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High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate over long distances; for example, between U-boats and their land-based headquarters.
A smart doorbell is an internet-connected doorbell that notifies the home owner on his or her device (smartphone or any other gadget) when a visitor arrives at the door. It activates when the visitor presses the button of the doorbell, or alternatively, when the doorbell senses a visitor with its built-in motion sensors. The smart doorbell lets ...
Initially three U Adcock HF DF stations were set up in 1939 by the General Post Office. With the declaration of war, MI5 and RSS developed this into a larger network. One of the problems with providing coverage of an area the size of the UK was installing sufficient DF stations to cover the entire area to receive skywave signals reflected back ...
For this reason, Doppler DF systems normally mount their antennas on a small disk that is spun at a high speed using an electric motor. Performing the same calculation using an antenna mounted to a disk with a diameter of 50 centimetres (20 in) diameter spinning at 1000 Hz results in: S = .25 × 1000 × 101.8 / 48 = 530 Hz
Doorbell at the entrance of Chetham's Library, Manchester, England Sound of a two-tone mechanical doorbell. A doorbell is a signaling device typically placed near a door to a building's entrance. When a visitor presses a button, the bell rings inside the building, alerting the occupant to the presence of the visitor. Although the first ...
Radio direction finding equipment for eighty meters, an HF band, is relatively easy to design and inexpensive to build. Bearings taken on eighty meters can be very accurate. Competitors on an eighty-meter course must use bearings to determine the locations of the transmitters and choose the fastest route through the terrain to visit them.
The AN/FLR-9 Operation and Service Manual [2] describes the array as follows: . The antenna array is composed of three concentric rings of antenna elements. Each ring of elements receives RF signals for an assigned portion of the 1.5 to 30-MHz radio spectrum.
Maxwell K. Goldstein (January 15, 1908 – February 18, 1980) was a first generation Jewish-American scientist and engineer who was instrumental in the development and deployment of high-frequency direction finding by the United States Navy during the Second World War.