Wednesday, July 7, 2010

Windom antenna in an inverted-V configuration ...

Q Bob, VE3GND, asks, “I’m thinking about trying a Windom antenna in an inverted-V configuration. Are there any advantages to doing this?”

A There is only one antenna design that can be properly classified as a true Windom. The antenna was described in the September 1929 QST article written by Loren G. Windom, W8GZ, titled “Notes on Ethereal Adornments.” It was a Marconitype antenna, using a single-wire feeding into an off-center position of a long horizontal wire. With this design the whole antenna system radiated—there was no feed line used; the antenna was connected directly to the transmitter (see Figure 1). The resulting pattern is dependent upon the band of the transmission.

This antenna is not a good match to modern transmitters, but it worked quite well in its day, so a few modern antenna builders have capitalized on the famous name (much like the various “G5RV” antennas I have seen).

Commercial “Windoms” are generally not true Windom designs, but merely off-center fed (OCF) dipole antennas. Their chief advantage is that they resonate well on the frequencies that constitute a 1/4-wavelength for each leg of the antenna (or an odd multiple thereof).

The advantages to an inverted-V configuration of an OCF dipole are pretty much the same as making a standard dipole into an inverted V. That is, you get more radiation off the ends for a tradeoff of broadside radiation, and you can install the antenna with a single support.

On the other hand, when an antenna is used in the inverted-V configuration on higher frequencies than where the antenna is 1/2 wavelength long, the pattern degrades considerably compared to the pattern produced by a flattop under similar conditions.1

Figure 1—The true “Windom” antenna was described by W8GZ in his 1929 QST article.

From QST January 2000