HF9V Ground Plane Upgrade
by ik3umt
I was modelling various radiators over my groundplane.
I noted currents distribution thus radiation patterns
was so irregular due to radials interaction each other on different bands.
As previously seen , whole
radials system was completely detuned by radials closeness and proximity with
ground (about 10ft) so I decided to rebuild the system with 30 , equally
spaced, 33ft radials (eliminating 4
self-supporting ones for 6mt band).
This configuration, at least at computer modelling,
leads to an uniform radiation pattern in all
frequencies.
After modification, first thing that impressed me, as
detuning by ground proximity like previous seen, was the very light tuning frequency
deviation, on each of 9 bands.
Mostly on 80mt , where 2 quarterwave radials were removed, deviation was about some
tens KHz.
After usual tricky fine-tuning ( due
mostly to action points multitude and their slight interaction), values went
back where wanted also with surprising good 17m SWR curve.
This is the new SWR table as per MFJ 259B readings
including transmission line:
|
BAND |
|
F LOW |
R |
X |
SWR |
|
F MID |
R |
X |
SWR |
|
F HIGH |
R |
X |
SWR |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
80 |
|
3.500 |
58 |
16 |
1.4 |
|
3.508 |
38 |
0 |
1.2 |
|
3.525 |
21 |
0 |
2 |
|
40 |
|
7.000 |
41 |
13 |
1.4 |
|
7.047 |
32 |
0 |
1.3 |
|
7.128 |
28 |
12 |
2 |
|
30 |
|
10.100 |
36 |
7 |
1.4 |
|
10.122 |
33 |
0 |
1.4 |
|
10.150 |
29 |
0 |
1.5 |
|
20 |
|
14.000 |
55 |
16 |
1.3 |
|
14.120 |
57 |
12 |
1.3 |
|
14.350 |
61 |
19 |
1.5 |
|
17 |
|
18.068 |
51 |
20 |
1.5 |
|
18.135 |
67 |
0 |
1.3 |
|
18.168 |
63 |
10 |
1.3 |
|
15 |
|
21.000 |
36 |
0 |
1.2 |
|
21.140 |
38 |
0 |
1.2 |
|
24.450 |
35 |
0 |
1.3 |
|
12 |
|
24.890 |
60 |
7 |
1.2 |
|
24.920 |
65 |
0 |
1.2 |
|
24.990 |
70 |
17 |
1.5 |
|
10 |
|
28.000 |
38 |
0 |
1.1 |
|
28.240 |
45 |
0 |
1.0 |
|
29.000 |
34 |
7 |
1.5 |
|
6 |
|
50.000 |
36 |
14 |
1.8 |
|
50.800 |
47 |
2 |
1.0 |
|
51.000 |
44 |
4 |
1.1 |
With this arrangement, 10, 15 and 20 mt bands seem to be broader.
An objective valuation of improvement is difficult to
provide.
Surely 30 and mostly 40mt ( where
ground plane radius is a quarterwave ) seems to work
better.
On 80mt a good rule is valid ,
“many short radials are better than few long ones” , here 30 1/8 wave radials
are better than 2 qarterwave ones plus various
shorter lengths.
Remaining bands, however, benefit of groundplane uniformity as confirmed by first QSOs against pile-up without amplifier need.
Please feel free to contact me at ik3umt@ir3ip.net
73 de Federico
Ik3umt