[TowerTalk] Unequal Radial Currents

[Grant Saviers]

This (Sept/Oct 2020) issue of QEX has our (N7QT & me) article about our 
H40TT suitcase DXpedition vertical with a single coil loaded pair of 
75ft elevated radials for a top loaded helix wound vertical on (but 
unfortunately in the H40 case only near) the beach.  Not my idea, N6LF 
discusses it in detail in Antenna Compendium 6 for over/near salt water. 
Our coil was 22uH for 2x 75ft radials to resonate the pair.  N6LF also at
https://rudys.typepad.com/ant/files/antenna_vertical_short_radials.pdf

The modeling correlated well with the over the air performance 
comparison vs my T.

re the Weber article, read it, & don't get it.  N6LF in his QEX series 
shows the performance as elevated radial length is changed and shorter 
than 1/4wl is slightly better.  My modeling showed the asymmetry is 
small for 8 very unbalanced radials.  Even the single radial CrankIR 
shows about 3 db asymmetry, which we have used to favor a desired path.

Of course the more the earth is part of the current path, the lower the 
efficiency of the antenna.  With available space or transport 
constraints there are ways to get on the air on 160 at reasonable 
performance.

Grant KZ1W


On 8/29/2020 20:05, Robert Harmon wrote:
> I am very interested in the shortened radials hypothesis.  Has there been any documented testing of full length vs shortened radials done ?
> 
> Bob
> K6UJ
> 
> 
> 
>> On Aug 29, 2020, at 7:16 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
>>
>>
>>
>> On 8/29/2020 5:44 PM, Dennis W0JX via TowerTalk wrote:
>>> Unequal currents in 1/4 wave radials is to be expected primarily due to three factors: 1.) varying quality of the ground under each radial; 2.) the effect of close by objects such as buildings and other towers; and 3.) the variation in the length of the radial wires depending on type of wire, insulation, and construction methods. Effect on the actual radiation pattern depends, of course, on the severity of the current variation and the number of radials utilized.
>>> Dick Weber, K5IU, wrote a very informative article in the late 90's which was published in Communications Quarterly. He argued that 1/4 wave long radials were the poorest length on could use. He strongly recommended radial lengths of either 60-70 degrees (shortened) or 120 degrees long. These radials are tied together at a common point and fed either through a coil or a capacitor.
>>> W5UN had a very successful 4 square for 160 meters which used four, 96 foot long radials fed through a common coil. The radials were about 15 feet off the ground.
>>> Here at W0JX, I have four, 48 foot radials on my elevated 80 meter ground plane. The four radials come to a common point below the radiator and are tied to the coax shield through an inductor of approximately 3.3 uh. A big advantage of this arrangement is that I can resonate the antenna system by moving the tap on the radial loading coil. After many years of using full-sized radials, my on the air results tell me that the shortened radials are working better than the full size radials did.
>>> 73 Dennis W0JXMilan OH
>>
>> I'm not following the logic here.  If various radials have
>> unequal impedances, I don't see now tying them in parallel
>> though a coil or capacitor with magically make them have
>> equal currents.  Did Dick actually compare the currents in
>> the various configurations as built?  All I see are anecdotes,
>> not AB comparisons or measurements.
>>
>> Now if someone told me to use shortened or lengthened radials
>> and put individual coils or capacitors in series with each radial, then
>> I might believe the currents would be forced into equality.
>> Are you sure you got the story straight about Dick's article?
>> (I don't have access to it).
>>
>> 73
>> Rick N6RK
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