Well, since I never heard back from Trig, here's what they told me about
pressing the IDENT button:

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Pressing the "IDENT" button sets a flag in the transponders Mode A and
Mode S replies for 18 seconds to allow ATC to identify you quickly
(*Note: not Mode C replies, as this is just altitude data). It does not
force the transponder to transmit and it will still need to be
interrogated in some way either by TCAS or a ground SSR. However, the
Trig TT22 also sends out Mode S Squitter transmissions independent of
any interrogation. The squitter contains acquisition data and is
broadcast approximately twice a second, this acquisition data also
includes the IDENT flag.

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"JJ Sinclair" wrote in message
...
On Jan 20, 7:43 am, "Dan Marotta" wrote:
Having installed a Trig TT22 in my LAK-17a, I've noted that, when I press
the IDENT button, the reply indicator turns on for some finite time which
is
longer than a normal reply to an interrogation. Since I know absolutely
nothing about transponder protocol, I sent a message to Trig's tech
support
and got a very detailed reply about how it works.

Not wanting to step on any toes (unusual for me, huh?), I replied to Andy
at
Trig thanking him for the information and requesting permission to post
his
reply. If he says, "Yes", I'll post it here.

In the mean time, Steve's info sounds correct to me.

"Steve Leonard" wrote in message

...
On Jan 20, 3:15 am, GC wrote:



I'd be interested to know how pressing IDENT causes a flag to be set on
the controller's display 100 miles away without any transmission from
the transponder. Telepathy?

GC

As my education continues to rise, allow me to pass along what I think
I have learned. When you press the IDENT button, you tell your
transponder "If I get interrogated in the next X seconds, reply with
this extra bit of information as well." And X seconds is the amount
of time your "reply" light is on after you push the IDENT button.
This additional information that is sent will be received by the
ground station and set a flag to highlight you on the display for the
controller.

Have not personally verified this, but have gotten the same info from
what I consider to be a couple of VERY good sources. So, it is not
done via telepathy, but anticipation. You are asked to IDENT, you do,
and you prepare your transponder for the next interrogation.

See how much we learned this week? :-)

From my Becker 4401-3 manual.
Pressing Ident button (will)............. In mode A and Mode A+C this
triggers the transmission of an identification impulse additional to
the Mode A reply code for approx 18 seconds. During this time "idt"
appears in the bottom line of the LC display.
It says, "triggers the tranmission"
I'm just say'n,
JJ