‰  NOW 25 WPM  ‰  TEXT IS FROM SEPTEMBER 2012 QST  PAGE 49‰

ANTENNA IS INSTALLED NOT FAR ABOVE A WOOD AND COMPOSITION SHINGLE ROOF.  I
FOUND THIS AFFECTED THE TUNING OF THE ANTENNA ON 20 METERS QUITE A BIT.
THE INITIAL FREQUENCIES OF MINIMUM SWR WERE ABOUT 200 KHZ LOWER THAN
EXPECTED ALTHOUGH HIGHER FREQUENCY BANDS WERE LESS AFFECTED.  AFTER SOME
CONVERSATION WITH TOM, N6BT, A FIELD READJUSTMENT PROCEDURE WAS CREATED AND
HAS BEEN ADDED TO THE MANUAL ALONG WITH AN EXPLANATION OF THE CIRCUMSTANCES
THAT AFFECT ELEMENT TUNING.  IN GENERAL, ANY ANTENNA WITH A STANDOFF
DISTANCE OF LESS THAN 1/4 WAVELENGTH FROM OTHER ANTENNAS OR SURFACES WILL
BE DETUNED COMPARED TO THE SAME ANTENNA MOUNTED IN THE CLEAR.  THIS IS
PARTICULARLY TRUE FOR YAGIS AND OTHER PARASITIC ARRAYS THAT ARE HIGHLY
DEPENDENT ON COUPLING.  BACK ON THE ROOF, AND STARTING WITH THE AS
DELIVERED ELEMENT LENGTHS AND COIL CONFIGURATION, I WAS ABLE TO RAISE THE
20 METER RESONANT FREQUENCIES EASILY BY ADJUSTING ELEMENT LENGTHS AND THE
‰  END OF 25 WPM TEXT  ‰  QST DE W1AW  ƒ