Product Drawings Chapter 3

AE02B-A3659 Rev -- FUNCTIONAL DESCRIPTION
Document use is restricted to that described on cover 3-3
Figure 3-2. SelectAmp NBPCS-900-3 Outline Drawing, rear view.
3.2.3.1 DOWNCONVERTER
The downconverter board consists of a mixer driven by a synthesizer, a crystal filter centered at 45 MHz
with 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 stage
to provide overall gain adjustment. A Receive Signal Strength Indicator (RSSI) circuit measures the
received signal strength and outputs a dc voltage to the Control/Distribution board. The DC current draw
of each gain stage is monitored by a window comparator. The window comparator indicates a fault, if the
gain stage has an open or short condition. The output of the down converter is fed to the upconverter
board.