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COMPARISONS, BUT TUNERS EXPERIENCE THE HIGHEST RF CURRENT AND
MAXIMUM INDUCTANCE WITH SHORT ANTENNAS.  HIGHER VALUES OF MATCHING
INDUCTANCE CAN RESULT IN HIGHER LOSS DUE TO THE TYPICALLY LOWER Q
QUALITY FACTOR OF A PHYSICALLY SMALL, HIGHER VALUE INDUCTOR.  TO
DETERMINE TUNER LOSSES IN A FEW REAL WORLD CONDITIONS, I BUILT
ANTENNA SIMULATOR CIRCUITS BASED ON TWO DIFFERENT ANTENNA LENGTHS A
43 FOOT VERTICAL ON 80 METERS, AND AN 8 FOOT VERTICAL ON 40 METERS.
AS EXPECTED, I F PRODUCT REVIEW MFJ 9219 QRP TUNER, WATTMETER, AND
DUMMY LOAD REVIEWED BY PHIL SALAS, AD5X AD5X ARRL. NET  THE MFJ 9219
COMBINES AN ANTENNA TUNER, AN SWR/ WATTMETER, AND A DUMMY LOAD INTO
A COMPACT PACKAGE.  IT IS DESIGNED FOR PORTABLE OPERATION AT POWER
LEVELS UP TO 20 W.  MANY QRP LOW POWER TRANSCEIVERS AND KITS DO NOT
INCLUDE AN ANTENNA TUNER OR SWR METER, AND ANTENNA INSTALLATIONS IN
THE FIELD OFTEN REQUIRE COMPROMISES, SO THE MFJ 9219 IS A USEFUL
ACCESSORY.  OVERVIEW THE MFJ 9219S ANTENNA TUNER IS A STANDARD
MANUAL T TUNER SERIES CAPACITANCE/ SHUNT INDUCTANCE/ SERIES
CAPACITANCE.  THE TWO VARIABLE CAPACITORS HAVE VALUES OF 20 TO 650
PF, AND THERE ARE 12 SELECTABLE VALUES OF FIXED INDUCTANCE FROM 0R25
5H TO 6R5 5H.  THE WATTMETER IS ONLY FUNCTIONAL WHEN THE INTERNAL
DUMMY LOAD IS USED.  THE DUMMY LOAD CONSISTS OF EIGHT 2 W, SURFACE
MOUNT RESISTORS.  IT WILL HANDLE 5 W FOR SEVERAL MINUTES AT A TIME,
BUT IT IS LIMITED TO NO MORE THAN 10 SECONDS AT 20 W, AFTER WHICH IT
MUST BE PERMITTED TO COOL FOR AT LEAST 2 MINUTES.  THE TRANSCEIVER
INPUT RADIO IS A BNC CONNECTOR, AND THE OUTPUT ANTENNA CAN EITHER BE
COAXIAL ANOTHER BNC OR BANANA PLUGS FOR A RANDOM WIRE AND GROUND.
FIGURE 1 SHOWS THE INTERIOR OF THE UNIT.  THE MFJ 9219 SWR CIRCUIT
IS BASED ON THE WHEATSTONE BRIDGE, A SIMPLE CIRCUIT THAT CAN
DETERMINE UNKNOWN IMPEDANCES IN RF CIRCUITS.  THEORY OF OPERATION
FOR THE WHEATSTONE BRIDGE IS INCLUDED IN THE MFJ 9219 MANUAL,
AVAILABLE FROM MFJS WEBSITE, OR FROM EN. WIKIPEDIA. ORG/ WIKI/
WHEATSTONE BRIDGE.  BECAUSE IT IS A RESISTIVE BRIDGE, SOME TRANSMIT
POWER IS DISSIPATED IN THE BRIDGE DURING THE TUNING PROCESS WHEN
MEASURING SWR.  AN ADVANTAGE IS THAT YOUR TRANSMITTER IS PROTECTED
FROM HIGH SWR CONDITIONS WHILE TUNING, BECAUSE THE WORST SWR YOUR
TRANSMITTER CAN EVER SEE IS 2 1.  THE DISADVANTAGE IS THAT DURING
THE TUNING PROCESS, YOU CAN DISSIPATE UP TO 100 OF YOUR TUNE UP
POWER IN TWO OF THE THREE BRIDGE RESISTORS DURING HIGH SWR
CONDITIONS, ASSUMING YOUR TRANSMITTER CAN DELIVER FULL POWER INTO A
2 1 SWR.  OPERATING THE MFJ 9219 OPERATION OF THE MFJ 9219 CAN BE A
LITTLE CONFUSING AT FIRST.  THERE ARE THREE SWITCHES THAT NEED TO BE
USED IN THE PROPER MANNER.  THE TUNE/BYPASS SLIDE SWITCH PUTS THE T
TUNER IN SERIES WITH YOUR TRANSCEIVERS RF OUTPUT.  THE METER
ENABLE/OPERATE PUSHBUTTON SWITCH PLACES THE WHEATSTONE BRIDGE IN
SERIES WITH THE TRANSCEIVERS RF OUTPUT.  THE SWR/PWR PUSHBUTTON
SWITCH LETS YOU MEASURE SWR USED FOR TUNING OR RF POWER, USING THE
INTERNAL DUMMY LOAD WHEN THE METER ENABLE/OPERATE SWITCH IS IN THE
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