John posted, in part:

Can someone tell me what this is and what it does?


IFF is Identification, Friend or Foe. You have the airborn end of the system.

In early systems, which I believe is where this would be, age-wise, that
transponder would automatically transmit a signal in response to having
received an "Interogation," aka "Challenge" from a radar station. There were
only three possible responses to an interogation: 1,2, or 3 blips. These
would be seen on the Radar Station "B" scope next to the echo return signal of
the radar. That's the one with the circular trace.

Each day a different one of the three codes would be assigned.

An aircraft that sent no IFF signal or a wrong one, would be assumed
unfriendly.

As late as the 60s this type of IFF was in use. I was once a civilian
employee/operator at an operational RADAR station. The secret IFF code of the
day was not given to us. We tracked aircraft and gave the grid coordinates and
IFF status to the Airforce on special lines. They decided if it was friend or
foe.

It seems silly now, but at the time it was serious stuff to report "I have a
bogey on my gadget and the parrot's sqawking 1" or 2 or 3.

Don