FIRST WE WENT TO THE STOCK SHELF AND PULLED DOWN A 6M5X.
THE SHOP CREW ASSEMBLED THE ANTENNA IN ABOUT 20 MINUTES AND INFORMED MIKE STAAL, K6MYC OUR ENGINEER THE ANTENNA WAS READY TO TEST. IT WAS PUT ON A 2" DIAMETER MAST TEST STAND AT 42 INCHES ABOVE GROUND AND THE BALUN AND SHORTING BARS INSTALLED.

FOR OUR SWR MEASUREMENTS WE USE A PROFESSIONAL TELONIC BRIDGE CALLED A RHOTECTOR AND A WAVETEK RF SWEEP GENERATOR. THE RHOTECTOR USES TWO PORTS IN A BALANCED BRIDGE CONFIGURATION. WHEN BOTH PORTS AR TERMINATED WITH HP OR WEINCHEL CALIBRATED 50 OHM TERMINATIONS, THE DETECTED OUTPUT IS ZERO. NEXT WE TERMINATE ONE PORT WITH A CALIBRATED MISMATCH LIKE 1.2:1. WE USE A LARGE 10" OSCILLOSCOPE TO DISPLAY THE SWEPT DETECTED OUTPUT AND WITH A 1.2:2 MISMATCH ON THE ROTECTOR, WE SET THE SCOPE GAIN SO AS TO PRODUCE A TRACE REPRESENTING 1.2:1 ONE DIVISION ABOVE BASELINE ACROSS THE FACE OF THE SCOPE. FOUR DIVISIONS UP IS 1.5:1 AND 8-12 DIVISIONS UP IS 2:1. NOW WE SUBSTITUTE THE ANTENNA FOR THE CALIBRATED MISMATCH AND WE ARE READY TO GO.

THE SWEEPER HAS 100, 50, 10 and 1 MARKERS SO WE CAN CALIBRATE THE FACE OF THE SCOPE SO ONE VERTICAL DIVISION EQUALS 100 KHZ AND WE SET 50.0 MHZ IN THE MIDDLE OF THE SCREEN.

FIRST WITH THE ANTENNA AT 42 INCHES ABOVE THE GROUND THE RHOTECTOR WAS ATTACHED AND THE VSWR CURVE SHOWED AN '' APPARENT MATCH FREQUENCY" AT 49.85 MHZ. THIS UNDESIRABLE SWR READING HAS BEEN NOTED IN THE FIELD BY CUSTOMERS AND IT IS A RESULT OF PROXIMITY TO GROUND OR OTHER OBJECTS. EACH OBJECT MIGHT PRODUCE A DIFFERENT SWR CURVE AND A DIFFERENT "APPARENT MATCH FREQUENCY"

NOTICE I STAY AWAY FROM THE TERM "RESONANCE". THIS "APPARENT 50 OHM MATCH FREQUENCY" IS JUST THAT, APPARENT. IT IS JUST WHERE THE ANTENNA FEED POINT "LOOKS LIKE 50 OHMS BUT BEARS LITTLE RELATIONSHIP TO THE REAL RESONANCE. BUT THAT SUBJECT IS ANOTHER STORY COMPLETELY.

NOW BACK TO THE ANTENNA. WE RAISED THE ANTENNA TO ABOUT 10 FEET FOR THE WETTING SETS AND THE VSWR CURVE AT THAT HEIGHT WAS ALMOST IDENTICAL WITH THE CURVE SHOWN ON THE DIMENSION SHEET IN THE CUSTOMER MANUAL. THE BEST MATCH (1:1 IN THIS CASE) OCCURRED AT 50.175 AND THE MANUAL SHOWED 50.225. NO CHANGE FROM FACTORY SETTING WERE TRIED.

THE TEST WAS DONE IN SEVERAL STAGES.
1. WETTING JUST THE DIRECTORS ONLY NETTED A DOWN SHIFT IN FREQUENCY OF LESS THAN 50 KHZ.
2. THEN THE DRIVEN ELEMENT AND THE DIRECTORS WERE WETTED LESS THE AREA INSIDE THE SHORTING BARS AROUND THE 'T' MATCH.AND THIS CAUSED THE WORST SHIFT DOWN (200 KHZ).
3. NEXT THE ENTIRE ANTENNA WAS WETTED AGAIN EXCEPT FOR THE 'T' MATCH. THIS CAUSED THE MATCH TO LIFT OFF 1:1 AT 49.9 MHZ AND GO TO 1.2:1 AT 49.9 AND 1.3: 1 AT 50.0 MHZ
IT IS ALSO WAS STILL ONLY 1.6:1 AT 50. 200 (VERY ACCEPTABLE)

