Besides location, the take-off angle is most likely: the most important topic for anyone who wants to work DX (or shoot skip hi).
Though perhaps some DXers migth not be aware of how important it actually is.
On this site we have often referred to the different take-off angles from different types of antennas and their heights, why is that so important ?
We can learn that through propagation via the F2 layer the maximum distance reachable in a single hop is around the 2500 km (many information about propagation is available on Internet or better by reading books).
We can not change anything in our favor about that F2 layer, we will just have to wait till for a good sun burst so it reflects to is abbility.
But we can aim our signal towards that layer at the lowest possible angle. In that way we obtain our maximum distance….and we will hear and work that remote Island.
Similair like a bouncing small rock across the water…. low angle in… lots of hops. and best distance !
Above we see a some simple drawings of the earth and a layer from the ionosphere, in this case the F2 this was is one we used for DXing most of the time. That layer was situated about 200 to 250 km above the earth.
Taking a closer look at the second drawing we see the transmitted wave from the earth.
That wave starts at your antenna location.
Your radiated signal from the antenna is drawn as a red line.
The angle between the earth and the angle of your radiated signal is called the take-off angle. (T)
What it does is explained in the above drawings.
Where “A” shows a high take-off angle
(which is the case for a horizontal yagi only a few meters above the earth.)
And “B” the take-off angle is low. (this one is produced by a very high placed yagi.)
That is in short what heigth can do for you….
WHAT CAN INFLUENCE THAT TAKE-OFF ANGLE?
To this question there are only three answers:
-
The polarisation of the antenna we use
-
The ground conditions around the antenna.
-
And the heigth of the antenna above that ground.
POLARIZATION OF A ANTENNA
First of all, one has to understand, from a “DXING” point of view it isnt important if you are vertical or horizontal or what the other end is using for polarisation.
This is because as soon as our signal hits the layers they are broken up in two parts (ordinary and extra-ordinairy) and they will start to rotate due to magnetic fields. They rotate so fast you cant manually switch or anything like that. If this is interesting, there are some good articles: google faraday rotation / propagation / hf.
So if all was the same, same gain…same angle …vertical and horizontal will produce equal results, regardless of what the other station is using.
But they are not the same they have different characteristics.
A vertical placed antenna produces a rahter low take-off angle while it can be “sitting on the ground”.
For example: a normal GPA is able to produce angle’s in the order of 18..20 degrees when it is fixed at ground level. This is something a horizontal antenna can not do.
In the plot below we can see a endfed halve wave with different heights 0,2,4,6,8,10 meters (keep in mind the TOP of the antenna is always 5..6 meters higher !
The plot is made above “average ground”.
We can see the vertical has a low take-off angle from start, the antenna also profits from heigth …there is some additional ground gain up to about 1dB when its placed at 12 meters.
The antenna actually has “negative” gain near ground. (0,4..06dBI ) where in freespace a “dipole” is known to have 2,14dBI
A horizontal placed dipole has to be at 5 meters above ground to do the same thing.
Below you can see the cross-over point, keep in mind… the horizontal diple is placed at 5 meters. The vertical bottom is at 1 meter (average ground conditions). You can allready notice the ‘hugh” advantage of “ground gain” for the horizontal antenna.
For that reason :
A horizontal dipole (or any horizontal antenna) placed lower then 5 meters will have probably worse DX results then the vertical. (providing gain is equal).
(Also keep in mind, that vertical placed at 12 meters will still outperform the horizontal at 5 meters for low angles.)
Just look at the larger HAM contesting stations and what they use for low band dxing..
A lot of verticals, simply cause mechanical it isnt possible to the horizontal antenna high enough.
One bad aspect of verticals is its ground, a vertical above bad ground (desert) can’t reach the high expectations which we just gave it. Horizontal antennas often outperform verticals under these conditions. Verticals bennefit from good ground and need an intens radial system.
Above good ground verticals perform outstanding, this effect seems to be amplified just think of those /MM stations..always strong signals from a salty sea.
You will have to deal with some other negative aspects of the Vertical antenna:
It produces more noises…so the station you want to hear is often deeper away
A vertical is more sensitive to QRM at the neighbors… etc
So when you can not place your favorite antenna high enough a vertical can be a solution for you if you want to work some DX.
Above 8 to 9 meters a horizontal antenna will produce a lower or the same take-off angel, thus better for “real” DX.
This antenna is from Paolo 1DX101,
The 3 elements Delta Loop has a boomlenght of 5,4 meters.
GROUND
Paolo is located on a little island in Italy
He is situated only 20 meters from the sea on the East front. 25 meters to the North and about 3 km from the Sea to the west. So….sea all around.
The antenna has a maximum height of 11 meters. With this station he reaches results everyone can be jealous off. Just take a look at cluster.dk and wait until he is on!
Paolo started in begin 2004 and is now (medio 2006) already on 189 confirmed DXCC’s
This is a great Example of what a great location could bring you with a great antenna!
And we all know that “one guy” who always hears and works everything..
His “location” migth just be the key for that.
So what is good ground ?
Just like the waves were refelcted in the sky, they are also reflected on earth. In order to be reflected…the ground must have a good conductivity (σ) and relative permittivity or dielectric constant (Er)
Our own “antenna pattern” depends on those two..it depends on the ground around the antenna. That pattern is “made” with influence of that ground. Roughly one could say…upto about 200 meter from your antenna is the “region of intrest” for your antenna.
The quality of that ground, how “good” it can reflect is named Ground conductivity and is expressed in millisiemens per meter (mS/m). together with the permittivity. (Er)
Obviously living in an industrial enviroment wont be as good as living remote near the sea with thick clay.
