Some further experience with my 4 SQ in the woods (but using towers as the
radiating system). My system is elevated and sits on the slope of a hill. Set
the feed points at roughly the same height (highest feedpoint is 20 ft.)
I started with 8 radials per vertical and got reasonable results but when I
added another 8 for a total of 16, it made significant difference. The pattern
was more pronounced, F/B and F/S improved. Did not think adding more radials
would see the significant improvement I saw when going from 8 to 16 radials and
stopped adding more wire.
Moving soon to a new QTH where I plan to use wires hung from trees as verticals
and it will be over a wetland area. I will try the single radial approach
first to see how that works and eventually put in more radials (ground, in
water) later.
A similar system is possible on 160 M but this may come later. Regards, Mark,
K1RX
From: Tonno Vahk <tonno.vahk@gmail.com>
To: towertalk@contesting.com; cqtestk4xs@aol.com
Sent: Friday, September 23, 2016 5:43 AM
Subject: Re: [TowerTalk] 4 square for 80
Elevated radials work very well with 4 square elements if you leave the
ground loss question separate. I have 1 elevated radial per each vertical
(ca 6-8 feet high) for my full size 80m 4Square and in addition to that
passive ground screen of many radials under it to deal with the ground loss.
1 elevated radial has the huge bonus of being able to easily tune each
vertical by changing the length of the radial and not the vertical element.
The system works very well with DXE box and was mostly matching or beating
the 3 element yagi up 1/2wl (when it was still up before the tower crashed).
My soil is nothing special. Rather poor than good.
Secondly I have the very system of wire 4 Square for 160m built around a
rotating tower. The tower is 42m high and the wire verticals are hung from
the wires so that the upper ca 1/3 part runs along the wire diagonally up
towards the top of the tower. So in reality it is full size but with sort of
semi inverted L elements.
I have no ground screen and I have only ONE wire radial per each element off
about 7-8 feet from the ground. I have not detuned the tower in any way. And
it sill works OK. It has a poorer directivity and and less gain than the
full size 160m 4Square with 64 ground mounted radials per vertical. But it
works!
So Bill - I guess just hang up those wires, put 1 radial first, get it tuned
and see how it works! Does not cost much to try. You might be surprised.
I don't see the point of raising up 16 radials. Once you have so many you
can just put them on the ground unless there is a reason why you can't have
ground mounted radials.. Much easier to even put 64 on the ground than
raising 16 I guess. And then you get perfect result anyway.
73
Tonno
ES5TV
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Brown
Sent: Friday, September 23, 2016 6:37 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square for 80
Mike,
I don't always subscribe to "do what the mfr says" philosophy, but in this
case, you've gotten solid engineering advice. I'd say take it!
Engineering and science are NOT a matter of opinion, nor of popular vote.
Once you've gotten that good advice, say thank you and start building it!
One observation though about ALL vertical TRANSMITTING antennas. In general,
the PERFORMANCE of horizontal antennas is NOT affected by the quality of the
soil (although their feedpoint Z strongly depends on height and soil
quality), but the PERFORMANCE of vertical antennas is STRONGLY affected by
soil quality. I suggest that you study the antenna planning
tutorials/applications notes on my website. My QTH, in mountains where the
"soil" mostly rocks with a thick layer of "duff"
(droppings from redwoods laying on top) is quite poor, except during the
winter when our 70 inch annual rainfall makes that top layer fairly
conductive. So verticals don't work for me -- my only vertical antennas are
for 160M, where any practical horizontal antenna is too low to be good at
low angles. I've tried verticals on 80, 40, and 30M, and they had terrible
efficiency.
So -- take Tim's comparison of 4-squares for the higher bands with a Yagi at
50 ft with that in mind -- that is, compare his ground with yours.
Another important point about radials. Their function is to SHIELD the field
produced by the antenna from the lossy soil, so that return current for the
antenna flows in low resistance copper rather than lossy soil. BUT-- current
in radials couples inductively to the soil, so current flows in the soil,
burning TX power. The equivalent circuit of the radial adds a resistor in
series with it.
Power is I squared R; as more radials are added, the current divides between
them, while the R in each radial remains the same (if identically installed
and the soil is the same under each). SO -- as we double the number of
radials, we reduce the power in the radials by half. THAT'S why more radials
are better, and that's why 16-32 radials is the point of diminishing
returns. (Note that I'm not saying that the efficiency improves by 3 dB, but
that the loss in the soil is reduced by
3 dB).
As we RAISE our radials, there is less coupling with the earth, and it takes
fewer radials to keep the ground loss low. N6LF has done a LOT of excellent
work on this, and published it in QEX and on his website. It's well worth
the time to study it thoroughly.
When thinking about the effect of soil, there are two. First is the loss in
the radials, and we have control over that. We can put more copper in/on the
ground, or we can elevate radials. And we can use K2AV's FCP if we don't
have room for radials. The second effect is the loss in the far field where
the first reflection combines with the direct wave from the antenna to form
the vertical pattern. The strength of that reflection is strongly dependent
on the soil, and that is NOT under our control. THAT'S how sea water makes
verticals work so well, and ONLY in the direction where there's sea water.
73, Jim K9YC
On Thu,9/22/2016 2:12 PM, Tim Duffy wrote:
> Having engineered 4 square antenna systems (successfully) for over 25
> years
> - I was the advising engineer to Rod on your project. I was very
> careful to make sure Rod had all of his facts correct before giving you
advice.
>
> You asked for advice on your project and we gave you the straight
> engineered scoop - with tons of experience. We do not want you to go
> through lots of work only to find out a system you proposed does not
> work correctly. You might get various other guidance from others, my
advice is be careful.
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