4. FINALLY THE WHOLE ANTENNA WAS WETTED INCLUDING THE 'T' MATCH AREA. NO NOTICIBLE MATCH DETERIORATION OCCURRED FROM STEP 3 WITH THIS FINAL WETTING. IF ANYTHING THE MATCH CAME UP A BIT IN FREQUENCY AND THE RESIDUAL 1.2:1 RETURNED TO BASE LINE

AT NO TIME IN THE TESTS DID THE MATCH EVER EXCEED 2:1 AT 50.200
WHILE THIS IS A BIT HIGH AND MAY CAUSE SOME OUTPUT CUTBACK OF SOME TRANCEIVERS, NOTHING IS FORCING OPERATION AT OR ABOVE 50.2 MHZ.
IT SHOULD BE NOTED THAT ANY WIND MOVEMENT OF THE ANTENNA DURING THESE TESTS WOULD KNOCK A FEW DROPS OFF THE DRIVEN ELEMENT AND THE MATCH WOULD INSTANTLY GO TO 1:1 AT 50 MHZ.

TWO CONCLUSIONS COME OUT OF THESE TESTS. IF YOUR "IN BAND" MATCH GETS WORSE THAN WHAT WE CAN PRODUCE, YOU HAVE DIFFERENT KIND OF WATER THAN MOST OF US. OR...YOU HAVE STARTED WITH A LOWER MATCH FREQUENCY THAN YOU SHOULD HAVE. THIS CAN AND DOES OCCUR DUE TO ANTENNA PROXIMITY TO GROUND, OTHER LARGE OBJECTS LIKE ROOFS, BUILDINGS OR VERY WET TREES A FEW FEET AWAY OR YOUR 'APPARENT MATCH FREQUENCY" IS BEING SHIFTED BY: AMPLIFIER CIRCUITS AND RELAYS, EXTERNAL SWITCHES, MEASUREMENT EQUIPMENT OR FEEDLINE PROBLEMS DUE TO LOSS OR IMPEDANCE VARIATION. SO MANY THINGS CAN AFFECT YOUR 'APPARRENT MATCH FREQUENCY" THAT YOU MUST ASSUME THAT SOMETHING IS CHANGING IT FROM WHAT WE MEASURE AT THE RANGE.

CLEARLY THE CAUSE OF ANY SHIFT IS BECAUSE THE ANTENNA IS A CRITICALLY TUNED, HIGH GAIN YAGI WITH A VERY LOW FEED IMPEDANCE. THE GAIN CURVE IN THIS DESIGN PEAKS BETWEEN 50.200 AND 50.300 BUT IS ONLY DOWN .06 DB AT 50.000 AND 50.400 MHZ SO EVEN IF ALL THE WORKING PARAMETERS OF THE ANTENNA SHIFTED DOWN 200 KHZ, YOUR GAIN WOULD ONLY DROP BY .06 DB. AT 50.1 MHZ.

THE MOST TOUCHY SECTION IS CLEARLY THE DRIVEN ELEMENT TIPS. ANY DIELECTRIC NEAR OR ON THE TIP OF THE ELEMENT WILL DRIVE THE FREQUENCY DOWNWARD. EVEN A PLASTIC CAP OVER THE END WILL HAVE THAT EFFECT. WATER IS A DIELECTRIC. THE RAIN OR WATER DROPS ALSO INCREASE THE DIAMETER OF THE ELEMENT MAKING IT GO EVEN LOWER IN FREQUENCY. IF THE DIAMETER OF THE DRIVEN ELEMENT WERE LARGER, WATER WOULD HAVE LESS EFFECT. WIND AREA AND COST WOULD GO UP UNFORTUNATELY. ENGINEERING WILL LOOK INTO JUST INCREASING THE EFFECTIVE TIP DIAMETER OF THE DRIVEN ELEMENT TO REDUCE THIS EFFECT. RESULTS OF THESE TEST WILL BE ANNOUNCED FOR THOSE OF YOU WHO NEED HELP IN THIS AREA.

THE RESULTS FOR THE 6M7JHV WOULD BE SIMILAR OR SLIGHTLY LESS SINCE IT IS A WIDERBAND ANTENNA.