MFJ-993B IntelliTuner Automatic Antenna Tuner
Instruction Manual
©
2003-2005 MFJ Enterprises, Inc.
20
If more than 300 watts (or more than150 watts when 150 watts power level is selected) is applied to the
tuner, the tuner will go into bypass mode, flash
OVERLOAD
three times and send “QRT” (dah-dah-di-dah
di-dah-dit dah) on CW.
If the tuning process is activated under these conditions, the tuner will not start the tuning. It will indicate
the appropriate bounce code on the meter and display a warning message on the LCD.
Meter Needle Bounce Codes
(Meter needles bounce to the indicated mark until buttons are released.)
Forward
30 Watts Mark
100 Watts Mark
300 Watts Mark
Capacitor
Switches To
Transmitter Side
[2 beeps]
Insufficient Power to
Tune
(Forward < 2 Watts)
INCREASE POWER
[QRO]
Power Too High to Tune
(Forward > 125 Watts, or
Forward > 75 Watts and SWR > 3)
DECREASE POWER
[QRP]
Reflected
5 Watts Mark
20 Watts Mark
60 Watts Mark
Capacitor
Switches To
Antenna Side
[1 beep]
Bypass Mode
(L = 0 and C = 0)
[1 beep]
L or C at Its Limit During
Manual Adjustment
[1 beep at lower limit]
[2 beeps at upper limit]
Both Needles
30/5 Marks
100/20 Marks
300/60 Marks
Not Used
Not Used
Power Overload
(Forward > 300 or 150 Watts)
OVERLOAD
[QRT]
Table 3. Meter Needle Bounce Codes.
Foldback Circuit
Modern transceivers with solid-state finals usually have a foldback circuit to protect the final transistors
from high SWR, which can damage or destroy them. A foldback circuit detects the SWR during transmit
and reduces the output power as the SWR rises above a preset threshold, usually 2:1. The higher the
SWR the lower the power is set to prevent damage.
If your transceiver has a foldback circuit, you can simply key down and tune at any power level from 2 to
100 watts. If your transceiver does not have a foldback circuit, you must manually set the power level to
20 watts or less for tuning. At higher power levels, the reflected power occurred during tuning can
damage your transceiver and causes component arcing which can damage the relays in the tuner.
Check your transceiver owner's manual to see if yours has a foldback circuit.