More on end-fed antennas

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.

The ideal end-fed, half-wave antenna. (from AA5TB.Com)

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:

Comments

  1. Elwood Downey says:

    I’ll put in a good word for the AA5TB site. I built a 40 m EFHW according to his information. Tuned using his procedures (basically resonate the tank circuit first with a resistor) I can confirm little or no counterpoise at all is required. Very convenient.

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