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The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
Parallel-wire line (the generic sense of twin lead) is supplied in several different sizes, with values of 600 Ω, 500 Ω (ladder line), 450 Ω, 350 Ω (window line), 300 Ω (window line, ribbon cable), and 75 Ω (ribbon cable) characteristic impedance.
They are intermediate in size and function between small and large loops, and are often described as a half-wavelength dipole that has been bent from a straight line into a round circle, but with its far ends left unconnected. [3] [11] [2] [4] (pp 231–275)
Via fences use up a lot of valuable substrate real estate and so will increase the overall size of the assembly. Via fences too close to the line being guarded can degrade the isolation otherwise achievable. In stripline, a rule of thumb is to place the fences at least four times the trace to groundplane distance away from the line being ...
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Single-person post pounders tend to be around 20 pounds (9 kg), but weight varies with model types. The diameter depends on the size of the post to be pounded. They can be dangerous to handle, especially if the lower edge of the pounder catches on the top of the post, when it can pivot towards the user and strike them on the head.
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The folded unipole antenna was first devised for broadcast use by John H. Mullaney, an American radio broadcast pioneer, and consulting engineer. [2] It was designed to solve some difficult problems with existing medium wave (MW), frequency modulation (FM), and amplitude modulation (AM) broadcast antenna installations.