IFF Mark II
IFF Mark II was the first operational identification friend or foe system. It was developed by the Royal Air Force just before the start of World War II. Originally ordered in 1939, installation was delayed during the Battle of Britain. It remained in use until 1943, when it began to be replaced by the standardised IFF Mark III.
About IFF Mark II in brief
IFF Mark II was the first operational identification friend or foe system. It was developed by the Royal Air Force just before the start of World War II. The Mark I was a simple system that amplified the signals of the British Chain Home radar systems, causing the aircraft’s ‘blip’ to extend. 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. Originally ordered in 1939, installation was delayed during the Battle of Britain and the system became widely used from the end of 1940. It remained in use until 1943, when it began to be replaced by the standardised IFF Mark III, which was used by all Allied aircraft until long after the war ended. The system proved highly unreliable; it worked only when the aircraft was at certain locations and flying in certain directions. In 1938, researchers at the Bawdsey Manor radar research establishment began working with the first of Robert Watt’s concepts. Known as ‘pip-squeak’, the system worked but was very labour-intensive, requiring operators at several stations and at plotting boards in sector HQs. It also meant pilots were constantly interrupted when talking ground controllers were needed. A small part of the tank’s output is sent back into the tank to provide feedback for the regenerative receiver. As the input signal is relatively constant, a single vacuum tube can provide significant feedback.
One significant problem with regenerative receivers is that if the output is relatively long, the feedback can provide a significant problem if the signal is received back into a small vacuum tube. This is a problem that can be significant with a large number of signals, such as Morse code or Morse code. The idea was to amplify the radio signal and send it into an LC circuit that resonates at a selected frequency. When a pulse from the radar hit them, they would resonate for a short period and cause an additional signal to be received by the station. The antennas were connected to a motorised switch that periodically shorted the antenna out and cancelled the broadcast. On the CH display, this caused the ‘blip’ to periodically lengthen and contract. This led to the introduction of the Pip-Squeak system to provide information from the air defence system to the ground controllers to provide a bird’s-eye view of the airspace. The standard aircraft radios were modified to send out a 1 kHz tone for 14 seconds every minute, allowing the tracking stations ample time to measure the aircraft’’s bearing. Several such stations were assigned to each sector of the air defense system and sent their measurements to a plotting station at sector headquarters. There they used triangulation to determine the Aircraft’s location.
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This page is based on the article IFF Mark II published in Wikipedia (as of Oct. 31, 2020) and was automatically summarized using artificial intelligence.
