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What if the Internet Goes Down? - 15 Jan, 7PM CET (lemmy.ml)
submitted 8 months ago by to c/technology@lemmy.world
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[–] 4 points 8 months ago (2 children)

For LF and MF, you typically want narrow signals, not spread spectrum. It's hard to make wide band antennas for such low frequencies and propagation can change a lot in just a few tens of kHz.

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  • [–] 2 points 8 months ago (1 child)

    I see

    In your opinion is there anything useful we can do with that part of the radio spectrum as those stations switch off, or are those frequencies going to be silent in the future? Will they be turned over to hobbyists maybe? (or would the power requirements be too high at those frequencies?)

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  • [–] 3 points 8 months ago

    The AM broadcast stations aren't going anywhere, at least in the US. Above the broadcast band is mostly aircraft, marine and the 160 meter ham band. None of that is likely to change.

    Below the AM broadcast band are non directional beacons. Those are slowly being decommissioned. Eventually they will all be gone and that spectrum may get repurposed. I don't know what the spectrum may get used for, but it would be nice if the 630 meter ham band was expanded.

    LF and MF can be used at low power. The 2200 meter ham band has a power limit of 1 watt EIRP and the 630 meter band has a limit of 1 or 5 watts EIRP depending on the country. Actually radiating that much power is difficult because it's not practical to build an efficient antenna. Luckily there is no limit on how much power the amplifier can put out, so we can put hundreds of watts into a very inefficient antenna. Narrow band digital modes work great on those bands.

    In the US, we have LowFER, which allows hobbyists to use 160-190 kHz for experimental use without a license. The power limit is 1 watt input and the transmitting antenna is limited to 15 meters. People still manage to make long distance contacts with those significant limitations.

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