Saturday, November 17, 2012

"Hang & Play" Classic Zepp Antenna

"Hang & Play" Classic Zepp Antenna

These days many Hams are seeking ways to improve their reception and up their signal strength, and are resorting to wire antennas from the past fed with ladder-line, used in conjunction with tuners and/or baluns to accomplish matching to 50-Ohm coaxial line. G5RV's and various flat-top configurations fed at the center, or off-center as in the Windom antenna, are very popular as well.
These are generally used as multi-band antennas, but usually require tuning of some sort on each band as previously mentioned. Routing the ladder-line into the operating environment sometimes results in RF voltage nodes appearing in the operating area (shack), and may cause interference/adverse affects to telephones, computers, and other electronic/ electrical devices used in the home.
When an end-fed antenna is desirable or when a center-fed antenna is not possible or convenient, Hang & Play™ end-fed Zepp antennas provide excellent no-compromise performance. The name "Zepp" harkens to the days of dirigibles, or Zeppelins, which used trailing wire antennas that, by definition, had to be fed at one end.
The MFJ version of the classic Zepp consisting of a ½ wave radiator certainly fits the bill in all these circumstances. And, as a bonus, you can virtually "hang & play" this antenna as we construct them. No tuning, trimming, etc. required. Once connected, you'll find the antenna presents a low SWR across the entire band. However, it is a "one-band antenna" depending on which band you chose.
Figure 1 is a generic illustration of the antenna with its shorted stub and coaxial connection.

Figure 1
Classic Zepp Antenna ("Hang & Play" Version)
Dimension "L" represents a ½ wave, and "F" represents a ¼ wave, which, in this case is a ¼ wave stub, used for matching and phase-shifting. The antenna is a "broadside radiator," bi-directional perpendicular to the run of the wire. A pair of these antennas at right angles (NE/SW; NW/SE for example) can provide world-wide coverage. And, when used with a suitable antenna switching system (Ameritron RCS-10), switching is convenient and fast, with only a single-line feed into the shack. Or, you can run both coaxial lines into the shack, and effect switching with a wall-mounted unit (MFJ-1700C).
If height is a constraint, this antenna functions better than average at even a bit less than a ½ wavelength above ground/structure. However, it really performs best if "hung" at a ½ wave; up to ¾ wave. Higher than that provides diminishing return.
Especially important is keeping the symmetry of the antenna in reference to its ½ wave radiator. It must not sag more than a foot or so, with pulled-tight being the best installation. The feedline/stub can be "bent" at the bottom, or pulled away at an angle, and some twisting is OK. Practically, it is best to let the stub/feeder hang straight down and tie it off with rope to avoid lashing about in windy conditions.
To summarize, these antennas are intended for single-band use (your favorite):
  • 17 meters (27 feet long; 13.5 feet high)
  • 20 meters (32 feet long; 16 feet high)
  • 30 meters (45 feet long; 22.5 feet high)
  • 40 meters (65 feet long; 32.5 feet high)
They require two tie-off points spaced far enough to accomodate their width/length, and a height at least close to ¼ wavelength. When using two antennas, try to locate the antennas in an "L" or "T" ("X") configuration (at right angles) as illustrated in Figure 2.

Figure 2
Two Antennas at Right Angles (Suggested Optimum)
We hope you will benefit from their ease of installation, efficiency, and quality construction.

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