Talk:Secondary surveillance radar

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There needs to be an explicit mention of "IFF" since that redirects here. --Askari Mark | Talk 02:08, 5 September 2006 (UTC)

Go ahead and add one. It mentions military several times in the article. I think IFF is just military secondary radar. Dual Freq 03:12, 5 September 2006 (UTC)

Okay, not my area of expertise really, but I think what I added does the job. :-) --Askari Mark | Talk 19:06, 5 September 2006 (UTC)

The article doesn't mention this but it should be noted that military vessels also use IFF and are not only equipped with interrogators, but also transponders.

When was IFF invented?[edit]

The article says "during the second world war" but it was in use during the Battle of Britain, so either it was developed in the short period between the start of the war and that battle, or it was developed before the war. Does anyone know for certain? Man with two legs 11:02, 20 February 2007 (UTC)

I do not have references to printed sources for this, but there are web sources that I think could be regarded as reliable (please excuse the following bare links, but they seem appropriate in this context). The web site of the US Naval Research Laboratory claims that NRL developed an electronic aircraft identification system in 1937 (see It does not provide any helpful details but other sources seem to be agreed that the first challenge/response system, which could be reasonably regarded as the beginning of modern IFF, was developed after the beginning of the war in response to the special challenges of the time. The home page of the US 551st and 552nd AEW Wings, at, states that an active challenge and response identification system was developed after 1940. See also, which agrees. An archive section of the Institution of Engineering and Technology's web site contains a facsimile of the first page of a report by Hazeltine, dated 1947, describing a challenge/response identification system, which it actually calls 'Identification Friend or Foe'.
I hope this helps. Trog23 14:10, 20 February 2007 (UTC)
Thanks. That suggests that IFF was indeed invented shortly after the war started. Man with two legs 16:32, 20 February 2007 (UTC)
IFF was devised by the British (who also invented the term) as part of the Chain Home system, well prior to World War II. It was realised by Robert Watson-Watt and his team that friendly aircraft appearing on RDF (as radar was then called) would need to be identified from possibly enemy ones. The early form was known by the codename Pipsqeak, which was non-automatic and required the pilot to activate it when requested by radio from the ground controller. Later versions incorporated a proper automatic transponder. Ian Dunster 11:43, 9 March 2007 (UTC)
Ian - thanks for the contribution. If my understanding is correct, Pipsqueak was a system that 'hijacked' an aircraft's VHF voice comms radio to transmit a 1kHz tone on a frequency used by DF (direction finder) stations and thereby allowed the aircraft's position to be triangulated by ground staff. It was indeed intended to identify friends and distinguish them from foes, but did not operate on radar (RDF) frequencies and was not integrated with the radar. The first system designed to operate with the Chain Home RDF system was a passive, tuned antenna that caused a stronger response from the equipped aircraft. This was quickly replaced by an active transmitter called IFF Mk1, which was more effective but still only generated a response to RDF transmissions, similar to simple reflections but stronger; its replies contained no coded information from the target. So far as I can tell, the first challenge-response system that permitted any exchange of information between the ground station and the target, similar to modern IFF, was not developed until after the Battle of Britain. This I believe came with what was designated IFF Mk3, although I don't know exactly when it was introduced. I guess the issue here is what should we consider to be the true origin of IFF. I had considered it to be the first challenge-response system with a coded reply (IFF Mk3), but I will be happy to be 're-calibrated'. Any offers, anyone? Trog23 18:56, 13 March 2007 (UTC)
My pleasure - I seem to remember reading that one version of IFF momentarily increased the brightness of the blip on the RDF screen when interrogated, but unfortunately I can't remember any more. Ian Dunster 21:50, 15 March 2007 (UTC)
Just found this here: ORIGINS OF IFF Ian Dunster 20:28, 20 March 2007 (UTC)
Ian - thanks, a good find! I enjoyed reading that - a well written article that is consistent with other information that I have been able to find and appears reliable. So the origin of the term 'IFF' certainly seems to pre-date the second world war (and can be attributed to us Brits), although coded replies from the target did not arive, so far as I can tell, until after the Battle of Britain. On reading through again, the Article page here seems to contain appropriate information although I guess that your new reference should be of great interest to the Miltiary History people (iaw box at the top of this page). Regards Trog23 15:22, 21 March 2007 (UTC)
My understanding is that IFF resulted from the Battle of Barking Creek which took place on the 6th September 1939, three days after the war started. Aircraft were detected by radar and fighters were sent to intercept and shot some down only to find that they were on our own side. The first IFF detected the primary radar transmiussion and enhanced the echo so that the ground radar could see that they were friendly. These were IFF Mk I and Mk II. However with different types of radar being developed, particularly those transmitting on a higher frequency, it became impractical match each airborne IFF equipment to each ground radar and IFF Mk III was developed which responded to a separate signal in the 157-187 MHz band. I think that I read this in either Swords, S. S. Technical History of the Beginnings of Radar, Peter Peregrinus, Stevenage, 1986 or in Lord Bowden of Chesterfield. The story of IFF, Proc. Inst. Electr. Eng. Part A,132(6), 435-437, 1986. But I do not now have access to either to check. Michael Monopulse01 (talk) 15:37, 31 December 2010 (UTC)

