There seems to be some renewed interest in the Big Wheel Antenna. It’s a really great omni antenna for the 2M band. The design is such that it can be scaled to make smaller (or larger) Wheels for use on other VHF/UHF bands. The RMVHF+ Group is using them on the four bands of beacons; 2M, 1.35M, 70cm and 33cm. I use one when I’m the Net Control station on the ‘groups’ 2M Monday evening net, in conjunction with my 36 element array (4 X 9M2’s). I can hear the check-ins quite well with it from Cheyenne to Pagosa Springs and Grand Junction to Smith Center, KS but the copy is considerably better with the array. The omni is great for out to about a 100 mile radius.
Time has gotten past us for any recent publication of the construction of the Wheel antennas. The ARRL’s last mention of them was in the early ‘70’s “Handbook”. Information on them can be found in some of the old ARRL VHF Manuals (late 60’s early 70’s). I guess no one believes in using an omni for local VHF work anymore. Everyone must be working all that DX on 2M with their long yagis! I find it interesting when I see some enormously long 2M yagi on a roof or tower that is vertically polarized, what a waste! Ya’ know they are using it to work some FM repeater maybe 30 miles away that could just as easily be worked with 10 watts and a ground plane (stinger). Trying to work SSB on 2M with those long yagis vertically polarized, they might as well be using a wet noodle. The polarization loss will be on the order of 22 dB. Please, when operating SSB on the 2M and higher bands use horizontal polarized yagis and omnis. But that’s not the intent of this paper. Let me get into the “Rerolling of the Wheel”.
Although I have designed and manufactured hundreds of Wheels for as low in frequency as TV Chan 2 and as high as the 5.7 GHz ISM band, I am not the original designer. W1FVY and W1IJD were the developers of the Big Wheel (for the 2 meter band) back in the 60’s. I first started building and using the Big Wheel in the early 70’s for mobile 2M terrestrial and satellite work as the Wheel is circularly polarized above and below its horizontal plane. In the horizontal plane the Wheel exhibits a gain of a couple of dB more than the common resonate dipole (and even the Turnstile). These antennas can be stacked as a pair to obtain 5 dBd and as a quad array of four for ~8 dBd.
Those of you that have never seen a Wheel antenna let me explain, they look like a shamrock or three leaf clover when looking down on them, or up at one toward the bottom of it. The elements (of which three are required) can be constructed of aluminum rod or tubing (3/8” to 1/2” dia.) and 80” in length. Mark 20” in from each end and bend them at those points with a 6” radius to form one of the elements which will look like the skeleton of a single clover leaf. The roundness of the 40” portion that is in between the 20” sections can be formed by hand. I’ve been accused of and found guilty of having ‘educated fingers’ in constructing the elements for Wheels at the higher frequencies. I’ve never used a jig to do the forming. In each element end drive in an appropriate diameter length of hard wood dowel rod, about an inch or so. Drill a #8 hole perpendicular to the plane of the element a half inch back from the end. Do this to both ends of all three elements.
The elements are attached to a hub which consists of a pair of 4″ aluminum, 1/8” thick, discs. They will be spaced1.5″ apart using a shorting strap. This shorting strap will need to be fashioned from a 5” length of 1” wide, 1/8” thick aluminum stock. Drill a #8 hole at each end of it, on center and 1/4” in from the ends. Bend this strap into a “U” shape so that the open ends are approximately 1-3/4” apart.
Lay out the pair of discs by placing 3, #8 holes equally spaced around the periphery of the discs and a half inch in from the edge. Then between two of the #8 holes, drill another #8 hole but in from the edge only 1/4″. These holes are to be used to hold the “U” shaped shorting strap. Then in the center of one of the discs drill a #8 hole. In the center of the other disc drill or punch a hole to fit a coax connector of your choice. This will be referred to as the bottom disc. From the center conductor of this coax connector solder a length of #8, brass ‘all thread’ or a long #8, copper or brass screw that will be secured to the top disc with the appropriate brass or copper nuts, one on each side of the disc.
The elements can now be installed on this hub. Place one of the ends of an element on the bottom disc and secure it to that disc at one of the holes provided. The other end of this element will be secured to the top disc. The first end of the second element will be secure to the bottom disc right below the second end of the first element. Then the second end of the second element will attach to the top disc at the hole provided. Follow suite with the third element.
An “L” bracket can be fashioned from 1” X 8” X 1/8” aluminum strap (bend to 90° at the 4” point) and secured to the bottom disc using any of the screws for mounting, and hose clamp to a pole or mast.
That is basically all there is to the construction or the ‘Rolling of a Wheel’. Testing and adjusting is accomplished by mounting the Wheel about 6’ in the air attach a convenient length of coax to the Wheels’ coax connector and to an antenna analyzer such as an MFJ. Find where the Wheel is resonate. You’d like it to be in the vicinity of 144.2. If the resonate point is below this frequency, take an element in both hands near the bottom disc and bend it down slightly. Do this to all three elements. Check the resonate point again. If it is still low in frequency, take an element that is attached to the top disc, again with both hands, and bend it up slightly. The Wheel is fairly broad and should not require too much tuning. If the frequency is higher than 144.2, bend the elements so that the spokes are closer together in the vertical plane. The tuning can also be done with a transmitter and VSWR bridge. Once the VSWR is 1.5:1 or less at 144 or 144.2, leave it alone! There is nothing to be gained by getting the antenna any closer to a 1.0:1 VSWR.
Dave W6OAL –
Olde Antenna Laboratory 41541 Dublin Drive Parker, CO 80138