M0AWS Amateur Radio Website

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14Mhz - 30Mhz Slot Fed Skeleton HF Antenna

I fumbled my way across this antenna whilst messing around with antenna designs, namely a 3 element yagi beam pointing upwards for NVIS propagation, I know it sounds daft but it’s true !
 
I thought I’d discovered a new type of antenna but after some searching on the web and various antenna books I have in the shack I discovered that this is actually a “Slot Fed Skeleton” Antenna for the HF bands (14.0Mhz – 30.0Mhz)
 
For such a simple antenna it has a remarkably low angle of radiation on the design frequencies and will fit into a typically small garden most HAMs have to operate from.
 
So, without further delay let’s get straight onto the design.
The antenna basically resembles a letter “H” with the top and bottom linked and then fed in the middle of the centre bar with 450/600 ohm open-line feeder.

The dimensions are as follows:
 
        Wires 1, 2 & 3            3m
        Wires 4 & 5                9.2m
 
Wire 2 is cut in the centre and the open line feeder (450/600 Ohm) is attached to each half of the element.
All wires are 2.5mm and are supported by wooden frames suspended from the top.
Since this is a balanced antenna it will need to be tuned using a suitable ATU/Balun arrangement.

The radiation patterns vary slightly, but once above 18Mhz the pattern is almost identical.

20M Band – 7.91dBi gain at 24 Deg
17M Band – 9.12dBi gain at 20 Deg
  
On the 15m, 12m and 10m bands the radiation angle changes quite drastically such that the antenna exhibits a deep, wide null in the centre and a high gain, low angle of radiation

15M Band – 9.65dBi gain at 16 Deg
12M Band – 10.16dBi gain at 14 Deg
10M Band – 10.98 dBi gain at 12Deg
 
(Figures calculated with TOP of antenna 15m above average ground)
See the antenna layout, radiation plots an SWR sweep below.