[600MRG] Folded unipole antennas

[kl7aj at acsalaska.net]

I wish I could find all of Carl Smith's papers on this matter.   Carl Smith was the founder of Cleveland Institute of Electronics, and it was his work on directional AM antennas in the 1930s  that the FCC adopted as law.  He was also our consultant engineer at KJNP....who wisely encouraged us to use half wave towers....greatly increasing the stability of our pattern.

Anyway,..he also designed a whole lot of the Navy's VLF antennas and had some very unique ways of doing top hat loading AND elevated ground systems.   Anyway...if you can find any work by Carl Smith, it's worth reading.

Eric


On Thu, 26 Oct 2017 10:38:58 -0700, "Rudy Severns"  wrote:

>> The standard folded unipole antenna does not work when the height of the
>> antenna is substantially less than ¼-wave.  The reasons for this are
>> discussed in detail in chapter 4 (sections 4.2-4.6) in my antenna notes.
>> Even the presence of substantial top-loading does not fix the problem.  The
>> solution uses separate inductors in each downlead.  Again, this is all
>> carefully explained in my notes.
>> 
>>  
>> 
>> There have been a number of comments regarding sloping top-loading wires
>> reducing radiation resistance(Rr).  Sloping wires will have an opposing
>> vertical component of current which reduces the current moment of the
>> antenna, hence reducing Rr.  However, this effect is accompanied by a
>> reduction in tuning/loading inductor size and loss.  Initially the net
>> result is an improvement in efficiency as the sloping wires as made longer.
>> At some point, typically when 30-40% of the vertical is “shaded”, the
>> efficiency flattens out and then begins to decline as the wires are made
>> longer.  The flat region is very broad and not at all sensitive.  The
>> commercial boys worked all this out long ago.  On my web page there is an
>> article explaining this phenomena, look at my May/June 2013 QEX article,
>> Some Ideas For Short 160m Verticals.  The end of that article has an excerpt
>> from Carl Smith’s 1947 experimental exploration of this which clearly shows
>> the trade-offs at frequencies of interest to LF-MF operators.
>> 
>>  
>> 
>> GL and 73, Rudy N6LF
>> 
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