160-meter Ground Connection Resistance at W8JI
Clay soil, dry conditions, 20-foot tall hat element resonant on 160 meters. All radials 50 ft long except for test radial, which is 1/4 wl electrical insulated counterpoise.
|
Ground |
Ground Resistance Ω |
Antenna Resonance MHz |
System change with resonant test radial |
System change adding one additional rod |
|
Two 5’ rods |
85 |
1.944 |
Large over 50% |
Rod has large effect |
|
One radial NE |
80 |
1.905 |
Large |
Rod has large effect |
|
One radial SE |
80 |
1.905 |
Large |
Rod has large effect |
|
One radial NW |
77 |
1.931 |
Large |
Rod has large effect |
|
Four radials |
42 |
1.819 |
Moderate 50% |
Rod has large effect |
|
Three radials and two rods |
50 |
1.819 |
Moderate 50% |
Rod has moderate effect |
|
Four radials three rods |
54 |
1.820 |
Low 25% |
Rod has noticeable but small effect |
|
Seven radials three rods |
29 |
1.875 |
Very low <10% |
Rod makes very little difference |
|
Eight radials three rods |
27 |
1.880 |
Very low |
Rod makes very little difference |
Performance Indications of Test
Ground systems are reactive. Poor grounds can add reactance. This is shown by the resonant frequency shift as the ground system is altered.
In slightly moist clay pastureland soil it takes about 8 short (1/8th wl) radials to stabilize the ground impedance.
In slightly moist clay pastureland soil, two or three rods make a poor RF ground for low impedance antennas.
If you use four short radials on a vertical, it is almost like no ground at all.
With small radial systems, ground rods can actually increase feed resistance. Use this particular phenomena with some caution, since I did not sweep frequency!