Mobile Antenna Current Measurements at W8JI

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A sample of measurements above and below the loading coil with various antenna above the coil (current as percent of reference) follow: 

  Toroid with hat Small 2x2" coil with 24" hat up 24"  Long 12x3" coil with 24" hat up 24" Long 12x3"coil with 6' whip
Current below 100% 100 100 100
Current above 100 94.4 73 76%

 

  Toroid  with whip long 12x1.5" coil with 6' whip long 12x1.5" coil with 24" hat Small 2x2" coil with 6' whip 
Current below 100% 100 100 100
Current above coil 100% 79% 75% 96%
Current in whip 1ft above top of coil   73%    

The most revealing thing was how noticeably small changes in stray capacitance near the middle and top of the loading coil affect current distribution. It was quite evident hanging a large meter on each end of the coil would greatly perturb the system.