Westell Inc. CSI-DSP85-U7C User Manual
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When troubleshooting RF issues, and when surveying challenging
RF environments, it’s important to have a spectrum analyzer capable
of measuring the frequency that you are working with. An attenua-
tor should be used to protect the input, when connected to a source
of RF power such as the repeater or a powered DAS.
Both Uplink and Downlink should be measured. Downlink should be
measured on the donor cable and at the output (server) port of the
powered up repeater, and Uplink at the lead from the DAS (on fiber/
powered DAS’s, where the lead would connect to the server port on
the repeater) and at the donor port with the repeater powered up.
Measurements may also be necessary at server antenna locations.
Your spectrum analyzer will need to be equipped with a whip
antenna for this.
Resolution Bandwidth (RBW) should be set at 200 kHz for GSM and 1
MHz for CDMA. If you cannot select these values, the closest
available values should be used. Video filter should be about one
tenth of RBW. Other settings like span are whatever is appropriate.
One should also make sure 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, you can decrease the RBW, to see the close-in-
frequency signals. Be sure to set the RBW back when you want to
measure the power level.
Suggested spectrum analyzer setting:
RF Notes:
To prevent overload of the DSP input stages, the maximum measured
level of in-band or out of band signals should be less than -50 dBm when
the DSP gain is set to 85 dB, -40 dBm when set to 75 dB, etc. This applies
when there is one dominant signal and applies TO BOTH THE DOWNLINK
AND UPLINK. If there are two dominant signals, and the gain is set to 85
dB, then the level of each signal should be kept to less than -53 dBm.
With three signals, each should be less than -55 dBm. With ten signals
each should be less than -60 dBm. This latter reduction prevents the
composite power of the multiple signals from exceeding an acceptable
level. Add fixed attenuators in line with the donor antenna line/DAS feed
to keep signals below the levels indicated above.