Hi All,
Would this info be usefull ?
For a quater wave vertical "sitting" on the ground :
The 0dB reference is 4,1dBI for all.
4 radials 1/4wl long toa 24 degrees 0,96dBI
60 radials 1/4 wl long take off angle 23 degrees 2,6dBI
120 radials 1/2 wl long take off angle 28 degrees 2,8dBI
240 radials 1/4 wl long take off angle 28 degrees 3,0dBI
4 radials 2wl long take off anlge 24 degrees 0,98 dBI
60 radials 2wl long take off anlge 22 degrees 2,9dBI
120 radials 2wl long take off angle 20 degrees 3,6dBI
240 radials 2wl long, take off angle 17 degrees 4,1dBI
If you have a quater wave vertial over very poor ground changing the number from say 25 to 100 radials wont do much on the pattern.
If you go from 30 to 120 radials there is a improvement of 1dB
If you go from 5 to 120 radials there is a improvement of 3 dB.
Over good ground the improvement is sligthly less.
If you have <30 radials over very bad ground (city etc..) it has no use to lengthen them upto 2 wavelengths.
However with more radials it does become worthwill to extend the length to 2 wavelengths.
Where only a few radials are used < 10 the thickness of the radials becomes important.
With the thicker ones on the winning side.
When many are used it is less important as current is devided over all.
The impedance drops as the number of radials increases
approximently 50 ohms with 16 radials and 35 ohms with 120 radials.
POWER loss:
16 radials 0,1 wl long = 3dB
24 radials 0,125wl long = 2 dB
36 radials 0,15wl long = 1,5dB
60 radials 0,2wl long = 1 dB
90 radials 0,25wl long = 0,5 dB
120 radials 0,4wl long = almost 0 dB.
Now we almost never have the antenna sitting on the ground but often 30 feet or more in the air... By lifting the antenna the ground influence become less.
Attached you can find a few eznec plots giving the difference between a 1/4 wave length vertical with 3 or 60 1/4 wl radials at 0 or 30 feet.
Please dont take the given dB's as a fact...it is highly dependable on ground influence.
However the differnce between the number of radials is what you will get.
So overall.....
The more the better..
Only with a very large amount of radials it is usefull to extend them to 2 wavelengths.
If you can construct 60 radials 0,2wl you have about max reached..The only "noticable" improvment wich can ge made is lowering your tao with 5 degrees by using 240 radials 2wl long.
The best would to place the vertical over sea as that would be the perfect ground.
That is the reason why maritime mobile stations are always lound with only a small vertical.
Reference:
arrl antennabook
lowband DXing
rothammel
HF antenas for all location
Hope it helped.
73 Henry
19SD348
