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Its been over 100 years since we first flew and we still use analog radio with parasites and "radio effect" which changes your sound.

Why don't we ditch the old system and make a mandate a new law where any aircraft that wishes to fly in a controlled airspace has to be equipped with two digital radio communication systems?

What would the coverage costs be like? Doesn't digital systems require less power and antenna size etc to work which would make it better?

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    $\begingroup$ What is the benefit? Just better audio quality? How do you justify the potential billions in implementation costs for that? How do you justify it to the GA community when analog radios cost $2000+, much more for NAV/COM? $\endgroup$ – Ron Beyer Jun 19 '19 at 16:55
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    $\begingroup$ Also for commercial operators, do they have to have 4 radios now? You can't mandate other countries, so an international flight would need both... $\endgroup$ – Ron Beyer Jun 19 '19 at 16:57
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    $\begingroup$ Further would be a problem though since the limited frequencies. I can talk to Minneapolis center from Green Bay, so I don't think that distance is really an issue currently. Local airports don't need the range because they don't need to talk to aircraft they can't control. $\endgroup$ – Ron Beyer Jun 19 '19 at 17:01
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    $\begingroup$ Digital systems can have data corruption as well, so I don't see how going from analog to digital in this case solves an actual issue $\endgroup$ – selectstriker2 Jun 19 '19 at 17:02
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    $\begingroup$ What's the actual issue? I think mose of the "parasites" are just local CTAFs all stepping on each other. Digital radio would be no different. Too many airports too close together, and planes near them transmit and those airborne signals go very far. $\endgroup$ – CrossRoads Jun 19 '19 at 17:08
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Digital is not always better. Digital modes have been created for amateur radio use; the amateur radio VHF 2m band (144–148 MHz) is very similar to the VHF aircraft band (108–137 MHz). I have a radio that uses both FM and a digital mode on the amateur 2m band. Here are some notable differences between FM and digital:

  • When the signals are strong, the sound quality of FM is slightly better because there are no digital artifacts
  • When the signals are weak, digital sounds better because there is no static
  • When the signals are very weak, FM is definitely better because digital either degenerates into unintelligible loud tones ("sounds like R2D2" is what hams say) or is not decoded at all, but analog signals can still be understood with difficulty
  • Only one digital signal should be transmitted at a time on a channel; if two signals are there at the same time, the stronger signal might get through, but more likely neither signal will get through

The reason that old-fashioned AM has been kept for all these years is that if two signals are there at the same time, both signals can be heard and understood (perhaps with difficulty). This is a significant benefit; a quieter signal, perhaps from an aircraft further away from the airport, has a much better chance of breaking through to be heard on a busy frequency. FM and digital modes can't offer that benefit.

Digital radios are not intrinsically more capable than analog radios given the same power levels. Digital radios can use slightly less bandwidth for the same audio quality, packing more channels into a band, but that's not very relevant for aviation.

The antenna size varies by the frequency, regardless of whether the radio is analog or digital: the higher the frequency, the smaller the antenna. Switching to digital wouldn't make the antennas any smaller, unless the frequency band changes also. A higher frequency band would make the antennas smaller, but finding a new large frequency band for aviation use worldwide would be very difficult.

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  • $\begingroup$ A requirement for a single signal transmitted at any one time is not an inherent property of a digital modulation. TDMA (time division, multiple access) is a well-established method of allowing multiple transmissions to share a single frequency range that really can only be implemented with digital modulation, as it requires transmitting bursts of data in faster than real time, with a waiting period in between bursts. TDMA does however usually require that transmitters cooperate somehow, which could be problematic in an environment where the set of transmitters in range changes continuously. $\endgroup$ – a CVn Jun 23 '19 at 17:41
  • $\begingroup$ @aCVn TDMA, CDMA, and other digital multiplexing schemes aren't practical without something like a mobile phone tower coordinating things, which is why digital two-way radio systems (meaning not mobile phones) don't use such schemes. $\endgroup$ – rclocher3 Jun 24 '19 at 13:47
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A MATTER OF COVERAGE:

Digital radio requires higher emitting frequency using pulse modulation or other techniques

analog modulation requires a carrier which could be of low frequency such as in VHF or better in HF

For instance HF radio communications are used in those areas where VHF radio communications are not available due to their limited signal coverage, HF radio signals propagate through ground waves, that are reflected and /or refracted, so the transmission is not linear and will transmit very far.

So analog transmission may have a much larger coverage

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