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MFJ All Band Doublet                                                             Instruction Manual 

 
The earth ground should consist of at least one copper ground rod driven into 
the earth a minimum of 6 feet.  Multiple ground rods and  buried wires are 
superior to a single rod for lightning and RF protection.  160 meter operation 
requires special grounding considerations.  These considerations are discussed 
in the "160 Meter Operation" section.  
Never use woven flexible braiding for ground connections unless 

absolutely 

necessary

.  Braiding has high resistance to RF and lightning.  Copper flashing, 

wide copper foil, or large gauge solid copper wires are the proper materials for 
use in RF and lightning grounding applications.  Never ground the feedline on 
the antenna side of the balun.  
 
In-line coaxial lightning arrestors offer a minimal improvement in lightning 
protection.  The best method of protecting station equipment is to disconnect the 
feedline outside the building. 
 

TUNER REQUIREMENTS 

 
As noted earlier, this antenna requires an antenna tuner, ideally one that is able 
to tune balanced feedlines. If you have a tuner that tunes only unbalanced, 50-
ohm loads (such as the internal tuner in some transceivers) it is still possible to 
use this antenna. Connect a suitable 4-to-1 current balun (such as the 

MFJ-912

 

“W9INN Balun Box”) between your balanced feedline and your transceiver 
through a short piece of 50-ohm coax. 
 

TUNING THE ANTENNA 

 
This antenna comes with 100 feet of high-quality balanced feedline. In general 
any length of feedline will tune on all bands with this antenna. You may add 
more feedline if necessary to span the distance from your tuner to the antenna, 
or you may shorten the feedline if it is much too long (there is nothing magic 
about the 100 feet supplied). Should you find that it is impossible to tune your 
antenna on one or more bands, after you have exhausted the recommendations 
in your tuner manual, then try changing the length of the feedline, by adding or 
subtracting, say, five percent, or three to six feet, of feedline length. 
 
 
 

MAINTENANCE 

 

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