"Do It Yourself" airborne proximity warning device

On Friday, October 5, 2018 at 1:41:30 PM UTC-7, Andy Blackburn wrote:
On Friday, October 5, 2018 at 9:06:01 AM UTC-5, Dave Nadler wrote:

PS: Paper above doesn't mention REQUIRED FCC certification (and analogous
foreign certifications) - expensive, and REQUIRED.

Not to be the turd in the swimming pool, but I have some concerns about this.

Having worked on a consumer product that used the LoRa physical layer operating in the ISM band (Flarm is an ISM band device), I can attest to what Dave says and why it's important. Without specific rules regarding power, duration and frequency hopping, for example, it is easy to end up with devices that create so much congestion that they make the band useless for everyone else. Think of this as a glider with a perpetually stuck mike on their radio. This device doesn't appear to do this in isolation, but networks rarely get congested with small numbers of devices connected, even if they are poorly behaved.

It's my understanding that the over-the-air Flarm protocol has specific (and secure) methods for congestion control through timing broadcasts versus the GPS clock and this is how it is able to accommodate reasonable numbers of aircraft in proximity without too many transmissions colliding (pun intended) and blocking each other out. It is not at all clear to me whether this device has implemented the Flarm protocol or if it simply broadcasts without any congestion control under the presumption that not too many gliders will be flying at the same time. It seems from reading the GitHub documentation like maybe it is using a hack to get around this restriction which could create congestion problems - particularly in larger numbers.

Moreover, it doesn't appear that the Chinese manufacturer of these boards has pursued any FCC licensing (I doubt it) and even if they had part of the FCC licensing requires the complete device in its physical enclosure to ensure that RF pollution doesn't flood out of the device in unpredictable ways.

Mostly I have questions and suppositions as I don't know exactly what work has been done and I'm not an RF or networking engineer, but I'd be a bit concerned if one of these devices showed up at a big OLC camp. Also, beware of ramp checks if you have unlicensed (I guess technically that means illegal) devices operating on the same frequency as licensed safety devices. The Feds might frown on that. If I showed up at the airport with home-brew ADS-B Out kit in my glider I bet I'd get at least a sternly-worded letter from the FAA.

I have a lot of respect for this effort, but there is a potential need for significant caution. Many of our fellow pilots rely on this technology to keep them safe. If that technology were inadvertently being jammed, they'd have no way to know.

There are other issues with how the data port spec is or isn't implemented, but that's a whole other kettle of fish. If you are going to bet your life on a technology it's probably good for it to work as close to 100% of the time as you can manage.

Respectfully,

Andy Blackburn
9B

The FAA doesn't regulate the RF (electromagnetic) spectrum; that is the job of the FCC. It is HIGHLY unlikely that the FCC will show up at your local ramp with spectrum analyzers - they respond to serious complaints, and, then, with much plodding. Your fellow pilots, however, might get on your case if they figure out your equipment is interfering with theirs. The ISM band is pretty much the Wild West of the RF spectrum, and the FCC doesn't get involved.

https://en.wikipedia.org/wiki/ISM_band

Tom