User's Manual

2. Preliminary Decisions
AMPS EAC-2100 Manual: (Draft, 02/01) Page 2-12
2.4.3 Measuring Signal Level and Isolation (Continued)
Signals from the cellular system will likely be stronger than the sweep signal received from the
tracking generator, and difficulty may be experienced in measuring the actual isolation.
Many spectrum analyzers have difficulty reading signals below -60 to -70 dBm when sweeping
a broad bandwidth. In this case, the band may be swept in smaller frequency segments, or a
separate signal generator with higher possible output power may be substituted for the tracking
generator. The signal generator frequency and amplitude can be manually changed to avoid
conflict with existing strong signals from the donor and other cell sites.
The signal generator should be manually swept through both the low split and the high split
bands to determine the minimum isolation point.
To measure isolation:
1. Supply a known signal level of about 0 to +20 dBm across the band into one of the antenna
feeds (M1, D1, or mobile).
2. Using test equipment, measure the signal level received on the other antenna feeds.
3. Adjust antenna locations and orientations to achieve the desired antenna isolations.
4. Move the signal source to other antennas, and recheck the isolation. Be sure to check both
the forward and the reverse bands.
5. If the D1 antenna has been repositioned, recheck the received donor DCCH channel signal
level to verify that it exceeds -75 dBm.
6. Record these measurements.
Refer to Appendix B for a more detailed procedure for measuring isolation.