Topband: Effect of Radial Field on Antenna Impedance

[MICHAEL ST ANGELO]

Now that the leaves are off the trees and the cold weather has returned it's time to do antenna work.

I have an inverted L between two trees with 34 radials on the ground. Four radials are 135 feet long, the rest 70 feed long. I choose these lengths because they fit my yard. During the summer I keep the radials in the wooded area of my property in an arc of about 210 degrees. Once the leaves are off the trees I spread the radials into a full 360 degrees.
I normally measure the feed impedance with my N2PK VNA with requires lugging a laptop along with me. I built a  FA-VA5 Antenna Analyzer. While cumbersome to used standalone it is battery powered and quite handy.
My Inverted L is longer than a quarter wavelength on 160. I also use it on 80 meters and don't have to worry about matching a high impedance.
I wanted to see what effect changing the radial field diameter. I measured at the resonant frequency, 160 and 80 meters. Here are my results:

210 degree radial field:
Freq(MHz)  Rs    Xs
1.62     21.2  -1.7 (close to resonance)
1.8      30.7  +112
2.0      46.5  +237
3.5     111.0  -654
4.0      65.6  -346

360 degree radial field, relocated 7 radials.
Freq(MHz)  Rs    Xs
1.62     16.7  -5.6 (close to resonance)
1.8      23.6  +107
2.0      36.4  +233
3.5     124.0  -661
4.0      59.7  -351 

I wanted to move more radials but unfortunately they are stuck under a frozen leaf cover. I'll get to these when it warms up.

I was surprised that moving just a few radial made such a difference. 

Mike N2MS