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When troubleshooting RF issues, and when surveying challenging RF en-
vironments, it’s important to have a spectrum analyzer capable of measur-
ing the frequency that you are working with. An attenuator 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 fi ber/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 fi lter 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 fi lter, you can decrease the RBW, to see the close-in-frequency sig-
nals. 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 lat-
ter reduction prevents the composite power of the multiple signals from exceed-
ing an acceptable level. Add fi xed attenuators in line with the donor antenna
line/DAS feed to keep signals below the levels indicated above.
Summary of Contents for CSI-DSP95-252-L7
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