User's Guide

Maintenance Handbook (1)
Baltimore Radio Repeater System
Handbook No. 60-166101HBKM Page 7 of 33
3. EQUIPMENT OVERVIEW/SPECIFICATIONS
The Baltimore repeater system consists of several items of hardware:-
Master Site Preston UHF Air Interface Channelised Amplifier (60-166101, rack mounting)
Master Site OCC UHF Air Interface Channelised Amplifier (60-166201, rack mounting)
Preston Six-Way Fibre Optic Master Site (60-166301, rack mounting)
OCC Six-Way Fibre Optic Master Site (60-166401, rack mounting)
Remote Site High Power UHF Bi-Directional Amplifier (60-166501, wall mounting)
MOCE Site Air Interface Repeater (60-166801, wall mounting)
6 x 114Ah Battery Backups (80-333201, wall mounting)
There are two master sites, one at PRESTON and one at OCC, each has a 19” rack cabinet
containing the four off-air receiving shelves, which also contain the power supplies and the DC/DC
converters (12V) for the FO shelf.
The master site equipment receives off-air transmissions which it channelises, (15 channels) and
sends this downlink signal data to six fibre optic RX modules. Remotely sited cell enhancers receive
this FO data, demodulate and amplify it and feed it to local LCX antennas.
At the remote sites, the same leaky feeder antennas receive mobile signals, band selectively amplify
them and send this uplink data back by FO to the master site where it is demodulated, channelised
and broadcast on the same air interface antenna that received the downlink signal.
Existing in the current system are bi-directional amplifiers in the 800MHz bands. These signals are
catered for using specialist cross-band couplers so that the 800MHz signals bypass the 490MHz
system path with negligible loss.
20dB couplers fitted at various points in the system ‘tap-off’ a signal suitable for monitoring the RF
power in any path.
Each active device is alarm monitored and these alarms are available either as separate volt-free
relay contact pairs, in groups (e.g. all downlink power amplifiers), or as an alarm summary of the
whole system with locally visible indications (LEDs).
Six 114Ah battery backup systems ensure no loss of coverage should mains power fail. At the time of
writing this document no information was available on which items of the system were to be fitted to
the battery backups.