[Harc] APRS, GPS, DMR and Privacy

[Emily Mazzone]

Hello everyone,

The lengthy message below is from a friend, who is a lot smarter than me
(about most stuff in general), regarding the new mobile rig Santa brought
me for Christmas (long story). I am curious as to anyone's experience with
this particular topic. The radio in question is the Chinese-made AnyTone
AT-D578UV III Pro which, as of Sunday, is waiting for me to get on the air.

The back story is that I am a curious person and like to know stuff, so I
asked this friend about the fancy modern bells and whistles and how they
impact *privacy*. Why? Well, I had just been doing some digital privacy
review work on my own footprint after yet another data breach, and it was
on my mind.

This is what he said:

* * *

Not familiar with the radio, but looks like a good package.

- For that radio, I would disable Bluetooth and only enable when actively
using it.
- Disable APRS/GPS unless intentionally needing to broadcast your location
to others. Make sure you are disciplined in turning APRS off well before
arriving at locations that are sensitive (like your home). Keep in mind if
you do utilize APRS, a threat actor could start to develop a 'pattern of
life' about you using a site like https://aprs.fi to study your historical
locations/movements.
-For DMR operation, keep in mind that there is a good amount of metadata is
exposed and can be monitored when you are operating on DMR. These include
things like registration bursts, roaming scans, slot sync behavior,
APRS-DMR checks, and network presence frames

Here is an explanation of the DMR privacy threats:

Registration bursts
When your radio connects to a DMR repeater or network, it briefly sends a
digital “hello.”
This announces that your radio ID is now present on that system.

Roaming scans
If your radio is set to automatically find the best repeater, it
periodically “listens around” and may briefly signal nearby repeaters to
see which one it can use.
This can reveal that your radio is active in the area.

Slot sync behavior
DMR uses two time slots on each frequency. Your radio constantly listens
for timing markers so it knows exactly when it is allowed to transmit.
This creates a detectable digital timing footprint even when you are not
talking.

APRS-DMR checks
If GPS/APRS is enabled, your radio periodically sends short data packets
that include your location and radio ID.
These are automatic tracking beacons, even when you do not press the talk
button.

Network presence frames
On connected DMR networks, your radio periodically sends status messages so
the network knows you are still online.
This is similar to a device checking in with a server — it shows that your
radio is present and active.

* * *

I plan to do some digging as well but wanted to run it by you all first.

Thanks for reading and I look forward to any insights.

73
Emily KN6ZWG
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