Topband: 1/4 wave 160M wire antenna

[Jim Brown]

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