IFF history request[edit]

Since IFF currently redirects here, there should be a section on its history included in the article, until a separate article can be prepared. This is out of my field, but it is an obvious gap in coverage unless it is already in some other Wikipedia article. A check of the article history shows that this article used to be titled Identification friend or foe, and a version from June 2006 indeed has more historical information that has since been eliminated. --Blainster 17:58, 24 February 2007 (UTC)

Additional Resources[edit]

US Navy publications: Operations Specialist Volume 01 chapter 8 and Electronics Technician Volume 4-Radar Systems chapter 3 both talk about IFF and SSR. They are public domain documents that the USN released. The links I put here are from tpub, they digitized them, but the information is still public domain. Might be some information in there to add add to this article, I don't have time at the moment, but maybe they will be useful to someone else. Dual Freq 22:25, 8 September 2006 (UTC)

Possible copyvio removed see also: [1] --Dual Freq 23:18, 2 January 2007 (UTC)


I would like to suggest improvements to the overview:

First para third sentence implies that PSR is synonymous with ATC, whereas it is just one of several technologies that support the service - SSR is another.

Second para final sentence implies information is exchanged between the ground PSR and aircraft SSR - in fact it is between the ground SSR interrogator and the aircraft's SSR transponder (terms that are used later in the article and could be introduced helpfully in the introduction).

If you agree, I will attempt changes (as a newbie here I don't want to interfere without first introducing myself). Trog23 06:07, 13 February 2007 (UTC)

Welcome, and don't be afraid to be bold! Edits to correct or clarify are always welcome. If someone disagrees and reverts an edit of yours, simply post a new topic on the Talk (Discussion) page to work it out. You'll find that many articles begin as stubs and accrete more detail in bits and pieces over time — unless someone "adopts" the article and works it to comprehensively improve it. The Talk pages also often have a box at the top of the page informing you of what Wikipedia:WikiProject(s) are interested in the article and these are great places to learn what particular style standards they apply to articles they're involved with. Their Talk pages are a great place for asking questions. If you have any questions I can help with, please post them on my User Talk page. Askari Mark (Talk) 15:40, 13 February 2007 (UTC)
OK - thanks. I have expanded the introductory paragraph, tidied up the ambiguities in the overview and made minor changes at the beginning of the 'Operation' section (a primary radar target can be displayed with a 'tag', but with more limited information). I have tried to do my homework with the guidelines but there is rather a lot there to get my head around so apologies in advance for any blunders. Trog23 07:31, 18 February 2007 (UTC)

Separate IFF Article[edit]

Identification Friend or Foe systems take many forms, and an IFF transponder is only one type. To lump IFF in with Secondary Surveillance Radar is inaccurate, as the IFF hardware used on fighting vehicles is completely ignored, to say nothing of less technological forms of IFF. To properly cover the types and details involved in the myriad Identification Friend or Foe systems used worldwide, IFF should be broken out into its own article. —The preceding unsigned comment was added by (talk) 15:15, 4 May 2007 (UTC).


