GRT Avionics

The ADS-B rules allow for an anonymous mode when squawking 1200. Details can be found in AC 20-165B starting on page 26:
http://www.faa.gov/documentLibrary/medi ... 0-165B.pdf

I am using a GRT Mini-X as the control head for a TT22.

Does the Mini support ADS-B anonymous mode?

If not, could this be implemented?

Thank you,

-Dj

No. Anonymous mode is only possible with UAT devices. All mode S transponders send your unique mode S address, so big brother knows who you are. IMHO this is not a big deal. Airspace rules are there for a reason, don't break them. If you do, expect to take your medicine.

Bobturner wrote:No. Anonymous mode is only possible with UAT devices. All mode S transponders send your unique mode S address, so big brother knows who you are. IMHO this is not a big deal. Airspace rules are there for a reason, don't break them. If you do, expect to take your medicine.

Not sure why you are bringing up airspace rules. No one is proposing any breakage of them.

In this case the Mode S address is set within the Mini, which also controls all functions of the TT22 transponder. It should simply be a matter of software to implement the anonymous mode as described in the ADS-B Advisory Circular.

Read your document again. Mode S transponders must transmit their mode S address. Nothing else is allowed. UAT devices may transmit a random code if and only if a mode C transponder is being used. If mode S is being used then the random feature must be turned off.

Bobturner wrote:Read your document again. Mode S transponders must transmit their mode S address. Nothing else is allowed. UAT devices may transmit a random code if and only if a mode C transponder is being used. If mode S is being used then the random feature must be turned off.

That seems silly. Someone must have been smoking crack when they made those rules. What possible logic would they have for only allowing anonymous ADS-B for UATs and not ES transponders?

-Dj

It's not just S-ES transponders, it is plain mode S too. That's because mode S transponders are addressable - if two planes are too close, so the radar is confused, ATC can just ping one, then the other, in separate sweeps. That's why they need the mode S address, to "address" a specific transponder. It has nothing to do with ADSB. It is only if you do not have a mode S that you are allowed to transmit a fake mode S code, e.g., UAT and mode C transponder.

According to the algorithm in the documentation, using anonymous mode generates a unique, random 24 bit code. Each mode S would still have a unique code and still be individually addressable.

I have not yet found a technical reason why the anonymous mode would not work equally as well for 1090ES transponders as it does for UAT.

There is no technical reason - it's just a rule! Currently UATs receive info from transponders, but don't send transponders anything. I think the FAA thinks pilots will behave better if they think big brother is watching. Maybe they're right.

Bobturner wrote:the FAA thinks pilots will behave better if they think big brother is watching. Maybe they're right.

I'm not convinced that is the case. I'm sure they realize the "bad" people likely know about a very simple invention called an off switch, or would just equip with a UAT versus ES, or would simply not equip with ADS-B Out at all since it is only required for specific airspace.

There are many valid reasons for not wanting the public to be able to track flights and easily identify aircraft. Here is one good article on it:

http://www.wsj.com/articles/SB100014241 ... 3003145370

There is no logical reason for not allowing an anonymous mode for ES.