Copyright 2005 ISC Technologies
4.2.5 Timer and Fan Driver
The oscillator and programmable timer (U10), has its oscillation frequency determined by
R46, R47, and C48 (fosc = 1/(2.3 R47 C48) when R46 = 2*R47). This driver operates as a
one shot 2 minute timer, and its counter is reset when it is powered up or pin 6 of U10 is
set. The counter will count up to 2 minutes of logic low at pin 6 of U10, then reset the Q
output to a logic low.
There are four possible inputs that reset the 2 minute timer; power on, high RF input level,
high RF output level, and overheat sensor.
Note
The fan may be jumpered on by installing JR25.
4.2.6 Overheat Sensor and Reference Temperature Level
If the ambient temperature detected by the temperature sensor is higher than the reference
temperature (set by R14, and R28, or R51), the temperature sensor turns on switch Q2.
Switch Q2 then turns on overheat LED D10, and sets the alarm. The temperature sensor
has hysteresis determined by R29 and R32.
5 INSTALLATION
5.1 Overview
The transmitter location should be chosen to protect the equipment from dust and extreme
environmental conditions. The transmitter can either be installed in any standard EIA 19-
inch rack or ordered with one of two optional 19-inch rack cabinets. An optional cabinet can
be ordered for indoor transmitter locations. Before installing the cabinet, open the
transmitter’s cabinet door and examine all equipment closely to ensure that all packing was
removed and that all required printed circuit boards, other plug-in units, bolt-on equipment
and electrical connections are secure. Replace any panels removed, and close the cabinet
door after your inspection.
Cabinet Installation
DANGER
The optional cabinet, with one transmitter, has an approximate mass (weight) of 76
kg (167 lbs.). Ensure that the proper equipment and the required number of persons
are available when lifting or moving your cabinet-installed transmitter to prevent
injury to personnel or equipment.