Vertical Antenna Ground Radial Loss Study

This document examines three published ground radial loss studies along with limited empirical data collected as a sanity test.

ARRL Antenna Book Ground Radial Loss

The ARRL Antenna Books use ground loss data compiled by John Stanley, K4ERO, using information from the book, Radio Broadcast Ground Systems, 1972, and first presented in the December, 1976, QST. The data in Table 1 is from two editions of the ARRL Antenna Book and are joined, at 36 radials. A 0.08 dB loss is added to merge with EZNEC data.

• 15th Edition ARRL Antenna Book, Page 3-13, Table 3
• 22nd Edition ARRL Antenna Book, Page 3-14, Figure 3.27

K3LC EZNEC4 Models

Al Christman, K3LC, used EZNEC4 to model a variety of radial ground systems. The results are published in the document Maximum-Gain Radial Ground Systems for Vertical Antennas, 2004. Table 2 and Table 3 are loss data for 40 and 160 Meter vertical antennas over average soil. The data is normalized to a 1.79 dBi zero ground loss vertical antenna.

N6LF Vertical Antenna Ground Systems

Rudy Severns, N6LF, revisited previous studies and published his results in Vertical Antenna Ground Systems At HF. The results for 160 Meters over average ground are summarized in Table 4.

KN5L 20 Meter Vertical Measurements

A 20 meter vertical consisting of 8" #14 wire and 16.5'x1" aluminum pole was measured against three sets of ground radials is shown in Figure 1. Measurements were taken at the antenna using a FG-01 Antenna Analyzer. EZNEC is used to solve the ground loss by adding load resistance such that the model matches the antenna measured impedance. The EZNEC 2D plot is used to evaluate antenna loss. The results are summarized in Table 5.

Figure 1 - KN5L 20 Meter Vertical Antenna Ground Radials

Evaluating Ground Loss Data

The graph in Figure 2 plots the four sets of ground loss data. The ARRL Antenna Book and K3LC 40 Meter plots have a close match from 24 to 100 radials. The ARRL data below 24 radials is suspect. The K3LC 160 Meter and N6LF plots are a close match. The KN5L empirical data is reasonably close to the ARRL and K3LC published data. Two "LINE" lines are added as a guide for average 40 and 160 Meter ground radials.

Figure 2 - Ground Radial Loss

Ground Loss Values

The two "LINE" lines in the above plot can be used to compute ground loss values, summarized in Table 6 and Table 7, for use in EZNEC modeling using the directions in the EZNEC manual in the section beginning with:

• The third approach is to use MININEC-type ground, which models the ground reflection but not the conductive loss, and simply add a resistive load at the feedpoint to simulate the radial system loss resistance.

EZNEC Antenna Evaluation

The EZNEC 2D Plot below evaluates five 20 Meter antennas is shown in Figure 3. All models use the same MININEC-type ground.

• Primary: Inverted Vee at 40 feet elevation.
• BPverticalDipole: Vertical base at 19 feet, Buddipole: 2 x 22" arms, coil 1.6 uH, and 9.5' whip with four 1/4 wave Radials at 45 degree downwards slope.
• GroundVertical60Radials: Ground mounted 1/4 wavelength vertical with 60 on ground radials. 8.2 Ohm ground loss.
• GroundVertical8Radials: Ground mounted 1/4 wavelength vertical with eight on ground radials. 42 Ohm ground loss.
• ShortGroundVertical8Radials: Ground mounted 0.1 wavelength vertical with center loading and eight on ground radials. 42 Ohm ground loss.

Figure 3 - EZNEC 2D Plot

Ground Radial Length

The minimum ground radial wavelengths suggested by K4ERO and K3LC are plotted in Figure 4.

Figure 4 - Minimum Ground Radial Length