Today I finished burying the last radial on my 160M Inverted-L 4-square -
yippee! After an hour of relaxation, decided to study radial benefits for
my 80M K8UR style 4-Square for 80M - I know - I've been out in the sun too
long... For those not familiar with the K8UR style array, it is made from
4 phased sloping dipoles with the bottom tucked back to the tower.
The classic 4-Square has a better pattern but my K8UR array hangs nicely
over some large old oaks that are in the way for converting it to 4
verticals...
Part of what got me thinking and modeling was the feeling that the radial
field would need to be longer - it seems logical that the higher feedpoint
would see a bigger area... I also had the feeling that the benefit would
be less due also to the feedpoint being further from the ground...
I modeled a bunch of cases for each using AO and centering a single radial
field from the middle of each array to simplify the modeling. Based on
measurement results here and those quoted from W8JI, AO understates the
magnitude of ground losses but it is something any way. The cases studied
were radius lengths of 1/4, 1/2, 1 and 2 wavelengths each with a varying
number of radials. The results are tallied below. (The first column is
the number of radials modeled)
AO in fact predicts that a much bigger radial field is needed for the K8UR
array matching my intuition. The curve bends over after a 1/2 wavelength
for a classic 4-Square versus 1+ for the K8UR. What surprised me was that
AO actually predicted a bigger gain improvement for the K8UR array with
radials. AO predicts a gain of almost 3 dB going from a few radials to many
for the Classic and 4 for the K8UR.
Bottom line: Longer radial needs are yet another disadvantage for K8UR
style arrays versus Classic 4-Squares...
Tom Whiteside
N5TW Georgetown, TX
Classic
Radials 1/4 1/2 1/1 2/1
4 7.2 7.22 7.22 7.22
15 7.45 7.54 7.54 7.54
30 7.71 7.89 7.90 7.90
60 8.02 8.39 8.40 8.40
120 8.28 8.94 8.94 8.94
240 8.41 9.39 9.41 9.41
480 8.41 9.65 9.73 9.73
960 8.41 9.75 9.93 9.93
1920 8.41 9.79 10.03 10.03
K8UR
Radials 1/4 1/2 1/1 2/1
4 5.51 5.51 5.51 5.54
15 5.64 5.80 5.85 5.87
30 5.76 6.11 5.91 5.91
60 5.87 6.55 6.34 6.34
120 5.92 6.96 7.03 7.02
240 5.93 7.20 7.83 7.84
480 5.94 7.30 8.49 8.60
960 5.94 7.35 8.87 9.17
1920 5.94 7.35 9.03 9.57
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