User's Manual

APEX™ Exciter Incorporating FLO™ Technology
Details of the System Setup Screens Navigating the LCD Display Screens
2604s300.fm
03/08/07 888-2604-001 Page: 3-43
WARNING: Disconnect primary power prior to servicing.
3.6.5.1 VSWR Foldback Parameters
The exciter VSWR foldback function is not used in the Atlas series of transmitters, but the
circuit is still in place and it will reduce the exciter output power if the three programable
VSWR parameters on this screen are improperly set up. Normal VSWR parameter setup
for the Atlas series transmitters are given below.
The External I/O Setup screen is shown in Figure 3-36. This screen includes a VSWR
foldback function which has three programmable parameters which are listed below.
• VSWR F/B Low Threshold. The setting for Atlas transmitters is 0.25 Vdc. This repre-
sents the input voltage level where the reduction of exciter output power starts.
• VSWR F/B High Threshold. The Atlas transmitter setting is 5.0 Vdc. This represents
the input voltage level which causes the maximum exciter output power reduction.
The VSWR F/B input voltage causes a linear reduction of exciter output power from
the normal exciter output power level (VSWR F/B input voltage below the low
threshold) down to the preset maximum allowable exciter output power reduction
(when the VSWR F/B input voltage reaches the high threshold).
• VSWR Max F/B Level. The default value is 70%. This is the maximum allowable ex-
citer output power reduction, listed as a percent of the normal exciter output power,
when the VSWR foldback input voltage to the exciter reaches the VSWR F/B High
Threshold.
When VSWR foldback is active the following indications will be present.
• The system control light on the front panel will be lighted yellow.
• The foldback readout on the External I/O status screen will be yellow, see Figure
3-25, on page 3-27.
3.6.5.2 RF Present Cutoff
Another programmable function listed in the External I/O Setup screen, shown in Figure
3-36, is the RF Present Cutoff. When the exciter average output power drops to this level,
the RF Present (output) signal from the exciter changes from low (exciter is ok) to high
(exciter has failed due to low output power). This signal is sent to the transmitter control
logic and causes it to switch to the other exciter. The RF present cutoff parameter is
programmable from 0 to 250 mW average exciter output power, with a typical setting of
half of the normal exciter output power.