Andrew NBPCS-9002W Channelized Paging Repeater User Manual Exh D Chapter 3

Andrew Corporation Channelized Paging Repeater Exh D Chapter 3

Exh D Chapter 3

AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTIONDocument use is restricted to that described on cover 3-1CHAPTER 3FUNCTIONAL DESCRIPTION3.1 OVERVIEWThe SelectAmp Channelized Paging Repeater accepts inputs in the 928 – 942 paging band, and selectivelypasses one discrete channel in each band while rejecting the others. In the forward channels this isaccomplished by downconverting the desired signals to a 45 MHz intermediate frequency and usingnarrowband crystal filters to provide adjacent channel rejection. The reverse path is not channelized,passing all frequencies in the 897 – 903 MHz band.3.2 FUNCTIONAL DESCRIPTIONRefer to Figure 3-1. The amplifier contains two paths; forward for the base station to pager signal andreverse for the pager to base station signal. The forward path includes a diplexer, low noise amplifier andsplitter, channelizer, combiner, and power amplifier. The channelizers determine the frequencies to beamplified and provide the gain control. The reverse path includes a diplexer, broadband module (amplifierand filters), and a power amplifier. Diplexing of the forward and reverse channels is accomplished bydiplexer filters tuned to the appropriate frequencies.3.2.1 DIPLEXERThe diplexer module consists of dual filters with a common port on one end and two separate ports on theother. One side of the diplexer is tuned for the forward channel, the other side for the reverse channel. Insertion loss of each filter is 2 dB maximum and 65 dB minimum rejection to the opposite band.3.2.2 BROADBAND MODULEThe broadband module contains three boards, each mounted in its own compartment. The forward channelsignals are routed through the LNA/Splitter and Combiner boards. The reverse channel signal is routedthrough the 901 MHz board. Each board is described in more detail below.3.2.2.1 LNA/SPLITTERThe LNA/Splitter module contains the first active devices in the forward channel path. It consists of a lownoise amplifier, 3-way power splitter, and a gain stage and filter per path. The amplifiers bias voltages aremonitored for a fault condition and reported to the control/distribution module.3.2.2.2 COMBINERThe Combiner module consists of a 3-way power combiner, a gain stage and filter, and a level detectorcircuit.
AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTIONDocument use is restricted to that described on cover 3-2Figure 3-1. SelectAmp NBPCS-900-3 Outline Drawing, front view.3.2.2.3 901 MHZ REVERSE CHANNELThe 901 MHz reverse channel module provides four gain stages, filtering, and gain adjustment via the frontpanel.3.2.3 CHANNELIZERThe channelizer module contains three boards, each mounted in their own compartment. These threeboards, which are described below, provide the channel selectivity. The channelizer module gain isapproximately 40 dB.CHANNELIZERS (A4,A5,A6)DIPLEXER (A8)FRONT PANEL (A13)BROADBAND (A7)FWD CHANNEL PA (A12)REV CHANNEL PA (A10)CONTROL/DISTRIBUTION (A1)DIPLEXER (A9)POWER SUPPLY (A2)
AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTIONDocument use is restricted to that described on cover 3-3Figure 3-2. SelectAmp NBPCS-900-3 Outline Drawing, rear view.3.2.3.1 DOWNCONVERTERThe downconverter board consists of a mixer driven by a synthesizer, a crystal filter centered at 45 MHzwith either a 12.5 KHz (930 MHz channelizer), a 50 KHz (940 MHz ReFlex50 channelizer), or a 25 KHz(940 MHz ReFlex25 channelizer) 1 dB bandwidth. It has one fixed gain stage, and a variable gain stageto provide overall gain adjustment. A Receive Signal Strength Indicator (RSSI) circuit measures thereceived signal strength and outputs a dc voltage to the Control/Distribution board. The DC current drawof each gain stage is monitored by a window comparator. The window comparator indicates a fault, if thegain stage has an open or short condition. The output of the down converter is fed to the upconverterboard.
AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTIONDocument use is restricted to that described on cover 3-43.2.3.2 UPCONVERTERThe upconverter board mixes the filtered 45 MHz IF with a signal from the synthesizer and outputs thesame frequency that was input to the downconverter. The upconverter consists of a mixer, gain stage, andfilter. The DC current draw of each gain stage is monitored by a window comparator. The windowcomparator indicates a fault, if the gain stage has an open or short condition.3.2.3.3 SYNTHESIZERThe synthesizer board consists of a synthesizer circuit that is driven by a reference oscillator and distributionamplifiers. The synthesizer operating frequency is programmed from the Control/Distribution module. Theforward channel frequencies are set with a computer that has Andrew designed frequency control softwareinstalled on it. This software is a Microsoft Windows 95/98/NT application that allows the operator to inputthe desired channel frequency. The Control/Distribution module converts the operator's input to theappropriate frequency command for the synthesizer. The output of the synthesizer is divided into adownconverter path and an upconverter path.3.2.4 POWER SUPPLYThe power supply assembly consists of a Power Entry Module and switching power supply. The powersupply accepts a 100 to 240 VAC, 3A, 50/60 Hz input and outputs +15 VDC for use by the rest of the amplifier. Power is distributed to the active modules through the Control/Distribution board.3.2.5 CONTROL/DISTRIBUTION MODULEThe control/distribution module distributes power to the other modules, receives and processes status andfault information, and provides forward channel frequency control. Power distribution consists of currentmonitoring of both the forward and reverse channel PA’s, linearly regulating the +15 VDC down to +12 and+5 VDC for various modules. Status functions include monitoring RSSI voltages from the channelizers,monitoring forward output power, and driving the appropriate front panel LED’s. Channel frequencyselection information is received via RS-232 from the front panel and is processed by an on boardmicrocontroller. This information is also stored in ROM (Read Only Memory), so that frequency settingsare not lost if AC input power is lost. The microcontroller sends the frequency information via a three wireinterface to the appropriate channelizer. Various faults on the channelizers, broadband, and thecontrol/distribution module itself are monitored and displayed on the front panel. A rear panel contactclosure (closed when unit is operating normally) is provided for external monitoring.3.2.6 POWER AMPLIFIER MODULESThe power amplifier module provides the final gain and power stages for the amplifier. A 5 Watt Peak ClassA linear amplifier is used for the forward channel. This 5 Watt unit has approximately 27 dB gain. A 1.6Watt Peak Class A linear amplifier is used for the reverse channel. The 1.6 Watt unit has approximately30 dB gain. The DC current draw of each power amplifer is monitored by a window comparator.
AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTIONDocument use is restricted to that described on cover 3-53.3 PROGRAMMINGThe amplifier forward channels are set by connecting a laptop computer with the supplied cable to the frontpanel connector.Details on setting the channels and software operation are provided in Appendix B.

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