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A touch of Class, and A touch of the Past the J-POLE
By Glynn E. "Buck" Rogers Sr (K4ABT for 60 years)
Between the articles by the lateLew McCoy W1ICP and myself,
the J-POLE, Windom, and ZEPP should be around "forever."The J-POLE has been around since the early days of HAM Radio, and is a direct descendant of the "ZEPP." Like the ZEPP, the J-POLE is a spin-off, or a modified WINDOM for VHF. One of the first articles I wrote about the J-Pole was in HRC magazine in 1958. Since 1958, I've written several j-pole articles in other HAM Radio publications.Here, my references are to the early, 1923 (version) Windom (Article by Loren G. Windom September 1929, QST magazine) . If you look at the off-center feed of the early Windom that was fed with a single wire, you can soon see the similarity between the Windom, ZEPP, and the J-Pole.For now, let's look at some of the features of our J-Pole, whether for; 50-55 MHz, 140-150 MHz, or 430-450 MHz.
The J-Pole father, the "Windom Antenna" was described by Loren G. Windom in QST magazine, September 1929. Pages 19 through 22.
Loren Windom, W8GZ, was first to reveal the antenna to the radio amateur community by describing the antenna in the September 1929 issue of QST. It was by Windom's name that the antenna became known. The Windom antenna is an off-center fed dipole with an unbalanced coax feedline.
In 1937, the Windom was first described as a compromise multiband antenna. The antenna can be employed on 160, 80, 40, 20 and 10m with considerable, though acceptable levels of VSWR. What became perhaps the most popular multiband Windom design of all, was the German-made Fritzel FD4 antenna, described by the late Dr. Fritz Spillner1, DJ2KY, in 1971. It had the same dimensions as the multiband Windom antenna, but fitted with a 200Ω (4:1) balun at its feedpoint and fed with coax.
Today, many radio amateurs are using multiband Windom antennas with more than satisfactory results. It would not be without reason that Windom antennas are being employed during IARU HF World Championships! and most of all, by "high-stake-contests." Perhaps many young hams ignore the multiband Windom antenna because of its sheer simplicity and may be thinking it is too good to be true. The complexity of feeding other dipoles and doublets, the losses in dipoles with traps and the esoteric marketing of some other antennas seem to appeal to them more.I've had many requests for a ready-made J-pole design that will enable the Packet Radio user to print the image from a web page and go directly to the construction table and build a J-Pole antenna for their HAM Radio station. The object is to eliminate the need to go through all the calculations on another page of this website. These requests are valid and understood! With your requests in mind, here are "the real world" designs that I've personally constructed and use at many of my Packet Radio node locations. To make a hardcopy of this web page, go to the small "printer" icon of your Internet Exployer (or NetScape) browser and CLICK on the printer icon. This will enable you to print this text and the attached illustrations for future use. A VARIATION ON A THEME: Let's look first at FIGURE 1a; This is the overview and profile of the J-Pole we will be working with. There are two different bands we will be building the J-Pole antennas for. NO, we will not build a two band antenna on one mast. I've been there, done that.. and it is an excercise in futility. For openers, I would like to show you that all J-poles are not created equal. By that statement; I mean, we will modify our construction techniques a bit and apply a variation to the theme. Notice in the exploded view at FIGURE 1b, I've deviated from the usual RF feed technique that we normally use to attach our coaxial cable to the J-pole. Where we usually attach the shield and center conductor to the tuning stub and the driven element with aeroseal (hose) clamps, here we've made a slight change in the design by exchanging the elbow for a tee. Below the short (1/4 wave tuning stub) section, we (carefully) soldered an SO-239 (Chassi-mount) coax (female) connector. But notice that we must first attach a piece of number 10 or 12 insulated, copper wire to the SO-239. The length of this wire depends on the spacing between the stub and (Fig 1A "D") long section of our antenna. If the antenna is for six meters, the wire length will need to be about, 10 to 12 inches long. If our antenna is for two meters, the wire length will be less than 8 inches overall. I am careful when I (Benz-O-Matic torch) solder the SO-239 to the copper tee, since I don't want to heat the SO-239 to the point the solder on the wire melts and I have to start the process over again.For 2 meters (145.000 to 146.000 MHz) the EXACT dimensions are: A = 58 inches overall (Long, driven element). B = 19.5 Inches C = 2 Inches D = 1.8 Inches (space) For 6 meters (50.500 to 51.500 MHz) the EXACT dimensions are: A = 166-3/4 inches overall (long, driven element). B = 58-3/4 inches (short, tuning stub). C = 5.5 Inches D = 5 inches
FIGURE 1a
Figure 1bUSE BUX "VBALUN" withJ-Poles 1 kw VHF Balun, BUX VBALUN $19.95
Hi-Q, toroid design, wound with teflon covered, silver wire. For VHF beams and J-Pole matching applications, and construction.
