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

[w2fbi]

Thanks Ron!

Jan,

Yes, as mentioned I'll be operating LTE between 2305-2310 and 2390-2400 MHz.

The only question is what gyrations I will have to make to comply with 
regulation.

This is not a hypothetical, this is the last crossing of 't's and 
dotting of 'i's before I operate it outside of the workbench.

What's your take? I believe 97.307(f)(8) is a solution to the authorized 
emissions issue for my specific situation, but there are still questions 
left as far as codes and techniques.
These have implications for 97.119(b)(3), and that's assuming the usage 
of RTTY alone in that section being authorized for ID is not 
problematic, which is the same assumption almost every digital mode is 
making right now.

I'm not convinced that's per the letter, but it's clearly not been 
considered a major issue, either.

As for encryption, I am going to generate keys based on callsign and 
with a published OP for the network, meaning all relevant keys will be 
published or trivially derivable from public information. As long as UE 
identification can be made to work, this works great.
I think there are some arguments that this part is not really necessary, 
but I am more interested in getting people onboard with the idea and 
operating in alignment with the most conservative interpretations I can 
find of the regulations, not pushing the envelope of legality.

Ham LTE is already one of those topics where people are tend to start 
between skeptical and hostile. This is what was driving me to try and be 
careful and ultimately ask for help with this; I want to be able to 
articulate not just that it's not illegal, but that Ham LTE is 
explicitly permitted. Unfortunately I found some sticky spots which 
would appear to impact far more than just my projects.


73

Mike W2FBI
P.S. My thanks to Michelle and Paul for getting a lot more eyes on this, 
and for phrasing it far more clearly than I could!

On 4/25/25 01:23, Ron Economos via Ground-Station 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
>>