MFJ MFJ-931 User Manual

MFJ-931 Instruc tion M anu al Artificial RF Ground

MFJ ARTIFICIAL GROUND

IMPORTANT: Please read entire manual before attempting to operate this

equipment. This unit does not provide a DC electric ground. A
separate wire will need to be run from the transmitter to an
electric ground if it is not already available.

Thank you for purchasing the MFJ-931 ARTIFICIAL GROUND. The MFJ-931 creates an
artificial ground with a random length of wire thrown on the floor. This produces a tuned
counterpoise. Also, the MFJ-931 will electrically place a far away RF ground directly at our rig.

INSTALLATION AND OPERATION

Creating Artificial Ground

Connect your transmitter of antenna tuner to the bind i n g post labeled "To Transmitter o r
Antenna Tuner Chassis Ground" on the back of the MFJ-931.

Note: This wire needs to be as short as possible, preferably with the ground posts as close as

possible i.e., the units side by side or one on top of the other.

Att ach th e length of ran dom wi re to t he red bi nding post labeled "To Counterpoise Wire or
Ground Connection Wire" on back of the MFJ-931. Be sure not to reverse these wires. The
random wire should be a quarter-wave length or less at the operating frequency. Be sure to
throw the random wire along the floor and to tape up the open end of the wire to avoid RF
burn.

To obtain maximum RF ground current for a low impedance RF ground, alternately adjust the
two controls on the front panel labeled "INDUCTANCE" and "CAPACITANCE". Turn the

INDUCTANCE control first until the highest amount of current can be registered on the built-in
AMMETER. Then adjust the CAPAC ITANCE control to increase the amount of RF current.
Try several inductance setting for best results. What if the needle goes off the scale or doesn't
move at all? Then the sensitivity of the Ammeter needs to b e ad jus ted . Tu rn the SE NS IT IVI TY
control until the needle is in the middle of the scale. Then readjust the INDUCTANCE control
for the highest amount of RF current and use the CAPACITANCE control to achieve
maximum RF current. If the nee dle is still off scale or zero, readjust the SENSITIVITY control
and repeat the tuning process

MFJ-931 Instruc tion M anu al Artificial RF Ground

until maximum RF current is achieved. After maximum RF current is reached, retune your
antenna tuner for minimum SWR. You may need to retune both the MFJ-931 and your
antenna tuner several times to achieve best results.

Electrically Placing Your Far Away RF Ground at Your Radio

Connect your transmitter or antenna tuner to the binding post labeled "To Transmitter or

Antenna Tuner Chassis Ground" on the back of the MFJ-931 with the shortest possible
wire(s). If necessary, place the MFJ-931 and your transmitter or antenna tuner side by si de o r
one on top of the other to insure the ground of each are as close to each other as possible.
Connect your existing ground wi r e t o t he red bi nd ing po st la beled "To Counterpoise Wire
or Ground Connection Wire" on the back of the MFJ-931. Do no t reverse these wires. After
making these connections, fol low the sam e procedure for

maximizing RF ground current as described in the

Creating Artificial Ground

section.
After maximum RF current is reached, retune your antenna tuner for mini mum SWR. You may
need to retune both your antenna tuner and the MFJ-931 several times to achieve best results.

WARNING: This unit does not provide a DC electric ground. A separate wir e will

need to be run from the transmitter to an electric ground if it is not
already available.