I also thought that a 75 76 or 7700 sqwark remained on the radar screen even if you change sqwarks afterwards. Although ATC Babes post sugest otherwise. Can anyone clarify?
Depends on the transponder fit. Some models have an "Emerg" function will will transmit 7700 as well as the assigned code. It is these that will keep the code / callsign displayed as well as the emergency. For the majority of us though it's a case of you display what you select - if you deselect 7700 then it doesn't show anymore.
I believe (but stand to be corrected), that radar antennae sweep every 10 seconds, so presumably if one changed the transponder code within less than 10 seconds, the changing code would not show up on the radar screen. Would this not explain the delay that has been mentioned?
1) How do you know what part of the sweep you were in and 2) You are not being interrogated by one SSR, but possibly by several at different times - why do you think the interrogation light blinks irregularly. It's true the average scan rate is 10 seconds - some may be slightly faster, some may be slower.
CM