H

HDOP

Dilution of precision (DOP), or geometric dilution of precision (GDOP), is a term used in satellite navigation and geomatics engineering to specify the additional multiplicative effect of navigation satellite geometry on positional measurement precision. Due to the relative geometry of any given satellite to a receiver, the precision in the pseudorange of the satellite translates to a corresponding component in each of the four dimensions of position measured by the receiver (i.e., x, y, z, and t). The precision of multiple satellites in view of a receiver combine according to the relative position of the satellites to determine the level of precision in each dimension of the receiver measurement. When visible navigation satellites are close together in the sky, the geometry is said to be weak and the DOP value is high; when far apart, the geometry is strong and the DOP value is low. Consider two overlapping rings, or annuli, of different centres. If they overlap at right angles, the greatest extent of the overlap is much smaller than if they overlap in near parallel. Thus a low DOP value represents a better positional precision due to the wider angular separation between the satellites used to calculate a unit's position. Other factors that can increase the effective DOP are obstructions such as nearby mountains or buildings. DOP can be expressed as a number of separate measurements. HDOP, VDOP, PDOP, and TDOP are respectively Horizontal, Vertical, Position (3D), and Time Dilution of Precision.

View Source: https://en.wikipedia.org/wiki/Dilution_of_precision_(GPS)

Helical Antenna

A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. In most cases, helical antennas are mounted over a ground plane. The feed line is connected between the bottom of the helix and the ground plane. Helical antennas can operate in one of two principal modes — normal mode or axial mode. In the normal mode or broadside helix, the dimensions of the helix (the diameter and the pitch) are small compared with the wavelength. The antenna acts similarly to an electrically short dipole or monopole, and the radiation pattern, similar to these antennas is omnidirectional, with maximum radiation at right angles to the helix axis. The radiation is linearly polarised parallel to the helix axis. In the axial mode or end-fire helix, the dimensions of the helix are comparable to a wavelength. The antenna functions as a directional antenna radiating a beam off the ends of the helix, along the antenna's axis. It radiates circularly polarised radio waves.

View Source: http://en.wikipedia.org/wiki/Helical_antenna

HGA

A high-gain antenna (HGA) is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna. Most commonly referred to during space missions, these antennas are also in use all over Earth, most successfully in flat, open areas where no mountains lie to disrupt radiowaves.

View Source: https://en.wikipedia.org/?title=High-gain_antenna

High-gain

A high-gain antenna (HGA) is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna. Most commonly referred to during space missions, these antennas are also in use all over Earth, most successfully in flat, open areas where no mountains lie to disrupt radiowaves.

View Source: https://en.wikipedia.org/?title=High-gain_antenna

Hysteresis

Hysteresis is the time-based dependence of a system's output on current and past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known.

View Source: https://en.wikipedia.org/wiki/Hysteresis