I personally disagree with some statements in the article, namely that IFF has multiple incarnations. IFF as used by the military is only a basic form of IFF and is even less accurate for civilian craft. IFF in its true form is much more complicated and still HASN'T been made yet. The true form of IFF is still MANY years from being perfected, as the basis of the system is to identify enemy or allied craft WITHOUT using radio signals or fixed ground installations.

Proposed merger[edit]

This is rather silly that we have two articles differing only by case (Article 1: Identification_friend_or_foe, Article 2: Identification_Friend_or_Foe) with related content. It is confusing to say the least and so I am proposing that we merge them, or if their differences are irreconcilable, then that we at least change the name.- 05:56, 4 July 2007 (UTC)

Uh, no. I suggest merging in the opposite direction. IFF is SSR with mode 4 added. Both articles used to redirect here and still should. Identification Friend or Foe redirects here and is not an article. --Dual Freq 12:38, 4 July 2007 (UTC)
I'm with Dual. IFF should redirect to the IFF page. Kevin 02:58, 9 July 2007 (UTC)
My apologies, that is not what I meant. What I was trying to say is that Identification Friend or Foe and Identification friend or foe should both redirect to this article, Secondary surveillance radar. The only difference is the additional modes used by the military, and that is covered in this article's modes section. All other modes appear to be the same, at least in US systems. --Dual Freq 03:21, 9 July 2007 (UTC)
Since when is IFF a military-exclusive term? —Preceding unsigned comment added by (talk) 15:03, August 27, 2007 (UTC)


there is a merge discussion tag on Secondary surveillance radar. Is this in error? I would oppose merging IFoF into SSR, unless there is a danger of overlap in the articles. — Xiutwel ♫☺♥♪ (talk) 19:42, 8 August 2007 (UTC)

Proposed Merger of Transponder (aviation) with Secondary surveillance radar[edit]

This article was tagged for consideration for merger on 11 December 2007 by PEHowland. The tag was incorrectly constructed and led to the wrong talk page, so that may have slowed down comment on this issue!

I have started the debate on this proposed merger on the Talk:Transponder (aviation) page. - Ahunt (talk) 23:25, 1 January 2008 (UTC)

Citation needed[edit]

Is someone inserting [citation needed] at the end of every paragraph and at the individual contents of many of the tables? If so could they please explain the problem.Monopulse01 (talk) 12:55, 15 January 2011 (UTC)

Yes I did, as we discussed on your talk page. As explained at WP:V all these additions need to be properly cited with footnotes to reliable references or else eventually they will be removed. - Ahunt (talk) 13:50, 15 January 2011 (UTC)
Okay I have fixed a bunch of formatting errors and the removal of a number of "citation needed" tags where no refs were provided, the run-down is in the edit summary for each change. - Ahunt (talk) 19:53, 15 January 2011 (UTC)

Mode S[edit]

Beware with the "Mode S interrogation, short and long" image. It is wrong and lead to misinformation! Preamble doesn't last 30.5µs, but 3.5µs.

See as a clarification.

P1 to P6 its clearly impossible to be 30.5µs!

Please, see page 3-82 from ICAO, Annex 10, Volume IV, Surveillance and Collision Avoidance Systems. I don't know if images from that document could be reproduced here without permission.

More details on the picture discussion page Rapid2k1 (talk) 21:19, 30 October 2011 (UTC)

You probably need to take this up with User:Monopulse01 as it is his image and also his text that goes with it. - Ahunt (talk) 22:27, 30 October 2011 (UTC)


Since the IFF article is now separate, this article needs to be reviewed for more appropriate projects. Because of the referral to SSR as based on IFF, it's appropriate to retain WP:MILHIST. I've added aviation without assessment but there may be other technology projects I'm not familiar with. --Lineagegeek (talk) 22:01, 15 February 2014 (UTC)

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