There is no other band that is affected by so many forms of propagation as 6 meters (50 MHz). Sporadic-E (Es) in summer and midwinter. TEP (transequatorial propagation) around March/April and September/October. F2 propagation and aurora in periods of high solar activity. Meteorscatter and the almost daily present troposcatter. But even in tropo conditions, where most radio amateurs switch to the 2 meter or 70 centimeter band, you can do surprisingly long distances on 6 meters. Even EME is done on this band. The 6 meter band is therefore rightly called ‘The Magic Band’.
DX up to 10,000km and more
For me personally, the most spectacular propagation on 6 meters is the annual multi-hop sporadic-E. This propagation occurs mainly in late spring and early summer. In the Northern Hemisphere from May to July and in the Southern Hemisphere from November to January. With multihop Es, DX up to 10,000 kilometers (6,000 miles) and more is possible.
Participate with limited resources
On QRZ.com you see stations with large antenna installations for 6 meters. From cubical quads to arrays of stacked yagis. You would think that you need a large directional antenna to be able to join in, but that is certainly not necessary. Those large directional antennas you see on QRZ.com can pick up weak signals easily. So you only thing you have to do is put that signal out. You can do that with only limited resources. With limited resources I mean a hula hoop, some speaker wire and SO-239 socket. Get ready to build your own classic halo antenna.
Better than a vertical
In a previously published article I wrote about the dual band square halo for 10 meter and 20 meter band. The halo is an omnidirectional radiator with horizontal polarization. In contrast to a vertical, the gain of the halo at radiation angles up to about 5 degrees (good for DX), increases with height above the ground. At only one wavelength above ground, the halo already produces a few dB more gain than a vertical antenna. Next to that, 99% of DX stations use horizontal polarization. The principle of the halo can be applied to any amateur frequency, including 50 MHz.
Modern vs. classic halo
The halo comes in two variants. The most commonly used variant among radio amateurs is the modern band halo with gamma match, mainly used on VHF. It is easy to tune, but not that easy to build. The other variant is the classic halo; the antenna that was patented as the original halo back in 1946.
(image from qsl.net/kp4md).
Nothing more than a folded dipole
The classic halo is nothing more than a folded dipole, not stretched, but put into a circular shape, with some open space between the dipole ends. Impedance matching is not necessary. You can feed the halo with any 50 ohm coax. In addition, the classic halo is more broadband than the modern halo. I measured about 15% more compared to the halo with gamma match.
In a square shape
The halo is very flexible. In addition to a circular shape, the halo also works great if you place it in a square shape. Then the feedpoint impedance is still 50 ohms. Such a square halo is also popularly called ‘Squalo’, a combination of ‘square’ and ‘halo’.
Making your own halo is so easy
For me personally, it’s difficult to understand why this type of antenna is not used more commonly as a limited space DX antenna solution. The classic halo is such an easy to build antenna. I chose the circle shape for the 6m version. The materials for it are easy to obtain.
Folded speaker cable dipole
Starting with the folded dipole. You can use speaker cable for this. For example 2x 0.75mm2 (#18 AWG) is fine. You take half a wavelength of wire, a little over 3m (118″) in this case. Connect (solder) the ends together. Then cut one of the two wires in the middle. Solder one wire to the core of your coax and the other to the shield. You make it weatherproof with a little nail polish. Or solder the wires to a SO-239 chassis socket or attach ring connectors to a dipole center connector.
The hoop or polyethylene hose as spreader
Wandering around in a local outlet store, I saw a hula hoop that that had almost the perfect size for a halo. The frivolous blue and white striped hoop became the inspiration for this 6 meter band halo antenna project. For 3 euros I had a hoop with a diameter of 0.89 meters (36″). A diameter of 0.89m x Pi makes a circumference of 2.8m (110″). Almost perfect for the 3m (118″) wide folded dipole. Now there are also hoops that are slightly larger or smaller. Then you can choose to put your saw in it to shorten or lengthen it. In the hoop I bought I was able to slide exactly a 5/8” PVC pipe in, to extend the hoop a little. Instead of a hoop you can also use polyethylene water supply or irrigation pipe. With a straight coupling you can connect the ends of the polyethylene pipe and bend it into a circular shape.
The halo on the mast with a cutting board
You can attach the folded dipole to the hoop with some cable ties. To make a mast attachment, I bought a small plastic cutting board, 24cm x 14cm (10″ x 6″) from a local store for just 59 eurocents. On one side I attached two so-called 16mm (5/8″) Stauff pipe clamps. You can use any other pipe clamps for 5/8” or a different diameter. The piece of 5/8” PVC pipe fits nicely in there.
On the other side I mounted an exhaust pipe clamp to attach it onto a mast.
Keeping it horizontal with a brace
The hula hoop does not stay horizontal by itself, so you need to make a diagonal brace to keep it upright. About 1.5m (5 ft) of PVC electrical pipe can serve as a brace. At the ends of the tube drill a 5-6mm (1/4″) hole. Then attach the PVC tube to the mast and to the other side of the hoop with cable ties through those holes. Apart from a PVC pipe, you can use any other (preferable non-conductive) material. A broomstick or billiard cue works fine as well.
Tune the dipole by folding back its ends
The tuning is done by varying the length of the dipole. Easiest way is to first fold the ends of the dipole back about 5cm (2″). Then adjust the folded back length until the halo is optimally tuned. Most DX on 6 meters takes place between 50.0 and 50.5 MHz.
Common mode choke
To prevent common mode currents on your coax, you can make a simple common mode choke for this antenna from its coax cable. Just roll up the coax (like RG-58 or RG-213) close the PL-plug approximately four times with a maximum diameter of 6-10cm (3-4″). That should already be quite effective.
The higher the better
As mentioned earlier in this article, the halo is a horizontally polarized antenna. With horizontally polarized antennas, the ground below affects the radiation pattern. The higher above the ground, the less the influence, the stronger the signal in the low radiation angles. Especially on the 6 meter band, the signals with a low radiation angle are the ones we need. Besides that, it is of course always better if your antenna looks out above the roofs and trees. So get this antenna as high as possible.
My personal experiences
I made my hula hoop halo in just under an hour. I mounted it on a fiberglass mast, about 8 meters above the ground. After initially only a few connections within my country (The Netherlands) and Belgium and a few to the English east coast, the Es season took off. I could easily work across Europe, northern Africa and Middle East. To my own surprise, I managed to work different stations in FT8 along the US East Coast in one evening. With only 25 watts.
In short, the hula hoop halo is perhaps the most inexpensive way to start your adventures on the 6 meter band. Not only at home, but also for SOTA, POTA and other portable adventures. My total costs were about 12 euros (15 USD).