Gillham code: Difference between revisions

Revision as of 18:00, 22 May 2020

Revision as of 18:07, 22 May 2020

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The ''Gillham interface'' and ''code'' are an outgrowth of the 12-bit [[IFF Mark X]] system, which was introduced in the 1950s. The civil [[transponder interrogation mode (aviation)|transponder interrogation mode]]s [[Mode A|A]] and [[Mode C|C]] were defined in [[air traffic control]] (ATC) and [[secondary surveillance radar]] (SSR) in 1960.<!-- source needed! -->

{{anchor|Gillham}}The code is named after Ronald Lionel Gillham, a signals officer at Air Navigational Services, [[Ministry of Transport and Civil Aviation (United Kingdom)|Ministry of Transport and Civil Aviation]], who had been appointed a civil member of the [[Most Excellent Order of the British Empire]] (MBE)<!-- unclear if this was related to his involvement with this code, or for some other achievements --> in the Queen's [[1955 Birthday Honours]].<ref name="LG_1955-06-03"/> He was the UK's representative to the [[International Air Transport Association]] (IATA) committee developing the specification for the second generation of air traffic control system, known in the UK as "Plan Ahead", and is said to have had the idea of using a modified Gray code.<!-- while having a family dinner. --><!-- Reportedly he "suddenly" died in March 1968. --> The final code variant was developed in late 1961<ref name="Ashley_1961"/> for the ICAO Communications Division meeting (VII COM) held in January/February 1962.,<ref name="IEEE_1983"/> and described in an [[FAA]] report later this year.<ref name="FAA_1962"/><ref name="FAA_1962_T6"/><ref name="FI_1964"/> The exact timeframe and circumstances of the term ''Gillham code'' being coined are unclear, but by 19621963<!-- not a specific date, just the earliest source using the term I could find so far. --> the code was already recognized under this name<ref name="CS_1962"/><ref name="CE_1963"/> and described in an [[FAA]] report.<ref name="FAA_1962CS_1963"/><ref name="FAA_1962_T6"/><ref name="FI_1964CE_1963"/> By the mid-1960s the code was also known as ''MOA–Gillham code''<ref name="Wheeler_1969"/> or ''ICAO–Gillham code''. ''ARINC 572'' specified the code as well in 1968.<ref name="ARINC_572"/><ref name="ARINC_572-1"/>

Once recommended by the [[ICAO]] for automatic height transmission for air traffic control purposes,<ref name="FI_1964"/><ref name="Wightman_2017"/> it is now discouraged<ref name="Tooley-Wyatt_2009"/> and has been mostly replaced by modern serial communication in newer aircraft.

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<ref name="Decoder Patent">{{cite patent |title=United States Patent US3805041 - Circuit for converting one code into another code |inventor-first=Hans |inventor-last=Langheinrich |assignee=[[VDO Tachometer Werke Adolf Schindling GmbH]] |fdate=1971-10-27 |adate=1974-04-16 |id=Application 192830 patent 3805041 |url=http://www.freepatentsonline.com/3805041.pdf |access-date=2018-01-14 |url-status=live |archive-url=https://web.archive.org/web/20200518095507/http://www.freepatentsonline.com/3805041.pdf |archive-date=2020-05-18}} (7 pages)</ref>

<ref name="Stewart_2010">{{cite web |title=Aviation Gray Code: Gillham Code Explained |date=2010-12-03 |author-first=K. |author-last=Stewart |publisher=Custom Computer Services (CCS) |url=http://www.ccsinfo.com/forum/viewtopic.php?p=140960#140960 |access-date=2018-01-14 |url-status=live |archive-url=https://web.archive.org/web/20180116184525/http://www.ccsinfo.com/forum/viewtopic.php?p=140960 |archive-date=2018-01-16}}</ref>

<ref name="CS_1962CS_1963"><!-- TBD: It is important to find out the exact volume/year and issue number in order to find out if the term "Gillham code" was already used in 1962, or only in 1963. -->{{cite journal |title=Beacon Encoder |journal=Computer Design (cd) |publisher=Computer Design Publishing Corporation |date=<!-- May or September? -->1962–1963 |volume=1 or 2 |number=<!-- 5 or 9? --> |issn=0010-4566 |oclc=802774218 |publication-place=Massachusetts, USA |page=45 |url=https://books.google.com/books?id=npg_AQAAIAAJ |access-date=2018-01-16 |quote=[…] Output code of a new Beacon encoder is known as the Gillham code, a modified [[Gray code]] designed to be compatible with both American and European traffic systems. […]}}</ref>

<ref name="CE_1963">{{cite journal |title=New Products |journal=Control Engineering (CtE) |issn=0010-8049 |publisher=Technical Publishing Company |date=January–December 1963 |volume=10 |issue= |id=(344) or (345) |page=110<!-- of which monthly issue? --> |url=https://books.google.com/books?id=DPpIAQAAIAAJ |access-date=2018-01-16 |quote=[…] Designed to be compatible with American and European traffic systems, a beacon encoder available from Norden Div., United Aircraft Corp., Norwalk, Conn., puts out a modified [[Gray code]] known as the Gillham code. […]}} [https://books.google.com/books?id=xkASAAAAIAAJ]</ref>

<ref name="ARINC_572">{{cite book |title=Mark 2 Subsonic Air Data System |id=ARINC 572 |date=1968-02-15 |page=55 |publisher=[[Aeronautical Radio, Incorporated]] ([[ARINC]]) |___location=Annapolis, Maryland, USA}}</ref>