Topband: Effect of Radial Field on Antenna Impedance

[Wes Stewart]

I'm not surprised and the results seem reasonable.

Wes  N7WS

On 12/8/2018 2:07 PM, MICHAEL ST ANGELO wrote:
> 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
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