MFJ-939 Plug&Play IntelliTuner Automatic Antenna Tuner
Instruction Manual
2006-2015 MFJ Enterprises, Inc.
3
FAST START
WARNING
●
Never
operate the tuner with its cover removed. Contact with the components inside the
tuner while transmitting will result in painful RF burns.
●
Locate the tuner so that the rear terminals are
not accessible
during operation. The single
wire connection may have high voltage while transmitting.
●
Disconnect
all antennas from the tuner during lightning storms.
●
Always
tune with low power (2-20 watts). Apply maximum power only after tuning up.
●
Never
exceed tuner specifications.
1.
Connect the MFJ-939 to the interface cable and connect the interface cable to the radio.
2.
Check the radio instructions to verify that the radio can supply 750mA on the 12V line coming to the
interface cable. If the radio can not supply 750mA then connect a 12-15VDC power source capable of
supplying 750mA to the tuner.
3.
Connect your transmitter to the TRANSMITTER connector using a 50-ohm coaxial cable.
4.
Connect your coax-fed antenna to the ANTENNA connector using a 50-ohm coaxial cable, or
connect your random wire to the ANTENNA connector through the supplied adaptor.
5.
Connect your ground connection to the GROUND post.
6.
Press the [POWER] button to turn on the MFJ-939 tuner.
7.
Press the [ALT] button momentarily until there is one beep. One beep indicates that memory 1 is
selected.
8.
Key your transmitter to output a carrier of 2-20 watts CW, FM or AM.
9.
Press and hold the [TUNE] button for one second to start the automatic tuning process. When
completed, check to ensure an SWR of 1.5 or less has been achieved before increasing RF power.
Note:
If you have a tuning solution on one band and you then change bands and attempt to
transmit a tuning signal, the previous tuning solution may be sufficiently severe such that
no power is detected by the MFJ-939 (the MFJ-939 will tell you to increase power).
When this occurs, simply bypass the MFJ-939 and then initiate a tune.
10.
You are ready to transmit with full power.
Note:
During the automatic tuning process, the tuner will make some noise. These are the
relays switching at a very high rate and this is normal. Do not be alarmed.
Note:
When the tuner power is OFF, the tuner is in bypass mode and RF from the transmitter
goes directly to the antenna with no matching. The tuner also powers up in the bypass
mode. When the tuner power is ON, pressing [TUNE] quickly places the tuner in bypass
mode if desired, which is indicated by one beep.
Figure 1 General Setup
