ping ping pong

[spinner2]

I put a transponder in my Cub. It didn't have one before. It is a Becker with an encoder and I noticed shortly after leaving our airport today that it was sending out replies. With the Becker a triangle icon flashes when its making a reply and this started well before I was high enough to be seen by radar. We're in a small valley surrounded by mountains and have to climb 4000' or so above the valley to be seen.

So I'm wondering who was interrogating my transponder at low elevations? Will Tecas in an airliner do it? I'm about 100 miles south of the border and wondered if an Awacs was high overhead sniffing around? I flew high enough and far enough north later that I knew Salt Lake Center could see me and I tuned in Center frequency and heard some airliners overhead.

In the Cessna I never pay attention to the transponder (a Narco) and am usually going up and over to a destination so haven't seen this in that plane. In the Cub though today I was low and slow in a couple of valleys looking at game. And I saw my first wolf of the new year. He was a bold fellow trotting on up a road unconcerned as I made several passes overhead at 200'.

Any idea who's pinging the transponder?

 

[jmkota]

A TCAS equipped airplane will cause your transponder to transmit. You were right.

 

[Ruidoso Ron]

I have found that my strobe lights will cause the reply light to flash on my KT76A. Don't know if it is actually replying, or not. Probably due to inadequate shielding somewhere.

 

[StewartB]

My transponder response light blinks while on the ground in some pretty remote places. I assumed it was just programmed to transmit occasionally. On the topic of TCAS, does a TCAS query transponders within range or simply identify transponders that are transmitting? I thought TCAS units were receivers, not transmitters. Transponders are transmitters, aren't they?

SB

 

[jmkota]

I don't know all the details of how a transponder/TCAS works, but I do know that TCAS sends out a signal that makes transponders reply. This way, even in the middle of an ocean crossing, if an airplane is at your alt, TCAS will work. I don't know about TCAD, but systems like the Zaon XRX do not transmit and therefore will not work if no one else causes the intruding airplane's xpnder to reply. A lot of the time, during normal traffic down south here, there are ample radars and TCAS equipped airplanes to make these passive systems work, but no guarantees.

There is a lot more to TCAS than just recieving - two TCASs will talk to each other somehow, so that both don't tell the pilot to pull up at the same time and things like that.

Thats how I understand it.....

Jack