[Ground-station] Are Multi-Carrier Data Modes Illegal in Amateur Radio?

[Michelle Thompson]

Also, our Neptune project is an OFDM physical layer and data link project,
so relevant over there too.

Good points on ID and scrambling. Not sure yet how to or whether to fold
that into an emissions designations article, but I did update it a bit to
include more context, fixed typos and formatting.

-Michelle Thompson



On Thu, Apr 24, 2025 at 10:24 PM Ron Economos via Ground-Station
<ground-station at lists.openresearch.institute> wrote:

> Mike McGinty W2FBI is working on a ham radio band LTE implementation. He
> has a demo running with a Band 40 femtocell from China. Band 40 is 2300 to
> 2400 MHz TDD which overlaps the ham band at 2300 to 2310 MHz.
>
> He's concerned about the legality of LTE in the ham bands. The first issue
> was if OFDM is legal. At this point in time, we all agree that paragraph
> 97.307(f)(8) makes OFDM entirely legal above 51 MHz.
>
> The other issues are how to ID and encryption. For ID, I claim everyone
> running FT8 is violating 97.119(b), so it's moot. Therefore, all you have
> to do for ID is send your call sign in the clear somewhere in the signal.
>
> Encryption is a bit of a can of worms. We believe there's a null cipher
> available, but it needs to be tested. It's also believed that some parts of
> the specification are always scrambled, so that needs to be fully
> understood.
>
> Mike has a Discord server for the project. E-mail me if you want an invite.
>
> Ron W6RZ
> On 4/24/25 19:39, Jan Schiefer via Ground-Station wrote:
>
> Is there somebody planning to experiment with OFDM-like signals for ham radio, or is this all purely hypothetical?
>
> What I would find more interesting is multi-band carrier aggregation on HF. For example, simultaneously sending part of the signal on 80m and part on 40m, with some smart coding based on propagation characteristics at the time of the transmission. In theory, this should give you a pretty robust signal on e.g. NVIS.
>
> Would something like this be subject to the same questions as far as the legality goes?
>
> And I am sure there is another can of worms on this shelf with the label “MIMO” on it. Maybe let’s keep this one where it is.
>
> Cheers,
>     Jan, ac7td
>
>
>
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