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WARNING: Disconnect and lockout AC primary power prior to servicing
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6.4.1.1 Logic Card Detailed Circuit Description (Drwg: 839-7900-043)
The set controls are adjusted to determine the point at which the level is considered too
low to be satisfactory. When the exciter RF level is below this point, the comparator
output switches to a high state and the green LED is extinguished. This logic state is
OR
’d with the unused aural and will control the output of that gate. The logic flow states
are annotated on the drawing. K1 is a magnetic latching relay and will retain its logic
state during a power failure. The K1 relay controls the status of the status LEDs and the
Q1 drive transistor for the 4 port coax transfer relay. The coax relay is energized when B
exciter is selected. Automatic or manual only switching is selectable by the switch on the
front of the module or by local or remote GUI control. This status is stored by another
magnetic latching relay K2. Automatic switching will occur if the active exciter RF level
is lower than the level determined by the SET adjustment. This level is usually 50%, but
is adjustable to other values if required.
The input labeled MUTED acts as a switching inhibit control line to prevent switching
when the control system is in mute or VSWR foldback. This will not inhibit the manual
switching mode.
6.4.1.2 Exciter Switcher Relay Board Panel (Drwg: 839-7900-080)
This board switches the I/O lines’ main controller to the I/O connector on the back of the
exciter to control the on air exciter. The I/O connection of the standby exciter is not
connected to anything. This board has jumpers to select analog or digital operation.
The RF detectors (815-5476-003) are not part of the relay board but are mounted
adjacent to the board. The detector blocks have internal diodes that detect the RF level.
The resulting DC voltage is cabled to the logic card comparator inputs.
6.4.1.3 Operational Setup and Adjustment
Following is a procedure for Operational Setup for the exciter switcher. This procedure
will set the threshold adjustments which determine when to switch exciters.
IMPORTANT:
This procedure should only be done AFTER any AGC adjustments are made.
If AGC adjustments are needed, perform them first, then do the switcher threshold
adjustment.