LIBRA 712 User manual

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Libra 712/714
Test Center
Instruction Manual
712P and 714P Units ONLY
The 712P and the 714P units are equipped with a power
lead for the meter lights. In order to power the lights, the
red wire must be hooked up to +12 volts. The black wire
must be hooked to a ground. The switch located on the rear
of the unit will turn the lights on and off once power has been
hooked up.
LIBRA Test Center
Red wire - +12 volts Black wire - ground
Light Switch

Installation Instructions
The test center can be installed at any point in
your transmitter line.
Transmitter LIBRA Test Center
RG/58BU
Input Antenna
Operating Instructions
Watts
The Libra 712/714 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 2000 watts (4000 watts on 714), just set
the Mode Selector Switch (#1 FIG. 1) to the power setting. Set
the power range selector switch (#2 Fig. 1) to the appropriate
range - 20, 200, 2000 (or 4000 on 714) watts. Key the
transmitter and read the wattage on the corresponding scale.
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.
SWR Set
A.M. Modulation Check
1. Turn Mode Selector switch (#1 Fig. 1) to the FWD SET position
2. Turn RF Level Control (#3 Fig. 1) to MIN
3. Key Transmitter and turn RF Level Control (#3 Fig. 1) to give
a full scale meter reading to SWR SET on meter scale.
4. With Transmitter keyed, switch Mode Selector Switch
(#1 Fig.1) to REF position and read SWR ratio directly on
SWR Scale.
NOTE: The SWR Functions need to be performed on each wattage range
to prevent possible damage to the meter movements.
1. Turn Mode Selector Switch (#1 Fig. 1) to MOD SET position
2. Turn MOD RF Level Control (#4 Fig. 1) to MIN
3. Key Transmitter and turn MOD RF Level Control (#4 Fig. 1)
to read full scale to MOD SET on meter scale
4. With transmitter keyed, switch Mode Selector Switch
(#1 Fig. 1) to MOD position and talk or steadily whistle into
microphone. Read modulation percentage on AM MOD
scale
5. DO NOT CHECK MODULATION WITH HIGH POWER
NOTE: A.M. modulation check functions must be performed on each
wattage range, to prevent possible damage to the meter movements.
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.
714 Meter Scale Reading
Up to 20 Watts....................................................................................... 20 Scale
Up to 200 Watts ............................................................................ 20 Scale X 10
Up to 2000 Watts ........................................................................ 20 Scale X 100
Up to 4000 Watts .............................................................................. 4000 Scale
712 Meter Scale Reading
Up to 20 Watts....................................................................................... 20 Scale
Up to 200 Watts ............................................................................ 20 Scale X 10
Up to 2000 Watts ........................................................................ 20 Scale X 100
1. Mode
Selector
2. Power
Range
Selector
3. SWR RF
Level Control
4. MOD RF
Level Control
Figure 1