[TowerTalk] Unequal Radial Currents

[Robert Harmon]

Hi Jeff, 

Thanks for sharing your experience with shortened radials.  This is music to my ears.  I don't have enough real estate to install 1/4 wave radials so if I can do shortened radials and not sacrifice efficiency that would be super.  There must have been some research done with A/B testing of longer vs shortened radials.  Rudy, N6LF has researched/tested elevated radials at different heights above ground and is a good resource for that, I wonder if he has done any testing of shortened radials ?  Need to find out...........   Inquiring minds want know, hihi.  

Bob
K6UJ




> On Aug 29, 2020, at 8:20 PM, Jeff Blaine <KeepWalking188 at ac0c.com> wrote:
> 
> I've used shortened elevated radials in a few projects.  Made sense to me - but anyone who knows me will confirm I'm not the sharpest knife in the drawer.
> 
> Started out with radials that were a bit short - 5-10% - forget exactly.  Verts was constructed and radials hung but built a bit long.  Then trimme each radial - one at a time.  The VNA was connected between the fixed vertical and attaching one radial. Measured the resonant frequency of the first one - which determined the benchmark.  Disconnected that radial, repeated with the next radial, trimming to length to match the benchmark resonant frequency.  Continued with all radials, one at a time. Then connected 'em all together.  The vertical final trim frequency was made by adjusting the vertical length slightly (if you use a small coil in series with the vert that makes adjustment of the frequency a lot easier than raise/lower, repeat).
> 
> It was fun and gave me a sense of precision while using my shiny cool toys.  No idea if it really made a big difference as there was no really good way to do a before/after comparison.  The resulting verticals and 4-square arrays "worked" in the classic sense.
> 
> There some amount of modeling and discussion of choices out on my web page under prior antennas (40m 4sq and 80/160m vert) for those looking for some late night reading.
> 
> 73/jeff/ac0c
> alpha-charlie-zero-charlie
> www.ac0c.com
> 
> 
> On 8/29/20 10:05 PM, 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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