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