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I have a few questions on the radio comms. aspects of commercial aircrafts.

At what (central) frequency does an aircraft communicate with a control tower? Is the communication over one frequency only? How much is the transmit power of the antenna per channel on both uplink and downlink? Is it per hertz?

Also please correct me if I’m wrong: From my readings, aircraft-airport communications is analog only, correct?

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  • $\begingroup$ This seems very similar to your previous question $\endgroup$ – Pondlife May 9 '18 at 1:49
  • $\begingroup$ Just to be clear, in the elevated structure that enables those in it to see over, usually, the rest of the airport buildings, there are, typically, two ATC positions manned by different people: the 'tower controller' and the 'ground controller', and they use different frequencies. At larger airports there might also be discrete frequencies for 'clearance delivery' and 'ramp control' as well as others. When you speak of the 'tower' are you referring to the 'tower controller' or the aggregate of the controllers in the physical structure known as the tower? $\endgroup$ – Terry May 9 '18 at 3:41
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In the US, non-military Aviation uses VHF frequencies from 118.00 MHz to 136.990 MHz in both 8.33kHz and 25 kHz spacing. Generally, one radio is used for one frequency at a time. With 2 pilots, 2 radios on 2 different frequencies can be used together; for example one listening/talking to approach, or a control tower, while the 2nd listens to ATIS/ASOS for airport information.

Perhaps the big iron can do 2 frequencies at once in 1 radio unit.

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At what (central) frequency does an aircraft communicate with a control tower?

This is different for every tower, although due to the limited discrete frequencies around the globe they are repeated, generally far enough apart its not an issue. Specific frequencies can be found for US airports on either charts or in the AFD.

Is the communication over one frequency only?

Generally every tower only has a single frequency, there are some airports or enough traffic to warrant multiple frequencies. They are often segmented by approach direction or runway.

How much is the transmit power of the antenna? Is it per hertz?

Transmit power may vary based on airport but should be constant across the frequencies.

Also please correct me if I’m wrong: From my readings, aircraft-airport communications is analog only, correct?

Not analog only, digital comms are used. For the airport environment there are systems such as CPDLC for delivery clearances and D-ATIS for digital airport information.

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  • $\begingroup$ Could you please give a typical range of transmit power? Also, if the transmission is over one frequency, then why did you say ‘channels’? Cause each channel correspond to a different frequency to me. $\endgroup$ – Teodorism May 9 '18 at 2:09
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    $\begingroup$ Many towers will transmit simultaneously on a VHF and a UHF frequency. Some military aircraft only have UHF radios, so when the controller keys the mic, he's transmitting on both radios at once, so everybody tuned to the appropriate tower frequency (on either band) will hear him. $\endgroup$ – Ralph J May 9 '18 at 2:44
  • $\begingroup$ Is the aircraft transmit power the same as the tower? $\endgroup$ – Teodorism May 9 '18 at 3:39
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    $\begingroup$ @Teodorism it depends on what the airplane is equipped with, the plane I fly has a 10W radio while a 737 has a 400W HF and 25W VHF radio $\endgroup$ – Dave May 9 '18 at 4:02
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    $\begingroup$ @Teodorism these would be good topics for new questions. $\endgroup$ – fooot May 9 '18 at 15:05

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