A Simple Ring Antenna
Other Factors Affecting Reception.
SWR is not the only indicator of what will and won’t get out on a transmitter. Location and surrounding terrain will also be a major factor. When providing communications for a race, I had two antennas, the ring antenna, and a 5/8 wave mag mount. For one station I could only contact them using the mag mount, while for another station I could only contact them using the ring antenna.
For other ideas on how location can affect reception, read my hub, “The Two Meter Two Step.”
About a year after I got my ham radio license, I got the Amateur Radio license plates for my van. The first thing my Dad said was with those license plates you need to make that thing look like a pincushion. For some operators that is the highest complement that they can be paid. For others, it is a necessary evil. There is an alternative, at least for 2-meter handhelds.
When running mobile on 2-meters, if a hand held radio is all you have, the best an operator can expect with the rubber duck is to hit the local repeater or talk with the car ahead or behind them. Beyond that there are no guarantees. An external antenna can be attached to the radio, but then there is the problem of running a feed line, and looking like a pin-cushion. Realistically, most operators aren't willing to permanently mount a 2-meter antenna to their vehicle for just the handheld, and the hassle of setting up a mag mount often makes it more bother than it's worth.
The alternative I found (kind of by accident) was a quarter wave antenna made from a piece of lanyard cable taped together in a ring. I attached this to a piece of coaxial feed line with an alligator clip and began experimenting. At first testing consisted of holding the antenna up and hitting local repeaters, then I put the ring over the rear view mirror of my vehicle and began trying repeaters further out. I worked simplex with several friends over some fairly long distances and in some pretty rough terrain. Of course, like any antenna it has limits, but it beats the rubber duck and isn't quite as big a hassle to set up.
A quick word about safety. The same precautions need to be taken with regard to RF exposure as should be taken with any antenna. The higher the power, the further away from people the antenna needs to be so DO NOT use this antenna on a mobile rig (any thing above 5 watts) if the antenna is in the vehicle with you. The RF energy can become dangerous at those levels.
When I chose the length for this antenna I used the formula for quad and delta antenna lengths:
Wavelength (in feet) = 1005 / Frequency (in Mhz).
Calculated at 147Mhz this gave me about 6.8 feet. Then I divided by 4 and multiplied by 12 to get a quarter wave in inches. This put the length down to 20.4 inches. I added an inch at one end to attach the feed line making the total length 21.4 inches. I taped one end of the cable against the cable, one inch away from the other end of the cable (there is no connection between the ends of the loop), and then hooked that end to an alligator clip that was attached to the center lead of the coax cable (see diagram).
I used this antenna for a long time before I ever put it on an antenna analyzer (and then I only had a few minutes) but it tuned up at about 146.0 Mhz, with about a 2:1 SWR (which is still better than the rubber duck that comes with most hand-helds). To bring the SWR down try wrapping a loop of wire around the feed line below the alligator clip.
The antenna will of course be somewhat bi-directional (front and back of the ring) but if it is used in a vehicle there should be enough bounce (from all that metal) to get a good signal from any direction. In many vehicles the rear view mirror is attached directly to the windshield. If this is the case, and the car radio antenna is not in the windshield, this antenna can be hung on the rear view mirror. If not, a plastic suction cup can be used to hang it on one of the windows. Hanging the antenna on a window will give the best coverage without changing the properties of the antenna.
One of the joys of amateur radio is experimenting with new ideas. This simple ring antenna is far from perfected. Someday I'll take the time with an antenna analyzer and get it perfect, but for now, it does a pretty good job. At least I don't have to drive around in a pincushion if I don't want to.