From 4NEC2 (1) we obtain the following average values:
GN card / Soil description |
Conductivity (S/m) |
Permitivity (diel-const) |
Relative quality |
Saltwater |
5 |
81 |
|
Fresh water |
0.001 |
80 |
|
Pastoral, low hills, rich soil, typical from Dallas, TX, to Lincoln, NE |
0.0303 |
20 |
Very Good |
Dallas, TX, to Lincoln, NE Pastoral, low hills, rich soil, typical of OH and IL |
0.01 |
14 |
Good |
Flat country, marshy, densely wooded, typical of LA near the Mississippi River |
0.0075 |
12 |
|
Pastoral, medium hills, and forest, typical of MD, PA, NY (ex of mountains and coastline) |
0.006 |
13 |
Average |
Pastoral, medium hills, and forest, heavy clay soils, typical of central VA |
0.005 |
13 |
|
Rocky soil, steep hills, typically mountainous |
0.002 |
12-14 |
Poor |
Sandy, dry, flat, coastal |
0.002 |
10 |
|
Cities, industrial areas |
0.001 |
5 |
Very Poor |
Cities, heavy industrial areas, high buildings |
0.001 |
3 |
Extremely Poor |
For verticals the effect can be seen below:
A comparisment with a vertical dipole placed 1 meter above ground. The plot show the (>3dB) difference between very poor ground and very good ground.
For horizontal antenna, with heigth the effects of ground become less.
Below an example of a 5element placed a 5,5 meters high above heavy city ground compared to very good ground: The gain improves from 12,0 dBi (heavy city) up to 13,43 dBI. There is 1,43dBI gain difference.
Below you will find a 5el placed 11 meter high in extremely poor conditions and in very good conditions:
The gain improves from 13,98dBI (heavy city up to very good ground :14,97 dBI). There is 1dB gain difference.
Below an example of a 5element placed a 20 meters high above heavy city ground compared to very good ground: The gain improves from 14,69 dBi (heavy city) up to 15,31 dBI. There is 0,62 dBI gain difference.
So simply by adding heigth to the antenna the influence of bad ground becomes less
It went from 1,43dBi to 0,62dBi.
It is actually not that difficult to measure the conductivity, but that is for another chapter.
There are online maps availible to see in your area how “good” the ground conductivity is.
https://hamwaves.com/ground/en/
Keep in mind this is “raw” data…living in the city will have a negative influence compared to “just out of town”.
(1) 4NEC2 a antenna modeling software by Arie Voors
DX LOCATIONS
For maximum use of the normal space wave it is important to have the antenna as high as possible above nearby buildings, trees, wires and surrounding terrain. A hill that rises above the rest of the country is good locationfor a station of any kind. The highest point is not necessarily the best location for the antenna. In the drawing above the hilltop would be a good site all directions but if maximum to the right is the objective, a point just below the crest might be better.This would reduce the coverage in opposite direction. An antenna situated on the left side, lower down the hill, might do well to the left, but almost certainly would be inferior in performance to the right.
Selecting a good DX spot (portable or home QTH) is not easy and depends also on which band will be operated. For our band a wide saltwater horizon, especially from a high cliff, just smells of DX.
(Source ARRL antenna book)
THE HEIGHT VERSUS TAKE-OFF ANGLE.
As said and not for nothing, height is important.
If you are searching for a big signal on the other side of the world there is are two solutions :
bigger and higher!
Above looking at the GIF we can see a 5elements yagi above average ground and its take-off angles at different heights. (4-26 Meters).
That angle is true for ALL horizontal yagi antennas.
They will all have the same take-off angle at the described height.
It is of NO interest if that beam has 3 or 10 elements, the angle remains the same.
One can clearly notice the advantege of heigth for receiving those low angle DX !
The table below is thus for ALL horizontal placed antenna above average ground.
They will have the following take off angle’s (T/A) at named heights.

A rough formule which was can be used in the field to get a approximent idea =
14xlambda/heigth. = elevantion angle in degrees.
(formula credits : PA3DJS)
Example: 14×11/20 = 7,7
14= 14, 11=lambda, 20=height …outcome is 7,7 degrees angle.
The table above shows where the main signal is radiated ( we still have radiation at other take-off angles as well.)
Do not forget there is a big difference between take-off angle and gain.
If you compare these with the different take-off angles provided in the chapter verticals, you can see when a horizontal antenna (with the same gain) will outperform the vertical.
For example if you are NOT able to erect a yagi in the near of 8..9 meters, say when you are on a DX-expedition you just might be better of with a vertical
(in both cases the antennas nearly the same gain.)
A grafical impression of take-off angle versus heigth and gain:

NOT ALWAYS?
Which angle are you looking for?
Well to give you an impression: Pacific for Europe 1-5 degrees. Those are the lower ones and for Europe these angles should be around the 25 degrees.
With programs like VOACAP or with YTAD and The program Yagi Terrain Analyzer from K6STI Which comes with the ARRL-Antenna book.
You can calculate what angle you want for a certain DXCC!.
With this knowledge you can understand that in some cases it can be better to place a high small yagi say a “cheap” 3 elements yagi instead of a lower big gun 5 elements long john. It just depends what you want: are you truly searching for that opening into the pacific for that last DXCC you just might put your money into a higher mast.
Below you can find the plot of a 5,5 meter boom average 5elements yagi (in blue)
With about 9,5dBI freespace gain when situated at 10 meters above ground.
Included is an average 3elements yagi (in black)
With only 2,7 meter boom situated at 18 meters above ground.
It is clear the 3elements yagi will be the winner for that long haul DX !
Height is might !
The conclusion Which can be made is: for DXing it might be wiser to spent money in height then in boomlenght.
What about a bigger antenna then?
If you are limited in height then YES go for a bigger yagi a change from a 3 to a 5 elements is definitely a big improvement!