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Materials
A tri-band patch antenna employs coaxial cable with a locking "N" connector that screws and locks to a scanner or ham radio antenna connector. Soldered to the other end of this short coaxial stub is a 300-ohm cable, the same type used in older television antenna installations before coaxial cable largely took over. A small notch cut on one side of the 300-ohm lead creates a band-pass filter. You can make these antennas as long as necessary, but they typically range from 6 to 8 feet in length.
Flexibility
You can use this antenna in installed spaces, permanently connected to the radio. Alternately, tri-band patch antennas often serve as spare units, coiled and thrown into a bag for ham radio field days. You can hang them over a tree branch for extended range or keep them coiled into a tight loop for portable radio use.
Construction
A 3- to 4-inch-long RG-58 coaxial cable has its copper center conductor and braided shield twisted into a tight pigtail and soldered to the two individual wire leads on the 300-ohm cable, which has a small notch cut into one side. About 15 inches from the soldered connections, this notch serves as a band-pass filter. Heat-shrink tubing or electrical tape then seals the connections.
Range and Performance
A solidly built tri-band antenna can receive signals up to 75 miles away, when not limited by surrounding buildings and terrain, as well as solar flares and weather conditions. Key in solid reception is ensuring that the center conductor and twisted shield don't come into contact, and that the mounting hardware, such as tacks or brads, don't touch the 300-ohm lead wires.