Anténa End Fed Half Wave (EFHW) is light, low cost, multiband and therefore at first sight temptingly lucrative. To help understand the strengths and weaknesses of the EFHW antenna, I will try to present the construction in this article attributes, Properties, behavior, effectiveness and the resulting performance, which can be expected from an EFHW antenna. This could help many operators make informed decisions and also avoid various pitfalls, Many radio amateurs encounter this type of antenna, to later spend a lot of time and money trying to find solutions to various performance shortcomings.
The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency in all amateur radio bands provided, that it is properly powered. However, it has its peculiarities. The radiation pattern of this antenna in most bands creates several lobes. The orientation of these lobes varies with the frequency band of operation, leading to directional discrepancies between the bands. In addition, this antenna creates several interlocutal zero points, which create multiple shadows in its coverage (deaf) zone-dependent areas. Most EFHW antenna configurations resort to the use of wideband impedance transformers at the power point, to achieve acceptable SWR in all operating zones. This is usually a weak spot.
The overall arrangement of the impedance matching in this case is far from perfect, what leads to significant reactive currents in some bands. Parasitic reactances near the supply point also vary between installations. Therefore, there is no optimal simple solution. Each installation may require adjusting the antenna as well, to operate within acceptable standards… This condition is rarely met in a typical EFHW antenna field location, which leads to a reduction in the overall performance of the antenna system. The above factors often lead to an unacceptably high surface RF current (Common Mode Current) on the coaxial cable transmission line, leading to a relatively poor antenna system. The point is, that although the EFHW antenna has a promising potential, most amateur radio installations, which rely on the immediate use of a commercially available EFHW antenna, it can have many performance-related shortcomings. To make matters worse, many radio amateurs tend to believe, that this antenna could be positioned in any way, which they feel and yet will continue to work well… This is a misconception… Although acceptable SWR can be achieved in all bands, it does not necessarily mean that, that the antenna works well. Antenna radiation efficiency, lobe shapes, profit, etc., it all goes lost, if the EFHW antenna wire is placed randomly and at random orientations.
For example, standard and neat EFHW Inverted-V wire antenna configuration is much worse in performance than conventional horizontal configuration, not to mention other random orientations, which could often end up pretty bad. Read on, to understand the EFHW antenna, so you can learn, how to optimize EFHW antenna installation and avoid various performance pitfalls: https://vu2nsb.com/antenna/wire-antennas/multiband-efhw-antenna/
You can read more in the article VU2NSB about EFHW antenna
- For a good antenna system it is necessary to ensure, that the transmission line is in no way part of the antenna radiation system. It should be isolated from any possibility of playing a role in signal radiation. Comparison of EFHW antenna and dipole
- SWR is good, so i have a great antenna… Not? Not!!! … The low SWR you get means almost nothing, unless the various other antenna attributes are set correctly. Otherwise, it would not be perfect SWR 1:1 it didn't have to be good enough. Plus, a lot depends on it, which is the cause of low SWR. This is due to the good match of the antenna power point, or it is for ATU matching consistency?
- Typical characteristics and performance of EFHW antenna
- Impact on performance due to antenna placement in the environment
- The EFHW antenna is very practical and convenient for field use for temporary installations
- Optimum counterweight length and impedance transformer UnUn 8:1 (64:1 Z-ratio) are the best results to achieve SWR under 2:1 on all bands
- Influence of EFHW driver orientation on performance The best results are achieved with the classic placement in the shape of a horizontal wire. The Inverted-V variant should never have a top angle of less than 90 ° -100 ° when used. Preferably, it should be maintained at about 120 ° -130. More importantly, so that the endpoints of the inverted V are as high as possible, pre 80 m band minimum 4 m above the ground.
In the original article, for a better understanding of the topic, are animated pictures, charts and more detailed information. I wish you a pleasant and especially informative reading on this issue.
YOU 73! Fairy, OM3CAQ