I recently posted about end-fed antennas. That post basically criticized the seller of the “QSO King” antennas being sold on eBay. What he’s selling isn’t really what most hams think of when they think of an end-fed antenna.
What do most hams think about? For most hams, an end-fed antenna is and “end-fed, half-wave,” or EFHW, antenna. That is to say that the antenna is the same length as a half-wave dipole antenna. When the feedline is connected to the center of a half-wave antenna, the feedpoint impedance is theoretically 72 ohms, which is a good match to both 50-ohm and 70-ohm coax and the 50-ohm outputs of most ham transceivers.
When the feedline is connected to the end of a half-wave antenna, the situation is quite different. At the ends, the impedance is thousands of ohms. To connect a feedline there, you need some kind of matching device. This matching device transforms the impedance from 4,000 or 5,000 ohms down to 50 ohms.
If the impedance is so high, why would you want to use an end-fed, half-wave antenna? Well, for one thing, it’s sometimes easier to connect a feedline to the end of an antenna instead of the middle. It also makes the feedline much shorter.
With that in mind, here are some links to other resources on EFHW antennas:
- LnR Precision. LnR now sells the Par EndFedz line of antennas. These are hundreds, if not thousands, of these antennas out there, and I’ve never really heard anything bad about them.
- AA5TB.Com. AA5TB has a bunch of pages on the EFHW antenna, most notably articles on different couplers and an article on the basics of the EFHW antenna. He’s also posted a spreadsheet to help you design your own EFHW tuner.
- KC8AON’s 40 – 12 m EFHW Tuner. Most EFHW couplers are for a single band. This QRP coupler can be used with half-wave wires from 40 m through 12 m.