MFJ-976 Legal Limit Fully Balanced Antenna Tuner
Instruction Manual
4
Installation
1. Place the tuner in a convenient location at the operating position. The terminals on the rear of the tuner will
have high RF voltages present during operation. These voltages can cause serious RF burns if the terminals
are touched while transmitting.
Be sure to locate the tuner so these terminals cannot accidentally be
contacted during operation.
2. Install the tuner between the transmitter and the antenna. Use a 50-ohm coaxial cable (such as RG-8/U) to
connect the transmitter to the connector marked
TRANSMITTER
on the rear of the tuner (see Figure 2).
3. Connect the antenna feedline to the tuner as follows:
NOTE: The MFJ-976 can be used to tune antennas fed with a balanced or unbalanced
feedline. Two jumpers are installed at the factory for unbalanced operation. These must be
removed before the tuner is used to tune an antenna fed with balanced feedline line.
A. Balanced feed line
(open wire, twin lead, or twin-axial line) is connected to the
BALANCED LINE
terminals on the left rear panel of the tuner (see Figure 2).
i. Loosen the wing nuts and remove the jumpers on the right side of the rear panel. Figure 2
shows the location of these jumpers with dashed lines. The jumpers may remain connected to
the ground terminal but make certain they cannot make contact with one of the connection
terminals on the fiberglass plate. See Figure 2.
ii. Connect your balanced feedline to the balanced line terminals located on the left side of the
rear panel. See Figure 2.
Note:
Route all single and random wire antennas safely to prevent RF burn hazard.
B. Coaxial
(un-balanced)
feedlines
connect to the coax connector labeled
ANTENNA.
Antennas
connected to the tuner with coax operate as unbalanced antennas. Two jumpers must be installed on
the rear panel for operation. These jumpers are installed at the MFJ Factory. Figure 2 indicates the
location of these jumpers with dashed lines on the right side of the rear panel.
C. Random Wire or Single Wire Line
fed antennas must be connected to the top balanced line terminal
located on the left of the rear panel as shown in Figure 2.
i. Connect a random or long wire to the top left terminal shown in figure 2.
ii. Connect the ground terminal to a suitable earth ground.
4.
A ground post is provided for an RF ground connection.
Transmitter
MFJ-976
50-ohm coax
To antenna
RF ground
CAUTION
Locate the tuner so the rear is not accessible during operation.
Figure 1
Block Diagram
