Everyone knows the radio communications doesnt sound great altough they work perfectly.

But can the brand new ADS-B communications be used for carrying audio signal? Would it be clearer?

The ADS-B will be mandatory by 2020 (At least for anyone that wants to fly at the controlled airspaces) so why dont we ditch the old radio system full of parasties and use ADS-B instead for voice communications instead?


Why dont we ditch the old radio system full of parasties and use ADS-B instead for voice communications instead?

Well, why don't we use televisions for washing dishes? Because televisions don't wash dishes.

Likewise, ADS-B doesn't carry an audio signal, so it can't be used for voice communications.

Perhaps ADS-B could be modified to carry voice signals, but this is probably not a good idea. The reason for this is that, while aviation voice communications currently use a band which is 19 MHz wide, the band that ADS-B uses is only about 1 MHz. (The Signal Identification Guide says, "There are two types of ADS-B: one [...] with about 50 kHz of bandwidth; [and] one that transmits at 978 MHz [...] using a larger bandwidth of about 1.3 MHz".)

Transmitting voice signals digitally is a good idea, but I don't know of any reason why this would be done using ADS-B. It would make more sense to simply design a new protocol from scratch.

  • $\begingroup$ It appears that you are mixing up service bandwidth and channel bandwidth. VHF airband channel bandwidth for voice is usually 6, 8 or 25 kHz. 19 MHz is the combined bandwidth for 760 channels. ADS-B has a channel bandwidth of either 50 kHz or 1.3 MHz. The latter would be sufficient to transmit high quality surround sound. $\endgroup$ – bogl Nov 15 '19 at 13:52
  • $\begingroup$ @bogl Maybe I am. We have a total of 19 MHz of the radio spectrum allocated to aviation voice communications, and I interpreted the linked wiki page as meaning that there's a total of about 1.3 MHz allocated to the 978 MHz band of ADS-B. Maybe I interpreted that wrong, though. I'm also not entirely sure what point I was trying to make with the bandwidths in the first place, come to think of it. $\endgroup$ – Terran Swett Nov 15 '19 at 14:01

ADS-B is very low bandwidth and is completely unsuitable for carrying voice traffic. The answer to the "why don't we" question is quite simply "it doesn't work that way".

  • $\begingroup$ Alternatively, text messages are noise-free. $\endgroup$ – ymb1 Jun 19 '19 at 0:16
  • $\begingroup$ Please see my comment on Terran's answer. $\endgroup$ – bogl Nov 15 '19 at 13:52

As an additional point... the reason ADS was given its own frequencies was so that other communications would not interfere with the needed Position and Identification information sent out via that method. ADS can in many places surplant the need (though I'm not at all suggesting that it should do so) for primary radar. There are too many things that can end up in the air that primary radar can see which don't have a any transmitters...flocks of birds come to mind, planes with malfunctioning radios, weather balloons or even idiots in lawn chairs with balloons.

By nature -- in radio -- a single station is either listening or transmitting if you have ATC transmitting on that frequency, 3 things will happen.

  1. ATC wont hear all of the other stations transmitting on the frequency,

  2. Any other Receiver wont hear anything except ATC's extremely powerful transmitter attached to good antenna.

  3. Since ATC is stationary on the ground its position, altitude, and all of the other things reported in a ADS packet will be particularly useless to all of the other planes that can also receive ADS traffic.

The last factor is Time all of those ADS identifiers are really really short in time -- way under a second. This is why so many planes can use the same frequency.

Even if two stations step on each other, transmissions have a random delay between them from a given station. Good signal processing can even separate stations that transmit at the same time in some conditions, for instance if each transmitter is slightly off the center frequency differently.


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