SWL Receiving longwire antenna

 

Figure  shows the common receiving longwire. The antenna element should be 30 to 150 ft in length. Although most texts show it horizontal to the ground (and indeed, a case can be made that performance is better that way), it is not strictly necessary. If you must slope the wire, then it is doubtful that you will notice any re- ception problems. The far end of the wire is attached to a supporting structure through an insulator and a rope. The support structure can be another building, a tree, or a mast installed especially for this purpose. Chapter 28 deals with antenna construction practices.

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.