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  2. Air changes per hour - Wikipedia

    en.wikipedia.org/wiki/Air_changes_per_hour

    Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each ...

  3. Heating, ventilation, and air conditioning - Wikipedia

    en.wikipedia.org/wiki/Heating,_ventilation,_and...

    For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which has thousands of changes per ...

  4. Radio button - Wikipedia

    en.wikipedia.org/wiki/Radio_button

    A radio button or option button[citation needed] is a graphical control element that allows the user to choose only one of a predefined set of mutually exclusive options. [1] The singular property of a radio button makes it distinct from checkboxes, where the user can select and unselect any number of items.

  5. E6B - Wikipedia

    en.wikipedia.org/wiki/E6B

    E6B. The front of a metal E6B. The E6B flight computer is a form of circular slide rule used in aviation. It is an instance of an analog calculating device still being used in the 21st century. An E6B flight computer commonly used by student pilots. They are mostly used in flight training, because these flight computers have been replaced with ...

  6. Free-space path loss - Wikipedia

    en.wikipedia.org/wiki/Free-space_path_loss

    Free-space path loss. In telecommunications, the free-space path loss (FSPL) (also known as free-space loss, FSL) is the attenuation of radio energy between the feedpoints of two antennas that results from the combination of the receiving antenna's capture area plus the obstacle-free, line-of-sight (LoS) path through free space (usually air). [1]

  7. Radar horizon - Wikipedia

    en.wikipedia.org/wiki/Radar_horizon

    Radar horizon. The radar horizon is a critical area of performance for aircraft detection systems, defined by the distance at which the radar beam rises enough above the Earth 's surface to make detection of a target at the lowest level possible. It is associated with the low elevation region of performance, and its geometry depends on terrain ...

  8. Airflow - Wikipedia

    en.wikipedia.org/wiki/Airflow

    In engineering, airflow is a measurement of the amount of air per unit of time that flows through a particular device. It can be described as a volumetric flow rate (volume of air per unit time) or a mass flow rate (mass of air per unit time). What relates both forms of description is the air density, which is a function of pressure and ...

  9. Amateur radio licensing in the United States - Wikipedia

    en.wikipedia.org/wiki/Amateur_radio_licensing_in...

    Amateur First Grade required an essay-type examination and five (later ten) words per minute code examination before a Radio Inspector at one of the Department's field offices. This class of license was renamed Amateur Class in 1927 and then Amateur First Class in 1932. Amateur Radio licensing in the United States began in mid-December 1912.