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I don’t think ATC currently has the capability of seeing who’s actually transmitting on the frequency.

If technology permits (probably by making a connection between the radios and the transponder), would it be helpful for controllers to be able to know the actual aircraft that’s transmitting on the frequency through their radar?

Does it also have the possibility of eliminating the requirement of saying the callsign after each transmission (might help in extremely busy airspaces)?

The visual aspect would be similar to how the “ident” feature works (like seeing a little “TX” when someone is transmitting).

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    $\begingroup$ Possible duplicate of Is Ground Direction Finding commonly used? $\endgroup$
    – user14897
    Jun 3, 2018 at 1:36
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    $\begingroup$ There seem to be two questions here. The title asks whether it's possible, while the body says you don't think it's possible but asks whether it would be helpful. $\endgroup$
    – Zach Lipton
    Jun 3, 2018 at 5:18
  • $\begingroup$ This question also lacks a region or country- capability differs accordindly. $\endgroup$
    – jwzumwalt
    May 7, 2019 at 15:37
  • $\begingroup$ What real world problem is this going to solve? If the callsign isn't used, how will those listeners without radar identify them? Radio communications is helpful for other aircraft maintain situational awareness. $\endgroup$
    – Steve Kuo
    May 9, 2019 at 5:04

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A version of this has been implemented in some areas, such as the Maastricht Upper Area Control Centre, using radio direction finding equipment.

The EUROCONTROL website provides an explanation of the system, including an image of how it appears on radar displays:

Using triangulation software, the Radio Direction Finder, recently deployed throughout MUAC’s international airspace (the upper airspace of Belgium, the Netherlands, Luxembourg and north-west Germany) calculates accurately an aircraft’s position on the basis of its radio transmissions.

In densely occupied airspace, the Radio Direction Finder assists the controllers in rapidly identifying which aircraft is transmitting on the frequency. This is particularly useful in MUAC’s sectors where controllers handle up to 25 aircraft at any one time, and is a prerequisite for the implementation of the free route airspace, planned at the end of the year. The origin of a voice transmission appears clearly on the controller’s integrated Human Machine Interface and is totally independent of conventional radar- and GPS-based aircraft localising techniques; this feature contributes to reducing call sign confusion, read-backs from wrong aircraft or crossed transmissions.

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As you state correctly, they can’t see who is transmitting. Despite that the functionality is not build into the radios currently installed in thousands of planes, that would also mean you would have to register a hand radio a specific plane.

In theory you could use analog technology to transmit short data pieces with every PTT. There is a good reason why aviation is still analog though. Analoge signals can still be understand, even if connection is really bad. It will be a lot more noisy and the pilot might not be understandable crystal clear, but the message will arrive. While in a digital environment you will get what you have on your mobile.

If you take bad connections in consideration, you would need to send the data signal several times to be correct and display the right call sign. That would probably take more time and block the frequency.

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    $\begingroup$ In amateur radio, and some other uses, there is CTCSS for, IIRC, Continuous Tone-Coded Squelch System. It uses low-frequency tones (below about 250 Hz) to allow a receiver to open the squelch only when a "valid" signal is being received. I don't think it sees much use outside FM, but I don't see why a similar system couldn't be used with AM. Reserve a couple of low-frequency tones and they could be notched out in the LF or AF stages without significantly impairing human understanding. From there, simple AFSK could be used to transmit short bursts of data such as a 24-bit mode-S transponder ID. $\endgroup$
    – user
    Jun 3, 2018 at 12:51
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Mostly No, as normally configured. Slow traffic or particular positions may be identified by ATC listening on two radios simultaneously i. e. a BUEC, RCAG or portable radios especially, could identify how far away you are by precisely setting the squelch on a PET-2000 or other portable radio. The antennas for such facilities are at different locations which affects where transmitted signals will be received. It would be fairly easy with slow traffic and particular locations given multiple or lengthy transmissions.

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Military transponders had, or possibly still have, a switch that, if selected, will cause an IDENT during every radio transmission. This would have been very useful on radar displays with no target datablocks.

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  • $\begingroup$ This is true, at least up until 2006. I can't remember the name of the switch position, (I never used it) but that is exactly what it did. $\endgroup$
    – Michael Hall
    May 7, 2019 at 15:45
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As David pointed out, they do not have any way to know where or who you are by com radio.

In the United States the FSS use to have directional steering capability for lost airplanes (and be able to locate the aircraft transmitting), but even that was done away with outside Alaska in 2007, then in Alaska in 2013. You would ask for a "directional steer" and they would ask estimated ground speed and would have you do a couple turns over a 3-5min period to identify your location by triangulation.

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  • $\begingroup$ This is just wrong! Using VDF you can! Check Zachs answer $\endgroup$
    – pcfreakxx
    May 7, 2019 at 10:40
  • $\begingroup$ @pcfreakxx - Because this question lacks a region or country- capability differs accordingly. My answer is correct for the the United States (which it clearly stipulated). There is no longer VDF in the US. $\endgroup$
    – jwzumwalt
    May 31, 2019 at 17:39

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