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Umbrella antennas are good ground wave antennas, and are used as radio broadcasting antennas in the MF and LF bands. The gain of an umbrella antenna over perfectly conducting ground, like other electrically short monopole antennas, is approximately 3.52 dBi if it is significantly shorter than 1 4 λ . {\displaystyle {\tfrac {1}{4}}\lambda ~.}
A helical antenna is an antenna consisting of one or more conducting wires wound in the form of a helix.A helical antenna made of one helical wire, the most common type, is called monofilar, while antennas with two or four wires in a helix are called bifilar, or quadrifilar, respectively.
Sticherus cunninghamii, also known as umbrella fern, is a New Zealand endemic fern. The species is named after English botanist and explorer Allan Cunningham ; its Māori names include rarauheriki , waekura and tapuwae-kōtuku .
For a monopole antenna (a), the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from a virtual "image antenna" (b).In Telecommunications, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements.
The mounting screw is hollow and has two lateral holes to attach a plumb bob to center the instrument e.g. over a corner or other mark on the ground. After the instrument is centered within a few cm over the mark, the plumb bob is removed and a viewer (using a prism ) in the instrument is used to exactly center it.
Screw (helical) nail – a nail with a spiral shank - uses including flooring and assembling pallets; Shake (shingle) nail – small headed nails to use for nailing shakes and shingles; Sprig – a small nail with either a headless, tapered shank or a square shank with a head on one side. [27]