There is no other band that is affected by as many forms of propagation as 6m (50 MHz). Sporadic-E (Es) in summer and winter. 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 2m or 70cm band, you can do surprisingly long distances at 6m. Even EME is operated at 6m. 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 6m 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 on 6m.
Participate with limited resources
Now you would think that you would at least need a large directional antenna to be able to participate in DX. For example, on QRZ.com you can see stations on the 6 meter band with large antenna installations. From cubical quads to stacked yagis which pick up weak signals well. Thanks to these stations you can participate with only limited resources. With limited resources I mean a hula hoop, some speaker wire and an SO-239 connector. Get ready to build your classic halo antenna.
Better than a vertical
In a previously published article I already wrote about the dual band square halo for 10m and 20m. The halo is an omnidirectional radiator with horizontal polarization. In contrast to a vertical, the gain of the halo at low beam angles up to about 5° (necessary for DX) increases with height above the ground. At a wavelength above the ground, the halo already produces a few dB more gain than a vertical. Next to that, almost every DX station uses 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 so easy to build yourself. The other variant is the classic halo; the antenna that was patented as the original halo in 1946.
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. That circular shape makes it nearly omnidirectional. It also lowers the impedance of the folded dipole from 300 ohms to 50 ohms. Impedance matching is not necessary, saving parts. In addition, the classic halo is more broadband than the modern halo. In practice on I measured about 15% more on 10m band.
In a square shape
Now the halo is very flexible, because in addition to a circular shape, the halo also works great if you place it in a square shape. Even then the impedance is 50 ohms. Such a square halo is also popularly called ‘Squalo’, a combination of ‘square’ and ‘halo’.
Making your own halo is so easy
Making your own halo is so easy (I do not understand that this type of antenna is not used more commonly as a limited space DX antenna solution). You can choose between a circular or square shape. I chose the circle shape for oy 6m version, because the materials for it are easy to obtain.
Folded speaker cable dipole
Starting with the folded dipole. You can take speaker cable for this. For example 2x 0.75mm2 (#18 AWG) is fine. You take half a wavelength of wire, a little over 3 meters (118″) in this case. Connect (solder) the ends together. Then cut one of the two wires in the middle. You solder one wire to the core of your coax and the other to the shield. Make it waterproof with a little nail polish. Or you 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
In the local sale store, I found that a hula hoop is almost the perfect size for a halo. That frivolous blue and white striped hoop was the inspiration for this halo project. For 3 euros I had a hoop with a diameter of 0.89 meters (36″). A diameter of 0.89 meters x Pi gives a circumference of 2.8 meters (110″). Almost perfect for the 3 meter (118″) wide folded dipole. Now there are also hoops that are slightly larger or smaller. Then you can also choose to put your saw in 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 16mm polyethylene hose with a straight coupling that you buy at the hardware store. This hose is commonly used as a flexible plastic water pipe and is easy to bend.
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 euro cents. On one side I have attached two so-called 16mm (5/8″) Stauff pipe clamps. The piece of 5/8” PVC pipe fits nicely in there. By the way, you can also use other pipe clamps for 5/8” or another diameter. On the other side I mounted an exhaust pipe clamp to attached it onto mast.
Keepin’ it horizontal with a brace
Now that hoop does not stay horizontal by itself. To support the hoop, take 1.5 meters of PVC pipe to serve as a brace. At the ends of the tube you screw a small screw eye. Then attach the PVC tube to the mast and to the other side of the hoop with cable ties via the screw eyes. Apart from a PVC pipe, you can of course use any other non-conductive material. A broomstick also works fine…
Tune the dipole by folding back its ends
The tuning is done by varying the length of the dipole. This is easiest if you first fold the ends of the dipole back about five centimeters. Then adjust the folded back length until the halo is optimally tuned. Most DX on 6m roughly 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 at the plug approximately four times with a maximum diameter of 8cm (3″). That should already be quite effective. You can also use some ferrite beads material #43
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 beam angles. Especially on the 6 meter band, the signals with a low beam angle are the most valuable. Besides that it is of course always better if your antenna looks out above the roofs. So get this antenna as high as possible.
My personal experiences
I made my hula hoop halo in just under an hour. Then I mounted it on a fiberglass mast about 8 meters above the ground. After initially only a few connections within the Netherlands and Belgium and a few to the English east coast, the Es season started at the end of April 2021. I could easily work across Europe, northern Africa and Middle East. I even managed to work stations along the US East Coast in one evening with 25 watts.
In short, the hula hoop halo is perhaps the most inexpensive way to start on the 6 meter band. My total costs were about 12 euros (15 USD).