LIBRA 631 User manual
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Test Center
Instruction Manual
General Notation
On Grounded Grid amplifiers, we do not recommend checking modulation
at higher powers. Grounded Grid amplifiers will not be able to output 100%
modulation in the A.M. mode, however, the feed through powerprevents
the grounded grid from being fully modulated. This is the reason A.M.
modulation should be checked at the transmitter, or with theLinear
Amplifier in standby position. Libra 631
123
45678
Installation Instructions
One of the unique features of the Libra 631 is the
ability of the unit to monitor all functions of the
transmitter simultaneously.
The test center can be installed at any point in
your transmitter line.
Starting Tips
Operating Instructions
Watts
SWR Set
A.M. Modulation Check
1. Set SWR and MOD RF level controls to minimum.
2. Set Range Switch to 1000.
3. Set SWR and MOD functions on each Range to
prevent damage to the meter movements.
The Libra 631 Test Center will indicate the power output (in
watts) of your equipment at the point in the transmission line
where you have installed the test center. To measure any
power from 1 to 1000 watts, just set the RF Power Range
Switch (#6 FIG. 1) to the appropriate range: 10, 100, 1000
watts. Key the transmitter and read the wattage on the
corresponding scale of the RF Power Meter (#2 Fig. 1).
NOTE: If power output is uncertain, use the highest range
and work down until the range is appropriate to prevent
possible damage to the meter movement.
1. Operate SWR Set Control Switch (#4 Fig. 1) to Set Position.
2. Turn SWR RF Level Control (#5 Fig. 1) to Min.
3. Key transmitter and turn SWR RF Level Control clockwise
(#5 Fig. 1) to give a full scale meter reading to Set Line on
the SWR Meter (#1 Fig. 1).
NOTE: The SWR Functions need to be performed on each
wattage range to prevent possible damage to the meter
movements.
1. Operate MOD SET Control Switch (#8 Fig. 1) to SET position.
2. Turn MOD RF Level Control (#7 Fig. 1) to Min.
3. Key transmitter and turn MOD RF Level Control (#7 Fig 1)
clockwise to give a full scale meter reading to Set on the
Modulation Meter (#3 Fig. 1)
4. Operate MOD SET Control Switch (#8 Fig. 1) to MOD
position. Key transmitter and talk or steadily whistle into the
microphone. Read Modulation percentage directly on the
modulation meter (#3 Fig. 1)
NOTE: A.M. modulation check functions must be performed
on each wattage range, to prevent possible damage to the
meter movements.
Transmitter LIBRA Test Center
RG/58BU
Input Antenna
1. SWR Meter
2. RF Power Watt Meter
3. Modulation Meter
4. SWR Set Control Switch
5. SWR RF Level Control
6. RF Range Switch
7. MOD RF level Control
8. MOD Set Control Switch
Figure 1
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