Topband: K2AV Counterpoise

[k8bhz at alphacomm.net]

1): The length to avoid is nothing more than a half wavelength, which 
translates the same impedance from end to end. i.e., the high Z open end 
translates to a high Z antenna base end. This results in minimum radial 
current. At 10' up, they're close to free space (0.47 vs 0.5 WL). At 2" 
above the ground, the length to avoid is still a half wave, but 
shortened by the near ground velocity number. Your 2" high length is 
almost identical to my on ground one. Very good correlation....

2): Rudy's original premise exactly. If the radials are the same 
dimension as the short vertical, you achieve 90% of the performance 
possible. I merely resonated them exactly, to achieve the lowest radial 
impedance. The dimension similarity was purely serendipitous...Sometimes 
you win!

Brian  K8BHZ
> Two things become obvious:
>
> 1) As the radial height is lowered the "length to avoid" gets shorter.  When the radials are at 10 ft the large drop in efficiency happens at a radial length of ~0.47 WL (~250 ft at 1.85 MHz).  When the radials are at 2 inches the efficiency dip happens at a radial length of ~0.36 WL (~191 ft).
>
> 2) For both the straight vertical and the inverted L, the highest efficiency happens at a radial length of ~0.2 WL (~106 ft).  But if you make them shorter, say the length of the vertical portion of the inverted L (60 ft, ~0.11 WL), you're really not giving up very much.
>