It's Antenna Time
by Dan Romanchik, KB6NU
Here in Michigan, the daffodils are blooming and the birds are
singing. That means only one thing--it's antenna time! Since my lot is
a city lot and not really suited to towers, I mostly play around with
wire antennas. Currently, I have a random wire for 80m, a wire ground
plane for 20m, and a 40m/30m "fan dipole" that also loads up on 15m
and 10m. This year, I want to experiment with two new wire antennas--a
horizontal loop and Windom antenna.
The "Loop Skywire"
The concepts behind the full-wave loop antenna have been known for
many years, but the antenna has become more popular after the
publication of the article, "The Loop Skywire" in the November 1985
issue of QST. This article is available as a PDF from the ARRL
website, if you are a member
(http://www.arrl.org/members-only/tis/info/pdf/8511020.pdf). A lot
more information is available on Internet. Just Google "loop skywire,"
and you'll find hundreds of references.
Basically, the antenna is a full-wave loop of wire for the lowest
band that you wish to operate. For 80m, that would be about 272 feet.
For 40m, the length will be 136 feet.
Ideally, you'd like to set up the loop so that the area inside the
loop is at its maximum. This occurs when the loop is a circle.
Unfortunately, that's usually impractical. From a practical point of
view, most guys shoot for a square configuration using four supports.
Another consideration is how to feed the antenna. The Loop Skywire
article calls for a coax feedline, but the practice these days seems
to favor ladder line. The reason for this is that the SWR on bands
higher in frequency than the band for which the antenna was cut can be
quite high. Coax is quite lossy when the SWR is high, but that's not
the case with ladder line.
How does it perform? Well, it's been my experience that guys with
loop antennas often have the strongest signals here at KB6NU. And they
seem to get through even when band conditions are poor. Guys who use
them also report that they are great DX antennas as well. So, all
things considered, it sounds like it's worth a shot.
The Windom Antenna
The Windom antenna is an antenna that I've just become familiar with.
It's intriguing because, like the loop antenna, it is also a
The Windom is a half-wavelength antenna, but instead of feeding the
antenna in the middle as you would a dipole antenna, you feed it about
1/3 of the way from one of the ends. At this point, the feedpoint
impedance is about 200 ohms. With a 4:1 balun, you can feed it with
The interesting thing about this antenna is that the feedpoint
impedance is 200 ohms not only on the fundamental frequency, but it's
close to 200 ohms on all harmonics of that frequency. So an antenna
cut for 40m, will also have a feedpoint impedance close to 200 ohms on
20m, 15m, and 10m.
You do need a 4:1 balun for this antenna to operate properly.
Fortunately, these are not difficult to make. I made one a couple of
years ago, just for fun (http://kb6nu.com/even-more-fun-with-baluns/).
Now, I have an application for it!
There's all kinds of information on the Net about the Windom antenna
as well. One of the Web pages I found most useful was written by W8JI
I certainly have my hands full this antenna season. Whatever you
decide to put up, remember to be safe.
When Dan isn't thinking about antennas, he's operating CW on the HF
bands or teaching ham radio classes. He's just published a printed
version of his No-Nonsense Tech Class Study Guide. See his blog,
www.kb6nu.com, for more details.