Presumably the 125MHz emissions are within the FCC allowed envelope anyway, so this isn’t doing anything to exceed normal emissions limits. This only works in a quiet RF environment, as noted in the README.
There is no need to be concerned about this signal reaching aircraft or otherwise interfering with normal transmissions.
That's all sort of besides the point anyway as nav aids use the lower end of the aviation band, 125MHz is used for AM voice where the interference would be, at worst, audible but not strong enough to cause problems unless reception was already extremely marginal.
Or to put it differently, two pilots hitting their PTT at the same time is already causing far more disruption to operations in the 125MHz range than this thing ever would.
As you mention, this is toggling the expected 125Mhz on and off. It's not noise, it's "the signal".
From a regulatory perspective, there's a big difference between intentional and unintentional radiators.
The most advanced example of this kind of inadvertent transmission I've seen is Fabrice Bellards DVB-T transmitting with a standard VGA card:
But... yeah. You could tune into VGA monitors up to a mile a way using consumer hardware, and reception is perfectly legal (lots of case history to back this up)!
I figured my pitch would be to walk in with a briefcase setup, flip a switch, and show them what the receptionist was working on. Then ask if they were worried if competitors could know what they were working on (not a threat, just bringing awareness), or would they be were interested in some expensive cables/hardware.
Now that the kids are grown up and divorce pending, I've debated getting back into the netsec field. Lots of fascinating angles to be had in unexpected hardware boundaries... and my background in data science/machine learning/DSPs could prove fruitful in signals reconstruction...
I also got reminded about the method to send data from one computer to another over low frequency sound https://www.extremetech.com/computing/171949-new-type-of-aud...
https://arstechnica.com/information-technology/2016/08/new-a...
FWIW very brief example of 125MHz tone loss when going to 10MHz demonstrated here when my slow internet gets done uploading:
(Unpleasant sound warning)
Also I'm not talking about 30 miles away...but if a completely intact cable can be detected with a directional antenna from 100m, an intentionally buggered patch cable installed at a client site for this purpose could pose a bigger concern for pilots in the area. (edit: I might be more tuned in to this (har har) because I live in the flight path of a medical helicopter that flies over at ~500' almost daily.)
Ham folks can seem a bit hair-triggered chicken littles with RF hygiene but it's the product of decades of fighting noise from people that aren't aware of the externalities of their actions.
Another thing is that regulations don't only consider radiated power. Constant-level spurious transmissions are sometimes tolerated to a higher degree compared to modulated ones (e.g. in some bands maximum allowed interference is determined by quasy-peak level, not power). This is exactly because modulated interference (which is what this produces) is more harmful to communications systems.
Take powerline ethernet where the power levels are "low" but still can cause significant issues[2].
[1] http://www.arrl.org/part-15-radio-frequency-devices#Myths
[2] http://www.elmac.co.uk/RF_Emissions_of_Powerline_Ethernet_ad...
Low risk overall but it's a good reminder.
It's very possible to transmit illegal power levels with software mods, or even carefully crafted data packets in some cases.
I'm sure many devices on the market are not compliant. I follow lists of products removed from market for non-compliance and there are plenty each week. But the fact is that, if you're not in one of the categories that are under special scrutiny (aerospace, automobile, medical, etc.) or do something grossly incompetent (e.g. interfere with a mobile operator or someone else with a similar power to put you into the regulatory spotlight) you're unlikely to get into trouble for shipping a non-compliant device.
Make someone's Wi-Fi a bit slower and a bit more packet-lossy? Chances are nobody will care. It's a sad state of affairs really because pervasive radio interference is just making things worse for everyone.
Another classic example is early cellphones that you would pick up on stereo systems etc. - "dat-dara-dat-dara-dat-dara-dat-dara-daaaaaa" going out in full blast.
The first two options are somewhat expensive, the NRE for the power supply design isn't attractive to manager types and conductive coatings for plastic or a metal enclosure are not the cheapest options. But if you're dead set on compliance it's better to frontload the design costs instead of iterating 3 times before you get to market.
Anyway, we totally could have made a transmitter out of that thing.
(CubicSDR ran on the same DELL machine, however both tones disappeared after disconnecting the antenna from the SDR)
