User's Manual

Bronx Justice Centre Radio Repeaters
Handbook Number: 80-283501HBKM Page: 10 of 86
4. SYSTEM DETAILS
4.1 VHF Channel Selective Cell Enhancer Rack (50-146501)
4.1.1 VHF Cell Enhancer Rack Description
The VHF cell enhancer, built into ten 19” wide shelves and housed in a 43U high equipment rack, is a
mixture of simplex (Tx & Rx on one frequency) and duplex (Tx & Rx on two separate frequencies)
systems, three simplex and two duplex. There are separate Rx and Tx antennæ for the VHF and UHF
bands and a composite antenna for the 800MHz bi-directional system. All VHF input channels, up and
downlink are selected by narrow band crystal filters, and all outputs have ferrite isolators fitted in
series to increase the isolation between adjacent channels and protect the transistors of the power
stages from possibly damaging reflections. Each active module has a volt-free relay contact pair
alarm which is looped to provide a normally-closed system. The inputs and outputs are handled by
combining and splitting shelves and the channel processing and amplification is all within the BDA
channel shelves.
The simplex Tx/Rx system relies upon noise-free paths to enable accurate detection and muting to
occur and for this reason it is not recommended to disturb these circuits as they are carefully set up
by AFL when system tested and should not be adjusted except by expert personnel.
A dedicated power supply shelf provides the DC needed by the VHF system, (a similar power supply
is used in the UHF system also), and all alarms are volt-free relay contact pairs, looped in each shelf
to provide a summary alarm with local failure indicator, suitable for integration into any such existing
system. No battery backup is provided for this system and so should the mains supply fail, this system
could not function.
4.1.2 VHF Cell Enhancer Rack Electrical Specification
PARAMETER SPECIFICATION
153.965MHz* (Ch. 1)
154.755MHz
154.785MHz
154.980MHz
158.925MHz* (Ch. 2)
VHF downlink
151.355MHz* (Ch. 1)
154.6575MHz* (Ch. 2)
154.755MHz
154.785MHz
VHF Frequencies:
154.980MHz
VHF uplink
Bandwidth: 15kHz (up & downlink)
Downlink Gain(Duplexed): 97 dB min
Downlink Gain(Simplex): 97 dB min
Uplink Gain (Duplex & Simplex): 100 dB min
Gain Adjustment: 0 – 15dB (in 1dB step)
Uplink Power: >2-5Watts
Downlink Power: >10Watts
AGC: Fitted in all channel selective modules
Noise Figure: <6dB (@ maximum gain)
VSWR: better than 1.5:1
Impedance: 50ȍ
RF Connectors: N type, female
Supply voltage: 110V AC (nominal) @ 43-63Hz
System power requirement: 24V DC @ <13A
1 Amplifiers Alarms Fitted:
(volt-free contacts/TTL)
2 PSU
* = duplex channel