Looking for a cheap and easy to build 6 meter wire antenna with good performance that fits into a small space? How about a Hentenna? The Hentenna was developed in Japan in the early 1970’s. Because of the strange characteristics the antenna exhibits, the Japanese word for strange, “hen”, was substituted for the “an” in antenna and it became known as the Hentenna.
The modeled dimensions for a horizontally polarized 6 meter Hentenna optimized for operation between 50.1 to 50.6 MHz are shown in Figure-1. The modeled antenna elements are made of #15 AWG bare aluminum fence wire. The lower end of the antenna is approximately 5′ above average ground. The antenna is tuned by sliding wire 4 up or down as needed to obtain the lowest SWR. The antenna feed point is the center of wire 4. The model produced the best SWR curve when a 2:1 balun was inserted at the feed point. The modeled transmission line consisted of 25′ of RG-8X coax.
If the antenna is mounted long sides up, the resulting RF field is horizontally polarized. If it is mounted long sides parallel to the ground, the resulting RF field is vertically polarized. Antenna gain is relatively high and take-off angle is low. Figure-1 is a diagram of the antenna.
Figure-2 depicts the modeled antenna’s predicted radiation pattern at 50.2 MHz. Click the image to display it full size.
Figure-3 is a bar graph of the predicted SWR for the frequency range 50.1 – 50.6 MHz. Click the image to see display it full size.
1. Consider using #15 AWG bare aluminum fence wire and porcelain “standoff” insulators to build the antenna. The wire and insulators can be purchased from your local farm supply outlet. Using bare aluminum wire facilitates the tuning process. Tuning is performed by sliding wire 4 up or down to achieve the best SWR curve. You can make wire 4 (tuning wire) using set screw type lug connectors at either end. Make sure you keep wire 4 as level as possible and move each end the same amount during the tuning process. Don’t forget to insert the loop wire through the set screw lugs and position the wire 4 lugs above the lower porcelain insulators before the loop is tightened and connected at the bottom. You can use a small aluminum turnbuckle to connect and tighten the wire loop at the bottom. The tuning process will compensate for the insertion of the turnbuckle. If you need to optimize tuning for different portions of the 6 meter band, record the vertical distances of each optimal tuning point in a table or mark them on the long support member in different colors. To re-position wire 4, loosen the set screws, move the lugs to the desired colored position, and tighten the set screws.
2. When you build the supporting frame for the wire, consider providing a center support member to relieve the strain on adjustable wire 4 (feed point) especially if you are using a balun otherwise the combined weight of the balun and transmission line will cause wire 4 to sag in the middle. You can use a zip tie around the balun and center support to secure the balun in place when tuning is complete. If you need to re-position wire 4 to tune for different portions of the 6 meter band, use an adjustable garden clamp to secure the balun so it can be easily moved.
3. With a little work, the antenna can be made manually rotatable using 1″ diameter galvanized pipe inserted into a 4′ section of 1 1/4″ diameter galvanized pipe embedded in a concrete pedestal. It is easy to build a square wood form and make the pedestal using fast setting concrete. Grease the lower 4′ of the 1″ diameter pipe with good quality lithium grease to ensure easy rotation and retard rust formation. Drill and tap the 1 1/4″ section of pipe near the top to accept a 1/4″ X 20 TPI cap bolt. Tighten the cap bolt to prevent “freewheeling.” Attach a split pipe clamp threaded for a bolt to the 1 1/4″ fixed section of pipe to serve as a reference pointer to North. Use a compass to find magnetic North. If you need the antenna to be positioned relative to true North, use the link below to find the declination for your latitude/longitude. Add or subtract the declination to your magnetic North compass bearing to determine true North. Rotate the clamped index pointer to the North you have selected (magnetic or true) and tighten it. You can also add a split pipe clamp threaded for a bolt to the 1″ diameter rotating mast to serve as a bearing pointer relative to the North index pointer attached to the fixed lower section of pipe.
4. The 6 meter Hentenna has a relatively small footprint. You can clamp the outer 1 1/4″ pipe to the corner of a deck or a length of pressure treated 4 X 4 buried in the ground. Use a threaded pipe cap attached to the lower end of the outer pipe to keep the rotating mast from dropping through the bottom.
5. By adding a motor driven antenna rotator, you can easily convert the Hentenna into a remotely controlled rotatable antenna. A TV antenna rotator can easily provide the necessary torque to rotate the antenna.
The EZNEC and AutoEZ models referenced in this article can be downloaded from the link below in zipped format. EZNEC provides the capability to view radiation pattern polarization components (horizontal and vertical) in different colors. Check the EZNEC user manual for instructions on how to display radiation polarization.