An adjustable VSWR, 2 meter J-Pole 
BUX VBALUN should be installed at the antenna feed point, or where the coax or feed-line attaches to the J-Pole antenna. BUX BALUNs are used to connect balanced antennas to unbalanced transmission lines, such as coax cable. Their primary purpose is to prevent antenna (RF) currents from flowing down the outside of the cable. Another function of the BUX BALUN41 is to match the impedance of an unbalanced coax to the balanced feed point of a balanced input antenna(s). BUX BALUNS may also be used as �line isolators� anywhere along the cable to prevent the destructive influence of induced RF currents (VSWR). BUX 1:1 BALUNs are current BALUNs. They consist of several large, number 73, ferrite type 44 cores.
CLOSE UP of the alternative coax feed method.
Use BUX VBALUN to couple coaxial cable to J-Pole.
My Hardware J-Poles from 1969
BUX COMM, 142 to 150 MHz; Fiberglass J pol
For low terrestrial noise, use fiberglass elements. For optimum performance and gain,
feed with BUX COMM "VBALUN."
Courtesy HRC Antenna Newsletter (c)
BUX COMM, 435 to 450 MHz; Fiberglass J pol
For low terrestrial noise, use fiberglass elements. For optimum performance and gain,
feed with BUX COMM "VBALUN."
Courtesy HRC Antenna Newsletter (c)
The "VBALUN" is similar to our BUXUNUN, except constructed for VHF and UHF frequencies.
Primary use and application:
Feed point isolation and matching for J-Poles and VHF/UHF BEAMS.This decoupling transformer prevents RF currents from traveling down the outer shield of the coax. The input connector is an SO239 (female) and the output connector is a PL259 (male).
BUX "VBALUN" De-Coupling transformer, has SO-239 (female) input connector. Output connector is 2 feet RG8X cable with Amphenol PL-259 (male). BUX VBALUN is an UNbalanced to UNbalance decoupling transformer designed to be used by the Apartment dweller or the RV ops when feeding J-Poles and similar VHF/UHF antennas.
$19.95 VBALUN
Teflon �� E I DuPont corp.
Amphenol �� TYCO Corp.
BUX VBALUN should be installed at the antenna feed point, or where the coax or feed-line attaches to the J-Pol connector
Important Notice; WHY USE A 4:1 BALUN
Krusty Olde Kurt is now going to repeat himself. Why? Because the same question keeps coming up over and over. And he wants everyone to get it right.
"I'm feeding my dipole with 600-ohm line. At the station end I need a balun to convert to 50-ohm coax. I need a 12:1 balun, right?" Wrong! A 4:1 balun would be better.
Why is that? If your dipole is up, let's say, 35 feet then on 80 meters it will probably have a resistance at resonance of about 40 ohms. The actual resistance depends on the height above ground in wavelengths.
If the dipole is 40 Ohms then what do you see at the transmitter end of your 600 ohm line? If the line is a half-wave long (120 ft on 80 Meters) you'll see 40 ohms. Remember, a half-wave line repeats what it sees at the other end. But if it is a quarter-wave long you'll see 8500 Ohms! At other line lengths you'll see impedances somewhere between these two extremes.
So you are not going to see 450 ohms at the end of your 450-ohm line. That only happens if you have a 500-ohm antenna hooked onto it. With such a variation in impedance at the trans�mitter end of the line there is no one balun transformer that will match it. Most of the time the impedance will be above the 50 Ohms of your coax so a high impedance balun would be desirable. Unfortunately high imped�ance baluns don't work well when not matched.
Experience has shown that 4:1 baluns work best in this service. They are more rugged and will take bad mismatches especially if they are wound on an iron powder core. So stop searching for that 9:1 or 12:1 balun. Use a 4:l BALUN and your system will work great.
You can read Kurt N. Sterba �AERIALS� column in World Radio Magazine.
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