Control Head Theory And Operation; Control Head Power - MFJ Super Hi-Q Loop Instruction Manual

MFJ Super Hi-Q Loop™ Antenna Instruction Manual

CONTROL HEAD THEORY AND OPERATION

The MFJ "Super Hi-Q Loop" control head contains a cross needle SWR-WATTMETER that reads
forward and reflected power on high and low power scales. The high power scales are 300 watts
forward and 60 watts reflected, and the low power scales are 30 watts forward and 6 watts reflected.
Power is always read from the top scale with a 0.1 multiplier in low power.
The control head supplies control voltages to the loop antenna through the coaxial feedline. These
voltages are low voltage and low current so that the length of the coaxial line does not affect the
operation of the motor. It is important that the feedline remain water-free and that there are no short
circuits between the center conductor and the shield of the feedline.
The control head also contains the circuits that detect the tuning condition of the antenna. These
circuits are activated only when the AUTO BAND SELECT "UP" or "DOWN" buttons are depressed.
When these switches are "latched" in the presence of constant RF, the loop will tune until the SWR
drops or the end of the tuning range is met. If the SWR minimum is crossed a "beeper" sounds and the
motor voltage is removed. If the end of range is reached without crossing the SWR minimum the
FREQ "UP" or "DOWN" LED will extinguish and the motor will stop. When you release the "latched"
button after the low SWR point is crossed a "MOVE" LED near the "FINE TUNE" buttons will be lit.
The control head also contains circuits that allow the motor to move in slow steps. To optimize the
SWR the FINE TUNE buttons are used. The "MOVE" LED's that indicated which way you needed to
move after using the AUTO BAND SELECT will extinguish after the proper FINE TUNE button is
pressed.
Additionally, there are switches for wattmeter power sensitivity, the meter lamp, and main power off-
on. There are also two yellow LED's labeled "FREQ" UP and DOWN that monitor the current that the
loop motor (feedline) is drawing. A continuous light indicates that one of the "AUTO BAND
SELECT" switches is on and the motor is running, a flashing LED indicates that a FINE TUNE switch
is on. These LED's should NOT remain lit after the motor reaches a stop. This condition should occur
in less than 40 seconds of fast tuning.

CONTROL HEAD POWER

The MFJ "Super Hi-Q Loop" control head requires a 9-15 VDC, ungrounded power supply. The
power jack accepts a 2.1mm coaxial plug with the center conductor positive. The MFJ-1312B is
supplied for 110 Vac operation. For 220 volt operation the MFJ-1315X is available. Connect the
power adapter into the power jack on the back of the control head. There is also an internal battery
connection that can be used with 2 battery holders with 4 "AA" batteries in each for portable operation.
CAUTION: Do not use any grounded external power supply to power the control head. Use
the AC adapter supplied with the unit.
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