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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.
HF/DF provides a direct and immediate indication of the signal direction, but only at the cost of requiring an oscilloscope or similar display system with an equally fast response time. Both require two closely matched receivers and amplifiers, and often a third for the "sense" antenna if used.
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.
Mark II addressed both these problems. An automatic gain control eliminated the need to adjust the gain, making the device much more likely to be working properly when interrogated. To work with many types of radar, a complex system of motorised gears and cams constantly shifted the frequency through three wide bands, scanning each every few ...
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.
Thus German records stress the relevance of radar, and not of seaborne HF/DF. Both radar and HF/DF (and ASDIC ) were vital electronic techniques in the defeat of the U-boats, but HF/DF had the advantage of being able to determine the bearing of a U-boat at a range far greater than seaborne radar could achieve.
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 ...