Metal garage doors may be solid and secure, but they are not transparent to radio waves. If your garage has aluminum siding, you may experience frustration with the operation of your garage-door opener.
Construction is simple. The antenna is completely passive and uses a J-pole design. The antenna uses readily available 300 ohm flat TV twin-lead and RG-174 50 ohm miniature coaxial cable. The length suits an opener that operates at 310 MHz. Most popular openers, such as Stanley, Genie, and Chamberlain, operate at this frequency. However, some units operate at 315 MHz, some replacement controls operate at 390 MHz, and some automobile manufacturers offer 380-MHz designs. You can usually find the operating frequency in the user’s manual, or you can obtain it directly from the manufacturer.
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