Rubber ducky antenna

The rubber ducky antenna (or rubber duck aerial) is an electrically short monopole antenna that functions somewhat like a base-loaded whip antenna. It consists of a springy wire in the shape of a narrow helix, sealed in a rubber or plastic jacket to protect the antenna. Rubber ducky antenna is a form of normal-mode helical antenna. Electrically short antennas like the rubber ducky are used in portable handheld radio equipment at VHF and UHF frequencies in place of a quarter wavelength whip antenna, which is inconveniently long and cumbersome at these frequencies. Many years after its invention in 1958, the rubber ducky antenna became the antenna of choice for many portable radio devices, including walkie-talkies and other portable transceivers, scanners and other devices where safety and robustness take precedence over antenna capabilities. The rubber ducky is quite flexible, making it more suitable for handheld operation, especially when worn on the belt, than earlier rigid telescoping antennas. Two rumors link the naming of the antenna with the Kennedy family. In the early 1960s the rubber ducky became the antenna of choice for personal walkie-talkie transceivers used by police and security services, including the U.S. Secret Service, which guards the President of the United States. According to one rumor, the young Caroline Kennedy, daughter of President John F. Kennedy, named the flexible device when she pointed at one on an agent's transceiver and said, 'rubber ducky'. On the other hand, Dr. Thomas A. Clark, a senior scientist with NASA, claims to have named it after listening to one of Vaughn Meader's comedies about the Kennedy family. An alternative name is based on the short stub format: the 'stubby antenna'. Before the rubber ducky, antennas on portable radios usually consisted of quarter-wave whip antennas, rods whose length was one-quarter of the wavelength of the radio waves used. In the VHF range where they were used, these antennas were 2 or 3 feet (0.60 to 0.91 meter) long, making them cumbersome. They were often made of telescoping tubes that could be retracted when not in use. To make the antenna more compact, electrically short antennas, shorter than one-quarter wavelength, began to be used. Electrically short antennas have considerable capacitive reactance, so to make them resonant at the operating frequency an inductor (loading coil) is added in series with the antenna. Antennas which have these inductors built into their bases are called base-loaded whips. The rubber ducky is an electrically short quarter-wave antenna in which the inductor, instead of being in the base, is built into the antenna itself. The antenna is made of a narrow helix of wire like a spring, which functions as the needed inductor. The springy wire is flexible, making it less prone to damage than a stiff antenna. The spring antenna is further enclosed in a plastic or rubber-like covering to protect it. The technical name for this type of antenna is a normal-mode helix. Rubber ducky antennas are typically 4% to 15% of a wavelength long; that is, 16% to 60% of the length of a standard quarter-wave whip. Because the length of this antenna is significantly smaller than a wavelength the effective aperture, if 100% efficient, would be approximately: Like other electrically short antennas the rubber ducky has poorer performance (less gain) due to losses and thus considerably less gain than a quarter-wave whip. However it has somewhat better performance than an equal length base loaded antenna. This is because the inductance is distributed throughout the antenna and so allows somewhat greater current in the antenna.