From: WarmSpgs@aol.com
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Date: Fri, 23 Feb 2001 12:56:49 EST
Subject: Re: LF: RE: ANTS:  Higher L - higher ERP
To: rsgb_lf_group@blacksheep.org
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In a message dated 2/23/01 3:30:21 AM Eastern Standard Time, 
rik.strobbe@fys.kuleuven.ac.be writes:

<< I believe that the 'basic rule' with an elevated loading coil is that the
 current remains constant from the bottom end (feeding point) up to the coil
 and will drop linear from the coil toward the end of the antenna.
 So if you have the coil at the top of the vertical section you will get a
 constant current over this section, the same that you would get with a
 infinite topload (that is Andy's theory in other words ..) >>

That's a true enough rule of thumb, as far as it goes, but I'm doubtful of 
the "infinite topload" part.   We're talking about electrically very short 
antennae with top loading by means of inverted-L or T configurations, or 
other tophat capacitance sections.  The taper of the current distribution 
need not be all that significant to begin with, depending on the size of the 
top load section.  The key point is, with the systems many experimenters 
appear to be using, it's not enough by itself to account for the dramatic 
apparent difference in performance when one elevates the loading coil.

(In addition, even though you can resonate a system that has very small top 
capacitance and achieve a more constant current, the L/C ratio precludes the 
current from being the same as if it were a physically large top load.  No 
free lunch, in other words.)

You were perceptive in catching the current discrepancy.  I neglected to 
caution that my current readings were relative, not calibrated.  The 
"instrument" (it's a bit grandiose to call it that) was a toroid core 
transformer with a rectifier and DC microammeter that had at originally been 
calibrated at 50kHz.  I believe it had to be overstating the current 
significantly, for I am certainly not one of the fortunate LowFERs who lives 
atop open patches of 30milliSiemens/m soil either.  My best grounding efforts 
here have barely approached 90 ohms, so far as I can measure with a 
semi-accurate homebuilt impedance bridge.  With 12v and 83ma into the final, 
100ma or less would be the maximum likely current if the meter had been 
correct for absolute values.  It did track well with changes to the collector 
voltage of the final, however, so I believe it was reasonably linear over the 
part of the scale where it was being used.

Still, I'd love to see a reading in the multiple ampere range and to know it 
was real!

73,
John