cell
site before the system is activated.
IMPORTANT
The installation height of the antenna for AWS band (1700/2100 MHz) operations is
limited to 10 meters above ground for compliance with Section 27.50.
If cables and alignment are acceptable and a problem persists, it may be necessary to use a spectrum analyzer to
examine the signal environment in which the repeater is operating. The existence of strong adjacent channel signals
within the frequency band(s) can cause the AGC to reduce the amplifier’s gain or cause alarms. In some cases,
additional filtering or attenuation may be required to reject these unwanted signals. In some instances, the donor
antenna can be repositioned horizontally, to place the interference source in an antenna pattern null. There also may
be some cases where the interference from outside signals is so great that they cannot be filtered, reduced or
eliminated without expensive (and possibly prohibitive) measures. In these cases, it may not be practical to use the
repeater for providing coverage to these sites.
2.2
Suggested Spectrum Analyzer Setting
When troubleshooting RF issues and surveying challenging RF environments, it is important to have a spectrum
analyzer that is capable of measuring the frequency you are using. Use an attenuator to protect the input when
connected to a source of RF power, such as a repeater or a powered DAS.
Measure both uplink and downlink.
Measure downlink on the donor cable and at the output (server) port of the powered repeater.
Measure uplink at the lead from the DAS (on fiber-powered DAS, where the lead would connect to the server port on
the repeater) and at the donor port with the repeater power on.
Measurements may also be necessary at server antenna locations. The spectrum analyzer must be equipped with a
whip antenna.
Set the resolution bandwidth (RBW) to 200 kHz for GSM and 1 MHz for CDMA. If you cannot select these values, use
the closest available values. Set the video filter to about one-tenth of RBW. Set other settings, such as span, to the
appropriate values. Ensure that there are no signals above the top of the screen.
If you cannot see an adjacent out-of-band signal when using the 1 MHz RBW filter, decrease the RBW to see the
close-in-frequency signals. Set the RBW back when you want to measure the power level.