Saturday, 14 May 2011

What happens to the performance when a HF dipole installation is raised?

I was sort-of satisfied with my folded dipole for 17m and 20m bands, when it was up about 10 meters. Still I wanted to optimize it...I am a radio amateur, right? After a couple of hours of sweaty climbing and wire tinkering I found myself looking at a dipole that is horizontally at almost 20 meters up, the wires pointing roughly to north-west and south-east. I don't know, if that's a good direction...I don't need directivity gains especially, since I work all the world and at random times, but let's try the antenna now! Well, I need a shower first...

The folded dipole for 14MHz and 18MHz is now almost 20m up. (Click for bigger picture)
Zoomed picture of the dipole up in the sky. The spacing between the lines is 30cm (not cricital) and  the  RG-58 cable  connects to  a 4:1 balun.
The VOACAP propagation forecasting tool showed interesting changes in the antenna performance:
A sample VOACAP propagation forecast for 11.May 2011 16 UTC for a 14,1 MHz QSO where my the dipole at the other end is 10 m up and my dipole is 10m up.

...and here is how the forecast is affected by moving the dipole to a height of 20m.
And what is the real life?
It was late afternoon, when I swithed on the radio, eagerly waiting for the results. I know from theory, that this height is really good for 17m and 20m little concern was: do I get DX QSOs on east and west directions with this installation?

When I sat down in my shack I decided to start calling CQ with PSK125 on 14 MHz. BD1MWH from China responded at once...not bad! Soon I had PSK and RTTY QSOs with ham fellows in South Korea, Philippines, South Africa...and later in the evening also Brazil and Bolivia on CW. Three new DXCC countries in the same day!

How is this with Eznec?
Elevation diagram for my horizontal dipole.
The lower lobe is at an angle of 13 degrees and the higher is at 45 degrees
The azimuth diagram for the 13 degree lobe. Good DX possibilities in two directions.

The azimuth diagram for the 45 degree lobe. Directivity is not that much of an issue,
which together with the high elevation angle enables good QSOs in Europe.


  1. Can you give me total length your antenna ??
    tnx 73 de yc2lev

  2. I don't remember the exact final length :) I made it like this:
    1. I calculated it for 14.050 MHz: (300/14,05)*0,95= 20,28m.
    2. I cut at about 21m, folded it, measured initially an SWR at almost 3:1. Cut it little by little until 1,5:1 was achieved.
    3. When I rised the antenna up in the tree, the SWR was again about 3:1.

    Well...even if I knew this will happen, I was surprised :) since his was my first homemade antenna. The resulting antenna was a litle bit too short to be optimal for 20m. But, since a folded dipole is broadbanded the antenna now works really well for 20m ant 17m. I use an antenna tuner for finetuning the impedance...I'm not sure whether that is necessary.

  3. In a chat in we checked: a ham was 900km from me in a the weakest direction from my antenna: we barely heard eace other...this obviously means that my antenna is installed high enough :)

  4. I added Eznec diagrams to this blog text 13.June 2011.

  5. I just wrote a theoretical comparison to a vertical dipole: