‰  NOW 40 WPM  ‰  TEXT IS FROM AUGUST 2012 QST  PAGE 48‰
HAVE BEEN LIMITED TO BAREFOOT OPERATION WITH THE REMOTE AUTO TUNERS
AVAILABLE.  NOW, WITH THE INTRODUCTION OF THE MFJ 994BRT AND MFJ 998RT HIGH
POWER REMOTE AUTO TUNERS, WE CAN REALIZE THESE BENEFITS WHEN USING A HIGH
POWER AMPLIFIER.  THE MFJ 994BRT WORKS WELL WITH MEDIUM POWER HF AMPLIFIERS
FEEDING LESS THAN PERFECT ANTENNA SYSTEMS.  BUT IF YOU ARE RUNNING MORE
THAN 600 W OR PLAN TO DO SO IN THE FUTURE, THE MFJ 998RT IS THE WAY TO GO.
PRODUCT UPDATE SINCE THESE REVIEW UNITS 

HIGH IMPEDANCE TUNING RANGE IS SIGNIFICANTLY BROADER THAN THE LOW IMPEDANCE
RANGE.  THE LOW IMPEDANCE LIMIT IS SPECIFIED AT 4 1 SWR.  I MEASURED THE
MFJ 998RT TUNER LOSSES USING THE 160 AND 80 METER SHORT ANTENNA SIMULATOR
CIRCUITS DESCRIBED EARLIER, AGAIN WITH APPROXIMATELY 10 OF REAL RESISTANCE
ADDED TO SIMULATE GROUND LOSSES.  THE MFJ998RT WAS ABLE TO MATCH A
SIMULATED 43 FOOT VERTICAL FOR 80 METERS AND A SIMULATED 90 FOOT ANTENNA
FOR 160 METERS WITH POWER LOSS LESS THAN 10 AND MINIMUM SWR OF 1R2 1 ON 80
AND 1R6 1 ON 160.  OPEN/SHORT CIRCUIT TESTING IDEALLY A TUNER SHOULD NOT BE
ABLE TO MATCH AN OPEN OR SHORT CIRCUIT LOAD.  IF IT DOES, THIS MEANS THAT
IT IS TUNING INTO ITS OWN INTERNAL LOSSES.  HOWEVER, NO ANTENNA TUNER IS
LOSSLESS DUE TO COMPONENTS WITH FINITE Q.  FROM PAST EXPERIENCE IVE FOUND
THAT MOST ANTENNA TUNERS MANUAL AND AUTOMATIC CAN FIND A MATCH ON ONE OR
MORE FREQUENCIES WHEN CONNECTED TO AN OPEN OR A SHORT.  IN THE ARRL LAB,
NEITHER TUNER COULD FIND A MATCH INTO AN OPEN CIRCUIT OR A SHORTED PL 259
CONNECTOR.  AT MY STATION, I FOUND SOME NOTEWORTHY SHORT CIRCUIT MATCH
OCCURRENCES.  WITH BOTH THE MFJ 994BRT AND MFJ998RT, ON 20 METERS I FOUND A

MFJ 994BRT REMOTE AUTO TUNER THE MFJ 994BRT, WITH ITS 600 W SSB/CW
CAPABILITY, IS PERFECT FOR THE MANY MEDIUM POWER AMPLIFIERS ON THE MARKET.
THE PHOTOS ACCOMPANYING TABLE 2 SHOW THE OUTSIDE OF THE UNIT AND THE
INTERNAL CIRCUITRY.  NOTE THAT THE INDUCTORS CONSIST OF A MIX OF TOROIDAL
AND WIDE SPACED AIR WOUND INDUCTORS.  ARRL LAB TEST RESULTS ARE GIVEN IN
TABLE 2 AS YOU CAN SEE, THE MFJ 994BRT MATCHED ALL RESISTIVE LOADS
PRESENTED TO IT THAT WERE WITHIN ITS SPECIFIED TUNING RANGE.  AND WHILE
THERE WERE A FEW CASES IN WHICH THE SWR DIDNT REACH THE 1R5 1 TARGET, IN
MOST CASES THE TARGET SPECIFICATION WAS MET.  I MEASURED THE MFJ 994BRT
TUNER LOSSES USING THE 160 AND 80 METER SHORT ANTENNA SIMULATOR CIRCUITS
DESCRIBED EARLIER.  APPROXIMATELY 10 OF REAL RESISTANCE WAS ADDED TO
SIMULATE GROUND LOSSES.  THE MFJ 994BRT WAS ABLE TO MATCH A SIMULATED 43
FOOT VERTICAL FOR 80 METERS AND A SIMULATED 100 FOOT ANTENNA FOR 160 METERS
WITH POWER LOSS LESS THAN 10 AND MINIMUM SWR OF 1R3 1 ON 80 AND 1R7 1 ON
160.  MFJ 998RT REMOTE AUTO TUNER THE MFJ 998RT HANDLES A FULL 1500 W PEP
ON SSB OR CW.  CONSTRUCTION IS SIMILAR TO THE MFJ 994BRT WITH A MIX OF
TOROIDAL AND WIDE SPACED AIR WOUND INDUCTORS.  TABLE 3 SHOWS THE RESULTS OF
RESISTIVE LOAD TUNING RANGE AND LOSS MEASUREMENTS IN THE ARRL LAB.  IN MOST
CASES THE 1R5 1 TARGET SPECIFICATION WAS MET.  AS WITH THE MFJ994BRT, THE
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