‘Squawk’ is a throwback from when the equipment (transponder) was known as the ‘Parrot’ because it just repeats the code ‘Parrot’ fashion.
In real terms there are basically 2 types of air traffic radar, Primary radar sweeps an area (around 6 seconds for a full 360 degrees) and sends out a signal that returns by bouncing off your aircraft, the radar knows its direction and the time taken for the signal to return which gives your direction and range but not altitude.
Secondary radar uses the specific code you’ve been allocated (your squawk) to receive the signal from your aircraft which identifies you as that return, combined with your altitude from the read out on your transponder.
Combining the 2 will give position and altitude and enable the controller to give separation between ‘contacts’
‘Squawk Ident’ means the controller is asking you to momentarily press and release the IDENT button which will cause your tag on the ATC radar display to increase brightness or be highlighted for a short period of time to stand out from all the other symbols on the display.
ATC will have a list of codes for their use so with practice you get used to what codes you’ll be asked to squawk along a regular route.
I was lucky when flying police that the aircraft had an allocated squawk that didn’t change and just showed the Police callsign on the radar, so that ATC could see us coming before we even arrived on frequency.
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