Aloha, Jim K9YC brings up some great points.
Jeff, your 130' sloping vertical could work better configured as a ground
plane with 2, 3, 4 or more symmetrical, elevated counterpoise wires. NH6V
and I use a similar portable top band antenna we use three times a years.
It's a 130' at 45 deg. wire sloping to a 140' tree. The counterpoise
consists of two opposing radial wires run parallel to and 25' from the
ocean.
EZNEC modeling can lead us to counterpoise wire lengths that present the
lowest impedance which cuts down the work that the feedline common-mode
choke must do. If this interests you I will post wire lengths and
common-mode choke construction. The container is no longer a part of the
antenna system.
The paper by Rudy, N5LF, *Experimental Determination of Ground System
Performance for HF Verticals Part 3 Comparisons Between Ground Surface and
Elevated Radials *
https://www.antennasbyn6lf.com/ARRL_articles/QEX%20Mar-Apr%202009%20Ground%20systems%20part-3.pdf
Dave KH6AQ (we will see you all in the Big Stew next week...)
On Thu, Dec 18, 2025 at 9:58 AM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 12/18/2025 7:35 AM, Radio KH6O wrote:
> > Grounding rods will be driven in at each corner.
>
> The earth is a big resistor. The only function of ground rods on
> transmitting antennas is lightning protection. They do NOT make
> transmitting antennas work better.
>
> The functions of radials is NOT to couple to earth, but rather to SHIELD
> the antenna's field from it, and to provide a low impedance return for
> antenna current -- that is, they are the other half of the antenna.
>
> I agree with KH6AQ's advice. And I suggest that you read my piece about
> 160M radial systems, which is really a compilation of great engineering
> work by others on the topic.
> http://k9yc.com/160MPacificon.pdf
>
> Even better, go to the most important source, Rudy Severns, N6LF.
> https://www.antennasbyn6lf.com/
>
> Rudy lit the big lightbulb for me about radial systems and loss. He
> analyzed radial systems by studying the distribution on them of the
> antenna's return current. Several important takaways.
>
> 1) That current divides between them numerically. The closer they are to
> the earth, the more current they induce in the earth, which shows up in
> each radial as series resistance. The loss in each is I squared R, where
> R is that loss coupled R. The total loss in the radial systems is the
> sum of I squared R numbers.
>
> 2) As we increase the number of radials, current in each is
> proportionally less, but LOSS in each is reduced by the SQUARE of the
> number of radials. THAT'S why more is better!
>
> 3) Each radial exhibits the same current distribution as any other part
> of an antenna.
>
> 4) An antenna will be lengthened (that is, VF less than 1) by close
> proximity to the earth. For example, I've measured VF on the order of
> 0.75 on 160M for radials laying on the ground at my QTH in the Santa
> Cruz Mountains (poor soil, very rocky). SO -- at my QTH, a quarter-wave
> on-ground radial is about 100 ft.
>
> 5) Current distribution on antenna elements is determined by length, and
> must be near zero at the far end. An antenna (that radial) longer than a
> quarter wave but shorter than a half wave will result in a peak value of
> current along it that is greater than at the feedpoint, which can
> increase the loss coupled from the earth. Rudy recommends that radials
> be slightly shorter than a quarter wave.
>
> 6) #2 and #5 are why, when space is limited or "stuff" limits their
> length in some directions, a lot of radials shorter than a quarter-wave
> can be an effective counterpoise (return for antenna current).
>
>
> 73, Jim K9YC
>
>
>
>
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