Timeline for Is "secondary radar" a misnomer?
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
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| Feb 2, 2020 at 6:13 | vote | accept | RoboKaren | ||
| Oct 3, 2018 at 12:20 | comment | added | boxtrain | @mongo Those terms are switched. Primary Surveillance Radar is an active radar system - bounces signals off of aircraft and listens to the reflection. Passive radar listens to reflections from an unintentional source (eg radio towers). Secondary Surveillance Radar isn't quite either (sort of active because it sends out its own signal, but doesn't use actual reflections). | |
| Apr 16, 2017 at 2:57 | comment | added | mongo | Without going through the history, better terminology would be the primary is a passive system, relying on a reflected return from the aircraft. The secondary system is an active system, which broadcasts a reply in response to an interrogation. Azimuth and time of "flight" are used to determine the location of the transponder responding to the interrogation. Newer secondary modes do not require an interrogator and self-report location. Probably not really secondary radar, but the function is similar. All three methods are independent. | |
| Mar 7, 2015 at 18:11 | comment | added | RoboKaren | So I don't know the "real" answer to this so I'm not sure which of the answers to select. Tyler's seems just as good as Greg's -- but don't know why there is currently a 9:1 in favor of Greg's. Is this because Greg is more correct (why?) or simply because he was the first to post? Advice on which to select is appreciated. | |
| Mar 7, 2015 at 8:01 | comment | added | reirab | @cpast is correct. Only the altitude and 'squawk' code are encoded in the response (in Mode C, at least... a bit more goes into Mode S responses, IIRC.) In addition to timing, though, actual antenna response differences are measured to help determine bearing more precisely than could be done with timing alone. The timing could be faked (by delaying the response,) but faking antenna response differences would be really hard to pull off reliably. | |
| Mar 6, 2015 at 17:57 | comment | added | cpast | SSR doesn't ask the plane for its position, though; it computes distance and azimuth from timing, just like primary radar. | |
| Mar 6, 2015 at 15:19 | answer | added | Tyler Durden | timeline score: 3 | |
| Mar 6, 2015 at 3:27 | history | tweeted | twitter.com/#!/StackAviation/status/573686208485785600 | ||
| Mar 6, 2015 at 1:04 | answer | added | Greg Hewgill | timeline score: 12 | |
| Mar 6, 2015 at 0:14 | history | edited | RoboKaren | CC BY-SA 3.0 |
edited title
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| Mar 6, 2015 at 0:02 | comment | added | RoboKaren | Yeah, but by that definition the ATC contacting the plane by radio and verbally asking the pilot for a GPS position readout would also be radar. Which is essentially what SSR is, but automated (and not as detailed). | |
| Mar 6, 2015 at 0:00 | comment | added | cpast | It still uses radio waves to detect aircraft and find the distance to them, right? | |
| Mar 5, 2015 at 23:38 | history | asked | RoboKaren | CC BY-SA 3.0 |