The 10-meter "Hentenna" loop

 

This clever little antenna developed by JElDEU of Sagamihara City, Japan. Local hams were amused by the loop; hence the name - "hen" means curious in Japanese. "Henantenna" was quickly shortened to "Hentenna." It's shown in Figure 1. This antenna's virtue is that it has very little "wingspread"

The array has two one-sixth wave radiators separated vertically by a half wavelength. To feed them, connect the tips and tap the vertical wires with a coax feedline. Polarization is horizontal. Hentenna construction is simple. You use a single mast; try a TV-style pushup one. Make your horizontal sections out of 518-inch diameter aluminum tubing bolted to a mounting plate, and attach the plate to the mast with Ubolts. Use enamel-coated copper wire for the antenna's vertical sections. Feed the Hentenna with a balun and coax line. Run your feed wires from the balun to the vertical wires. Adjust for lowest SWR by moving the feed wires up or down the vertical wires. Copper alligator clips are ideal for this; you can remove them and make joint solders when you find the correct points. The points should be about 36 inches above the bottom tube for 10 meters. The Hentenna provides a figure eight pattern at right angles to the antenna plane. Gain is estimated at about 2.5 dB over a dipole. Bandwidth is very broad. By changing the length of the vertical wires, you can move the design frequency to any point in the 10-meter band.

Receiving loop antenna for 160 meters

 

Height of loop above ground is 10 feet. Illustration A is view from above. Illustration B shows 4:l balun and antenna tuner.

One of the problems in working DX on 160 meters is the high level of background noise. Many DXers have found that they cannot use their transmitting antenna for reception - the noise level is overpowering. Paul McClure, KDBSO, met this problem head on and evolved a horizontal receiving loop that provides good signal-to noise ratio. The loop's signal pickup isn't as good as that of a larger antenna, but noise drops off sharply. By adjusting audio gain of the receiver, you can bring the resulting signal up to the original level. Paul says that, out of the noise, he can pull weak signals that didn't seem to exist under normal circumstances. He says the antenna is comparable to a good Beverage wire. The loop, however, takes up less space and there are no terminating resistors to replace after a thunderstorm. The above-ground height of the loop is about 10 feet. It's fed with a random length of 300-ohm ribbon line. Paul twists the line to balance it to ground.

The bi-square array for 18 MHz

 

The diamond-shaped bi-square beam is much larger than the delta loop, but provides about 3-dB gain. This is a great antenna to try if you have the space. It's shown in fig. The loop is a half wavelength on a side and open at the top. The feedpoint impedance at the bottom of the loop is about 2900 ohms; I use a twowire 600-ohm quarter-wave stub to provide a more reasonable impedance value of about 122 ohms. Match it to a 50-ohm coax line by adding a quarter-wave transformer made of 75- ohm coax. Wind the 75-ohm line into a coil about 6 inches in diameter to reduce RF currents flowing on the out-side of the coax. Resonate the loop and stub to 18.1 MHz with a dip meter. Temporarily close the stub at the bottom using a movable short with a I-turn loop in the middle.

"Quickie" antennas for 18 MHz

 

The delta loop in fig. 1 is a good 18 MHz "first" antenna, It has slight gain over di-pole and user friendly

The feedpoint impedance of the loop is about 120 ohms .Use a 75-ohm quarter-wave transformer to provide a reasonable match to a 50-ohm coax line. The transformer is wound into a coil to choke off RF currents that might flow on the outside of the coax shield.

The feedpoint of the loop terminates in an SO-239 coax connector mounted on a small insulator plate. The transformer has PL-259 plugs on both ends. Make the splice between the transformer and the 50-ohm line with a PL- 258 splice adapter. After making the connection, weatherproof the plugs and adapter with coax tape or heat shrink tubing. The loop is supported at the apex and the side insulators are tied off to objects nearby. The radiation pattern is similar to that of a dipole and is horizontally polarized.

The 1.8-MHz inverted L.

