Squawk Ident

[2lo4zero]

Help needed to ATC techie type! :)

When asked by ATC to squawk xxxx with ident do you hit the ident tit and then dial up the new numbers?

Reason I ask is that we are getting some problems with code/callsign pairings which we suspect may be down to the new squawk code being suppressed on interrogation whilst the ident feature is in operation. What happens is that the radar data processing software is alerted by an ident and tries to match up the code observed with the codes allocated by it and then pairs it to the callsign which has that code allocated. However the effect we see occasionally is that the wrong callsign (and associated flight data) is paired, which we suspect is the radar data processor observing the old squawk. This is because the processor waits for 3 radar illuminations of the target, a time interval of 12 seconds (illuminate, 6 second sweep, illuminate, 6 second sweep, illuminate). As (we believe) the ident pulse operates for 20 seconds which would be more than long enough to cause the wrong pairings.

Thanks
2lo

[Tinstaafl]

Select the code then press 'Ident'. No particular delay between the two but always in that order.


Edited to add I took it as read that the TXDR is switched to STBY prior to code selection.

[Sheep Guts]

oK ZERO,
Most transponders have a code select knob seperate and an Ident button and also a 4 position switch labeled OFF , STDBY, ON, ALT.

Some Students or Pilots who havent been instructed in the correct use, may switch the code select without turning the unit to standby or off first. If this isnt done, spurious codes are transmitted by the unit, as the Code Select Knobs are dialed, upsetting the gear at your end and what ATC see. This is a common stuff up.

This may account for this effect you are seeing.

Regards
Sheep

As tin has said select the code (ensuring its in stdby or off mode) switch back to ON or ALT ,then hit the ident button.

[Ttree Ttrimmer]

Sheep Guts,

The transponder on my type does not require that the unit be switched to stby for a code change. When a squawk change is initiated the old code is held by the transponer until after the numbers have been set (3 seconds I believe). What may be happening is that the numbers are being set then ident pressed and the box is still using the old squawk as it is within the hold over period.

Interesting point though and one I will consider next time I am asked to change the code and ident.