User's Guide

Maintenance Handbook (1)
Baltimore Radio Repeater System
Handbook No. 60-166101HBKM Page 22 of 33
4. INSTALLATION & COMMISIONING
4.1 Initial Installation Record
When this equipment is initially commissioned, please use the equipment set-up record sheet in the
Appendices. This will help both the installation personnel and AFL should these figures be needed for
future reference or diagnosis.
4.2 Antenna Installation & Gain Calculations
1 Most Cell Enhancers require two antennas, one a highly directional Yagi or similar directed
towards the donor cell base station, and one a leaky feeder, omni-directional antenna or Yagi to cover
the area in which the mobiles are to be served.
2 The maximum gain at which the Cell Enhancer can be set is limited by the isolation that can
be achieved between these two antennas. Therefore when the antennas have been installed, inject a
signal (at a known power level) into one of them and measure the signal level received by the other
antenna on a spectrum analyser. The isolation can then be calculated as the difference between
these two figures. The gain in each path of the Cell Enhancer should be set at least 10 dB below this
figure, using the switched attenuators as described below in paragraph 5.
3 Now measure the received signal from the donor cell at the input to the Cell Enhancer (base
port). The gain of the Cell Enhancer downlink path should be set such that the donor site signal will
not overload the Cell Enhancer amplifiers. It is recommended that the input level should be less than -
50dBm at the input of the Cell Enhancer (Base port). (This figure is assuming maximum gain, and
may be increased by the value of the attenuator fitted in the downlink path.)
4 Ensure that the mobile facing antenna has at least 70 dB isolation from the nearest mobile.
(This is normally easily achievable when using a leaky feeder antenna, but usually requires positional
adjustment when using a Yagi.)
5 The Cell Enhancer gain is fixed by setting the attenuation in each path (uplink and downlink)
between the first two amplifier stages (see markings within the Cell Enhancer or layout drawings for
the exact attenuator locations). Note that the uplink (mobile to base) and downlink (base to mobile)
path gains are set independently. This allows the paths to have different gains if required to set the
correct output power levels. The attenuation added into the path is a direct reflection of the active
switch positions, i.e. switch 2 (2dB) and switch 4 (8dB) would add 10dB into the path.
6 It is recommended that the gains are set such that the Downlink channel output levels from the
Cell Enhancer are typically +20dBm.
(Input level + Gain = Output level).