4 ms·

It has nothing to do with Motoroa, TDMA, or 5G. If the wanted signal is very weak (eg from a distant aircraft using VHF AM), and there is an interfering signa

It has nothing to do with Motoroa, TDMA, or 5G. If the wanted signal is very weak (eg from a distant aircraft using VHF AM), and there is an interfering signal on the same channel, the emergency communications will be distrupted.

simfree 4y ago
Aircraft using the VHF band with amplitude modulation is going to perform much differently than a police repeater and it's local upstream only amplifiers interacting with low wattage fixed handhelds and medium wattage car mounted mobile radios. Pivoting topics is a bad faith conversational tactic FYI, and doesn't follow HN's guidelines. I encourage you to fully read the guidelines linked at the bottom of the page.
- Johnythree 4y ago
  Nevertheless, the threat is to public safety communications. And not all Public safety use TDMA (or whatever). Aircraft communications is probably the most vulnerable, but so are HF/VHF marine operations, military and a host of others. TDMA amplifiers could well be a problem in your country, but the whole point of the discussion is that transmitting a wide band of RF hash will certainly be detrimental to thousands of other radio users, whether or not they are using a TDMA public network.
  - simfree 4y ago
    Amplifiers are often protocol agnostic. Whether your amplifying TDMA, Trunked radio, CDMA etc. Aviation needs to modernize, I have zero sympathy for the aviation community getting constant hallpasses on ancient altimeters that lack filters to reject RF from nearby frequencies, leaded avgas, and abysmal working conditions for those stuck in the industry. The FAA dragging their feet in the USA trying to act like they should never have to test how interference affects hardware on planes is insane, they waited till well past when 3.5Ghz went into cellular use to make any effort to performance test altimeters for band conformance. The FCC's timelines are long, the FAA had at least half a decade heads up of when the 3.5Ghz auction would occur, and additional time after the auction before Verizon and AT&T put the spectrum into service. We have waited 25 years past when everyone else stopped using leaded gas to get rid of leaded Avgas[1]. As a Seattleite who grew up with families made up of Boeing Engineers, the problem of vulnerable radio transmissions from aircraft could be resolved with a network of reception sites just like Gogo uses at a much higher frequency allocation. This problem is just not a priority for the Aviation community, they would rather not invest in better equipment and infrastructure. 1 - https://qz.com/leaded-aviation-fuel-is-prompting-bipartisan-outrage-am-1849355733 https://qz.com/leaded-aviation-fuel-is-prompting-bipartisan-... Edit: Trunked, not Truned
    - Johnythree 4y ago
      Aircraft use AM on VHF because it is still the most efficient mode. Unlike FM it doesn't suffer from the "Capture Effect" so you can tell if a weaker signal is trying to get through on a busy channel. And unlike FM it doesn't suffer from the Threshold Effect where weak signals suddenly disappear into the noise. And of course Digital modulation is ruled out by both of the above considerations. The only mode which is more efficient (for weak signal communications) is Single Sideband, and that can't be used in aircraft due to Doppler shift. It is true that local reception sites can help, but they are not possible over water. Perhaps one day satellite systems might finally replace aircraft AM. The problem at present is the cost for fitting to light aircraft.
      - anticensor 4y ago
        Why not QPSK over VSB like used in broadcast satellites?
        Johnythree 4y ago
        The problem with QPSK in particular is a loss of phase lock in marginal conditions, or with interference. It would require higher complexity, with no improvement for marginal signals. One possible improvement would be "Synchronous AM" (eg 1/2 of a QAM signal) but that will also lose phase lock in weak signal conditions, eg when it is most needed.

simfree 4y ago

Aircraft using the VHF band with amplitude modulation is going to perform much differently than a police repeater and it's local upstream only amplifiers interacting with low wattage fixed handhelds and medium wattage car mounted mobile radios. Pivoting topics is a bad faith conversational tactic FYI, and doesn't follow HN's guidelines. I encourage you to fully read the guidelines linked at the bottom of the page.

Johnythree 4y ago
Nevertheless, the threat is to public safety communications. And not all Public safety use TDMA (or whatever). Aircraft communications is probably the most vulnerable, but so are HF/VHF marine operations, military and a host of others. TDMA amplifiers could well be a problem in your country, but the whole point of the discussion is that transmitting a wide band of RF hash will certainly be detrimental to thousands of other radio users, whether or not they are using a TDMA public network.
- simfree 4y ago
  Amplifiers are often protocol agnostic. Whether your amplifying TDMA, Trunked radio, CDMA etc. Aviation needs to modernize, I have zero sympathy for the aviation community getting constant hallpasses on ancient altimeters that lack filters to reject RF from nearby frequencies, leaded avgas, and abysmal working conditions for those stuck in the industry. The FAA dragging their feet in the USA trying to act like they should never have to test how interference affects hardware on planes is insane, they waited till well past when 3.5Ghz went into cellular use to make any effort to performance test altimeters for band conformance. The FCC's timelines are long, the FAA had at least half a decade heads up of when the 3.5Ghz auction would occur, and additional time after the auction before Verizon and AT&T put the spectrum into service. We have waited 25 years past when everyone else stopped using leaded gas to get rid of leaded Avgas[1]. As a Seattleite who grew up with families made up of Boeing Engineers, the problem of vulnerable radio transmissions from aircraft could be resolved with a network of reception sites just like Gogo uses at a much higher frequency allocation. This problem is just not a priority for the Aviation community, they would rather not invest in better equipment and infrastructure. 1 - https://qz.com/leaded-aviation-fuel-is-prompting-bipartisan-outrage-am-1849355733 https://qz.com/leaded-aviation-fuel-is-prompting-bipartisan-... Edit: Trunked, not Truned
  - Johnythree 4y ago
    Aircraft use AM on VHF because it is still the most efficient mode. Unlike FM it doesn't suffer from the "Capture Effect" so you can tell if a weaker signal is trying to get through on a busy channel. And unlike FM it doesn't suffer from the Threshold Effect where weak signals suddenly disappear into the noise. And of course Digital modulation is ruled out by both of the above considerations. The only mode which is more efficient (for weak signal communications) is Single Sideband, and that can't be used in aircraft due to Doppler shift. It is true that local reception sites can help, but they are not possible over water. Perhaps one day satellite systems might finally replace aircraft AM. The problem at present is the cost for fitting to light aircraft.
    - anticensor 4y ago
      Why not QPSK over VSB like used in broadcast satellites?
      - Johnythree 4y ago
        The problem with QPSK in particular is a loss of phase lock in marginal conditions, or with interference. It would require higher complexity, with no improvement for marginal signals. One possible improvement would be "Synchronous AM" (eg 1/2 of a QAM signal) but that will also lose phase lock in weak signal conditions, eg when it is most needed.