Search results
Results from the WOW.Com Content Network
The magnetic detector or Marconi magnetic detector, sometimes called the "Maggie", was an early radio wave detector used in some of the first radio receivers to receive Morse code messages during the wireless telegraphy era around the turn of the 20th century.
The CF UGS systems employ various sensor modalities including seismic, acoustic, magnetic, and pyroelectric transducers, daylight imagers and passive infrared imagers to automatically detect the presence of persons or vehicles, and transmit activity reports or imagery via radio-frequency (RF) or satellite communications (SATCOM) links to a ...
Higher radio frequencies thus require more poles, a higher rotational speed, or both. Alexanderson alternators were used to produce radio waves in the very low frequency (VLF) range, for transcontinental wireless communication. A typical alternator with an output frequency of 100 kHz had 300 poles and rotated at 20,000 revolutions per minute ...
Electronic article surveillance antennas at an H&M store in Torp shopping mall, Sweden. Electronic article surveillance (EAS) is a type of system used to prevent shoplifting [1] from retail stores, pilferage of books from libraries, or unwanted removal of properties from office buildings.
In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage. The term dates from the first three decades of radio (1888–1918). The term dates from the first three decades of radio (1888–1918).
Systems may also include visual aids, such as LED or LCD readouts to indicate object distance. A vehicle may include a vehicle pictogram on the car's infotainment screen, with a representation of the nearby objects as coloured blocks. Rear sensors may be activated when reverse gear is selected and deactivated as soon as any other gear is selected.
British explorer Sir James Clark Ross discovered the magnetic north pole in 1831 in northern Canada, approximately 1,000 miles (1,609 kilometers) south of the true North Pole.
Due to their omnidirectional radiation pattern, vertical monopole antennas are commonly used in terrestrial radio communication systems in which the direction to the transmitter or receiver is unknown or constantly changing, [7] such as broadcasting, mobile two-way radios, and wireless devices like cellphones and Wi-fi networks, [8] [4] because they radiate equal radio power in all horizontal ...