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My understanding is that the concern is not interference with voice radio but interference with the more sensitive analog radionavigation equipment, e.g. VOR an

My understanding is that the concern is not interference with voice radio but interference with the more sensitive analog radionavigation equipment, e.g. VOR and ILS. These both aren't used on the ground and don't work on the ground anyway because of antenna orientation and other issues. VOR and ILS are very old and very simple technologies (at least as radio goes), making it fairly plausible that radio interference in particular bands could skew the ILS needle and cause a badly failed landing approach.

jrockway 10y ago
But remember that both GSM and ILS/VOR/DME are licensed radio services, and thus shouldn't interfere. The speakers you hear the TDMA modulation in have a sticker on them that says "This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." Indeed, it does accept the interference that causes undesired operation.
- jcrawfordor 10y ago
  This is a bit of a misinterpretation of Part 15. Part 15 devices bear the "must accept" language to indicate that they enjoy no particular regulatory protection from interference - the operator of a part 15 device may not compel action on the part of another person because that person's lawful operation is interfering with the part 15 device. Licensed services do enjoy regulatory protection, but that protection doesn't change anything physically - it just means that there is a regulatory remedy when interference is a problem. And one of those remedies is FCC regulations about where other devices can and cannot be used. While radionavigation equipment should be built to high standards for interference rejection, their being a licensed service is in no way a guarantee that other devices won't cause problematic interference. It just means that when other devices do cause interference, FCC enforcement is a possibility.

jrockway 10y ago

But remember that both GSM and ILS/VOR/DME are licensed radio services, and thus shouldn't interfere. The speakers you hear the TDMA modulation in have a sticker on them that says "This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." Indeed, it does accept the interference that causes undesired operation.

jcrawfordor 10y ago
This is a bit of a misinterpretation of Part 15. Part 15 devices bear the "must accept" language to indicate that they enjoy no particular regulatory protection from interference - the operator of a part 15 device may not compel action on the part of another person because that person's lawful operation is interfering with the part 15 device. Licensed services do enjoy regulatory protection, but that protection doesn't change anything physically - it just means that there is a regulatory remedy when interference is a problem. And one of those remedies is FCC regulations about where other devices can and cannot be used. While radionavigation equipment should be built to high standards for interference rejection, their being a licensed service is in no way a guarantee that other devices won't cause problematic interference. It just means that when other devices do cause interference, FCC enforcement is a possibility.