TopBand: Radial current

Bob Wruble ai7b@teleport.com
Wed, 4 Jun 1997 17:12:16 -0700


the article was in communications qtrly by k5iu and contributions
and tests at jay, wx0b qth in dallas......good article and picked up
the rag at dayton rag seller booth   w7gg

----------
> From: Larry Tyree <n6tr@teleport.com>
> To: topband@contesting.com
> Subject: TopBand: Radial current
> Date: Wednesday, June 04, 1997 11:17 AM
> 
> 
> Gee - I had been feeling pretty good about my antenna system...
> 
> That was - until W0UN sent me a copy of a recent article he saw.
> 
> It seems likely that my 20 elevated radials aren't all equally sharing the
> current.  This article (sorry - I left it at home and forget who
> to credit as writing it) simply shows that if any one of the radials
> is near zero impedance (electrically a quarter wave) that the lion's
> share of the current will go into that radial.  
> 
> Compare the current into a zero ohm resistor and a 2 ohm resistor 
> and it becomes clear.
> 
> As you change frequency, the distribution of current in the
> radials will change as a different one approaches the right length.
> 
> The article also provides some solutions.  The simple approach appears
> to be to either shorten or lengthen all of the radials by a quarter
> wavelength (or something close to that).  Now, you will have impedances
> that still may vary by a few ohms, but none of them are near zero
> Ohms.  Then use some loading to tune the radial system for the desired
> frequency (using an inductor if they are short, or a capacitor in series
> if they are long).
> 
> This seems to make a lot of sense - and all from using nothing more
> complicated than Ohm's law.  
> 
> The advantages are a better pattern because of more uniform current
> flow.  The other advantage is elimination of a possible horizontal
> polarized component because of unequal distribution.  I didn't think
> of that before, but having symetric current flow around the base
> of the antenna is important in this regard.  It would also follow 
> that I need to be careful about the physical distribution of the 
> radials as well.  Currently, I have a higher concentration in 
> some directions (i.e., Europe and the east coast).
> 
> So - I guess I will cut my radials down in length (perhaps to 3/16 wave)
> and put an inductor in series with them and adjust it for minimum 
> impedance on 1825 kHz.  Perhaps I will make some current measurements
> before and after to verify the results.  I could tune each radial 
> individually to make them all the same impedance at 1825 before 
> connecting them in parallel.
> 
> Of course, this will remove all the magic from the system and it 
> will never work the same...  
> 
> Been trying a few CQs around 0500Z looking for a ZS or something,
> but no luck yet.  Received a QSL from HP3FL yesterday.  
> 
> 73 Tree N6TR
> tree@contesting.com
> 
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