 

Overall wire length is 165 to 175 ft. The variable capacitor has a maximum capacitance of 500 to 800 pF.

The antenna shown in Fig is simple and easy to construct. It is a good antenna for the beginner or the experienced1.8 MHz DXer. Because the overall electrical length is greater than 1/4 ë, the feedpoint resistance is on the order of 50 Ù, with an inductive reactance. That reactance is canceled by a series capacitor, which for power levels up to the legal limit can be a air-variable capacitor with a voltage rating of 1500 V. Adjust antenna length and variable capacitor for lowest SWR. A yardarm or a length of line attached to a tower can be used to support the vertical section of the antenna. (Keep the inverted L as far from the tower as is practical. Certain combinations of tower height and Yagi top loading can interact severely with the Inverted-L antenna—a 70-ft tower and a 5-element Yagi, for example.) For best results the vertical section should be as long as possible. A good ground system is necessary for good results.

Portable 3 element 2M beam antenna

 

In April 1993 QST, Nathan Loucks, WB0CMT, described the 2-m beam shown in Fig. The boom and mast are made from 3/4-inch PVC plumber’s pipe. The three pieces of PVC pipe are held together with a PVC T joint and secured by screws. Elements can be made from brass brazing or hobby rods. (If you can’t find a 40-inch rod for the reflector, you can solder wire extensions to obtain the full length.)

Drill holes that provide a snug fit to the elements approximately 1/4 inch or so from the boom ends. Epoxy the director and reflector in place after entering them in these holes. A pair of holes spaced 1/4 inch and centered 16 inches from the reflector hold the two-piece driven element. The short ends of

the element halves should extend about 1/4 inch through the boom. Solder the 50-Ù feed line to the driven element as shown in Fig

Loucks used a pair of 4-inch pieces held in place by #12 or #14 jam screws (electrical connectors) toextend and adjust the driven element to allow for operation in various parts of the 2-m band. You can trim the driven element to length for operation in the desired portion of the band if you prefer. The figures show the beam assembled for vertical polarization. You may want to turn the boom pieces 90° for horizontal polarization for SSB or CW operation.

10-m rectangular loop antenna.

 

With the large number of operators and wide availability of inexpensive, single-band radios, the 10-m band could well become the hangout for local ragchewers that it was before the advent of 2-m FM, even at a low point in the solar cycle.

This simple antenna provides gain over a dipole or inverted V. It is a resonant loop with a particular shape. It provides 2.1dB gain over a dipole at low radiation angles when mounted well above ground. The antenna is simple to feed— no matching network is necessary. When fed with 50-Ù coax, the SWR is close to 1:1 at the design frequency, and is less than 2:1 from 28.0-28.8 MHz for an antenna resonant at 28.4 MHz.

The antenna is made from #12 AWG wire (see Fig ) and is fed at the center of the bottom wire. Coil the coax into a few turns near the feedpoint to provide a simple balun. A coil diameter of about a foot will work fine. You can support the antenna on a mast with spreaders made of bamboo, fiberglass,

wood, PVC or other nonconducting material. You can also use aluminum tubing both for support and conductors, but you’ll have to readjust the antenna dimensions for resonance. This rectangular loop has two advantages over a resonant square loop. First, a square loop has just 1.1 dB gain over a

dipole. This is a power increase of only 29%. Second, the input impedance of a square loop is about 125 W. You must use a matching network to feed a square loop with 50-Ù coax. The rectangular loop achieves gain by compressing its radiation pattern in the elevation plane. The azimuth plane pattern is slightly wider than that of a dipole (it’s about the same as that of an inverted V). A broad pattern is an advantage for a general- purpose, fixed antenna. The rectangular loop provides a

bidirectional gain over a broad azimuth region. Mount the loop as high as possible. To provide 1.7 dB gain at low angles over an inverted V, the top wire must be at least 30 ft high. The loop will work at lower heights, but its gain advantage disappears. For example, at 20 ft the loop provides the same gain at low angles as an inverted V.