Q John, KU4KZ, asks, “I have a Yaesu FT-990 transceiver that I use with a Carolina Windom antenna. Most of the time I use my antenna tuner, but the other day the tuner was accidentally in the bypass mode. I noticed that the tuner’s SWR meter was moving as I talked. It seemed to kick up as high as 2:1. I was running about 100 W output. When I brought the antenna tuner into the line, the needle did not move when I transmitted. Can you explain this?”
AYes, I believe I can. To answer your question, let’s briefly
discuss what an antenna tuner and an SWR meter do.
Part of the function of an SWR meter is to measure any power that is reflected back to your transceiver that’s caused by an impedance mismatch in the antenna system. Most modern rigs are designed to accommodate antenna impedances of 50 Ω. If the impedance at the antenna system input is anything other than 50 Ω, power will be reflected back to the radio. The reflected power needle on your SWR meter will indicate this power. If it reads zero, there is no measurable reflected power.
The job of the antenna tuner is to match the antenna system impedance to that of the transceiver. Note that an antenna tuner doesn’t “tune” anything—it matches two dissimilar impedances. The antenna tuner transforms whatever impedance exists at the end of your coax to 50 Ω for the radio. When impedances are matched there is no reflected power and, again, the reflected power needle will read zero.
So, when your antenna tuner was bypassed you were seeing
the result of having your transceiver connected directly to the
antenna system. The SWR meter indicated that reflected power was present as you spoke. (In SSB, power is generated only when you actually speak.) When you switched your tuner back in, the impedance mismatch was transformed to 50 Ω and the reflected power at the SWR meter dropped to zero.
By the way, don’t worry too much about harming your FT-990 this way. Like most transceivers, the FT-990 includes a foldback circuit that senses when there is too much reflected power getting into the radio. The foldback automatically reduces the output to a safe level.
From QST July 2000
Showing posts with label Windom antenna. Show all posts
Showing posts with label Windom antenna. Show all posts
Friday, July 23, 2010
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
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
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