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@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@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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