The end-fed half wave (EFHW) antenna is a great choice for POTA operators wanting more than one or two bands because you get four, all without needing a tuner. My EFHW antenna is resonant on 40m-20m-15m-10m using a simple 65.3-foot piece of wire. A tuner is typically not required.
Theory:
While the impedance of a center-fed half wave dipole is approximately 73 ohms, the impedance of an end-fed half wave wire is much higher, like 2,000 ohms or more. A 49:1 transformer can be used to match the EFHW to your 50 ohm coax and transmitter.
While you could buy a ferrite toroid and wind your own transformer, by the time you add a SO-239 or BNC antenna connector and a suitable housing it might cost less to buy a ready-to-use unun like one I found on Amazon for < $30.
Goozeezoo 49:1 Unun
You can pay an extra $51 for a ready to deploy antenna with unun, wire element, insulator, and hoisting rope. Instead, I added my own wire and paracord for an inexpensive POTA antenna.
EFHW Antenna
EFHW SWR
showing dips < 2:1 at 40m-20m-15m
(there is another dip at 10m not shown)
WARNING: The transformer significantly raises the voltage at the antenna terminal. A transmitter delivering 100 watts to a typical EFHW antenna will see about 500 volts (700 volts peak) at the output of the matching transformer. Keep the unun away from potential contact by people. This is why I suggest a configuration with the feedpoint (and far end) elevated well beyond reach.
reference: www.n6cc.com/end-fed-half-wave-wire-antennas/
Details of my 40m/20m/15m/10m EFHW Sloper:
• element = 65 feet 4 inches of 18 gauge insulated wire
• approximate height of feedpoint: 40 feet
• paracord extender = 15 feet
EFHW Sloper
Other configurations are possible e.g. horizontal, sloping up (vs down), inverted-V, and inverted-L. I recommend keeping the unun as high as possible and well out of reach because there can be dangerous high voltage at this end of the antenna.
It is very important to note that the coax feedline is also part of the antenna and acts as a counterpoise. Moving or reconfiguring how and where the coax lays on the ground can affect the SWR and performance of this antenna. Experiment!
TIP: If you don't have room for a 40m half wave wire, you can still use the same unun with a 33-foot element and get both 20m and 10m.
TIP: Instead of a ring terminal, use a push-on "disconnect" terminal on your wire element and install a quick connect tab on the unun. This way you can easily change out the wire for a different length in the field.
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Push-On Connector on Wire |
Quick Connect Tab on Unun |
TIP: To add 17m and 30m check out my new Linked End-Fed Half-Wave Sloper! |
