I finished the installation of 80m 4SQ last week. I have full size aluminum
verticals guyed with ropes and elevated about 3m from ground. Each vertical
has one tuned elevated radial (in line with the diagonals away from the
centre) and I use Comtek box for phasing. Verticals are 1/4 wl from each
other and they as well as radials are also exactly 1/4wl - 20.5 meters long.
I have two questions:
1. I plan to install a ground screen on the ground below the antenna. Probably
about 60 radials on ground per vertical. What kind of wire is good for such
passive ground screen (not electrically connected to the antenna). I am
sure Cu, CuFe, Al would be fine. But would Fe or ZnFe be OK?? Some say Fe
is electrically so bad that would not be much better than the ground I am
already having. So I am puzzled and please tell me if Fe is OK for radials
or not??(apart from the fact that it tends to rust)
2. I plan to add more elevated radials (4 per vertical) to find out if there
is any change in pattern, gain, F/B, bandwidth, etc.. AO shows me better
F/B and nicer pattern with 4 radials being symmetrical to the first one,
thus 4 radials crossing each other in the centre of the square. How close
can I put the elevated radials for them not to affect each other or spoil
pattern...etc? AO recommended about 20cm minimum spacing, is this justified?
Or do I just have to isulate them from each other???
For those who care to read more some more comments about the project:
I made the verticals exactly 20.5 meters long for the 3.65 Mhz and assumed
that I will do all fine tuning with the radials. So I also cut the radials
all initially 20.5m and connected the cables, the box and dummy load to
do initial measurements. I could not believe my eyes. The array looked as
if computer had fine tuned it, perfect!
I had SWR 1.0 from 3.4 to 3.9. Identical curves for all four directions.
And minimum dumped power into dummy load at 3.65 - 0 watts. At 3.8 Mhz i
had 10% of the power dissipated into dummy and at 3.5 Mhz about 15%. That
also almost identical in all directions. I think that I can easily live
with losing 10-15% of power on the edges and it is not worthwhile to retune
the radials for SSB and CW. That paves the way for me to install more elevated
radials.
I don't think there is any other advantage in having 1 elevated radial besides
the ability to tune easily. The high angle radiation one gets from such
a radial is really on 90 degrees and not useful at all! At the hight of
3 meters the horizontal component is quite negligible anyway. I would not
advise anybody to elevate the array more than by 3-4 meters as the pattern
gets distorted and you lose a lot of gain on very high angles. But it is
worthwhile elevating it 2-3 meters as your F/B improves a lot on high angles
and of course you lose less in the ground if you do not have perfect ground
screen.
So the first QSO was barerfoot with VK1MJ 58-58 and then it went on. Had
JAs answering my barefoot CQ and giving 59 reports and not audible reports
with other directions. The pattern seems great. At least 15 db F/B on local
signals and much more on DX signals. I guess my efforts trying to make
everything
accurate by millimeter paid off. I cut verticals, radials and feedlines
by mm and placed them on ground within 2-3 cm from the right spot, ground
is also even field so it all seems to pay off well although only one radial
is risky business of course as so much voltage is concentrated in one place.
I will install 4 elevated radials per vertical soon and AO gives me 5-10
db better F/B ratio in that case, especially on high angles and nice pattern.
I wonder if I see any change in bandwidth. I think more than 4 elevated
radials is waste of wire and effort provided you have a ground screen. But
having only 2 elevated radials spoils the pattern and could be worse than
only 1. 3 is almost as good as 4 but the most important thing is that they
have to be symmetrical. The more elevated the array is the more important
it is of course. I remember having seen somewhere W3LPL configuration with
2 elevated radials (all parallel to each other). Model shows that it is
is 5-10 Db down in F/B at 10 to 60 degrees from 4 elevated symmetric radials.
The W3LPL configuration is very similar to traditional ground mounted 4Square
patternwise.
I also feel that I am losing something on transmit to lossy ground (3-5db
maybe) as the 4SQ performs comparatively better on receive gainwise comparing
to Inverted V. It is very interesting comparing two antennas and as I can
easily model the patterns for both I can find out from what angles are the
signals coming in. I found that very local guys are often coming at 60-70
degrees even and DX below 20 of course usually, in the same time ZL came
at 25-30 degrees in my mind when it was his sunrise and my sunset (that
is not a surprise of course).
If anybody has any suggestions or comments I would appreciate a lot. it
is really fachinating to get such an antenna up and to test it and discover
so many new things.
73
Tonno
ES5TV
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