What is an End Fed Half Wave (EFHW)
It’s a multi-band antenna that is a half-wave on the lowest band of your choice. The simple calculation is 144 / f (MHZ)
3.6 MHz = 144/3.5 = 41.15m of wire
So we can construct a simple, handy table for construction
| Freq | Length |
| 3.6 MHz | 41.15 m |
| 7.1 MHz | 20.28 m |
| 14.2 MHz | 10.14 m |
| 21.3 MHz | 6.76 m |
| 28.5 MHz | 5.05 m |
In practice, you want to select the longest length from this tablet that you can get to work in your setup. If you are lucky enough to have 20+ meters in your garden, then selecting a wire length of 20.28m will give you access to 7, 14, 21 and 28 MHz.
Conversely, if you can only fit 10.14m of wire in your garden, then you will have access to 14, 21 and 28 MHz.
Transformer or matching required
You can’t simply cut the wire and connect it to your radio without impedance matching; your typical ATU will not be able to handle the 2,500 to 3,500 ohm impedance, and so we use a 49:1 or 64:1 impedance matching transformer (often called a balun or unun). In truth, it doesn’t matter whether 49:1 or 64:1 will achieve the results needed. We have to make something like 3,000 Ohms look more like 50 to make the radio happy.
50 x 49 = 2, 450 or 50 x 64 = 3200 (so they are both close to the range we spoke about) will both provide a reasonable impedance match to 50 Ohm.
This way you won’t need another ATU, you can simply coax feed the 49:1 and then add the wire length as discussed.
Do I need a counterpoise?
You can if you wish, have a small counterpoise, but you can also use the braid of the coax if you want. If you do use the coax, remember to add a 1:1 at some point to stop the coax from radiating back to the radio.
If the EFHW a magic antenna
No, it’s a compromise antenna on anything other than the band it was designed to work on, but it is a multi-band antenna and will work. Its worth remembering that multi-band antennas are convenient, but they can never work as well as a dipole or vertical (single-band antenna). Sure, you can use an EFHW as a vertical, and they will, no doubt, work well.
Mostly in amateur radio, we are looking for low-cost convenience. If you want the best antenna, then I would suggest a mono band HF beam with as many elements are your tower will support.
You can make or buy a 49:1 or 64:1 matching transformer online HERE
The matching transformers are usually quite small for 100 or 200w watts, they get much bigger and expensive for 400 to 1KW power ratings.
Points to remember
The EFHW antenna does not work well when you cannot get it in the clear. People often say, “It’s useless,” which typically means they can’t get it to work wrapped in a tree or running along the fence.
Don’t run high power on data modes. if the 49:1 is rated for 100w, then 40w FT8 is most likely the maximum power you should run.
The end can be high voltage, so make sure it’s safe from people or animals.
Its never going to be the best antenna in the world, but they are quick to set up and can be ideal for portable operations.