The 578 shares its APRS architecture with the 878, which makes sense since AnyTone builds the CPS around the same feature set across the mobile and handheld lines. The setup steps are nearly identical, but a mobile radio adds a couple of wrinkles worth calling out, starting with the GPS antenna itself.
Mount the GPS Antenna With a Clear Sky View
Unlike a handheld with GPS buried in the case, the 578 uses an external GPS antenna that has to be mounted somewhere with a real view of the sky. On the Jeep, that means the roof or the top of the dash, not tucked under the windshield trim. A weak or obstructed GPS antenna is the most common reason a mobile APRS setup looks fine in CPS but never actually reports a position.
Enable APRS and GPS in CPS
Same as the 878, go to Tools, then Options in CPS and check both APRS and GPS to unlock the APRS branch in the settings tree. Without this step the APRS configuration screens stay hidden.
Build an Analog APRS Channel
Set a channel to 144.390 MHz FM and link it to your APRS RX/TX profile with your callsign, SSID, and digipeater path. I run the mobile at KZ7K-9, which is the conventional SSID for a mobile station, keeping it distinct from the -7 I use on handhelds. WIDE1-1,WIDE2-1 remains my go-to path.
Set a Beacon Interval That Matches Highway Speed
Since this radio does not have smart beaconing, a mobile install needs a shorter fixed interval than a stationary base would. I run mine around 2 to 5 minutes when the Jeep is moving, which keeps the track reasonably smooth on aprs.fi without hammering the frequency on longer stops.
Assign a Front Panel or Mic Key
Program one of the front panel keys or a mic function key to APRS Send so you can push a manual beacon without taking your eyes off the road for long. I like having this available separate from the automatic interval, especially right after startup when I want to confirm the radio is transmitting before I trust the automated beacon to do its job.
Verify on the Road
Write the codeplug, start the vehicle, and give the GPS antenna a minute or two to acquire a fix once you are moving or parked somewhere open. Send a manual beacon and check aprs.fi. If the position is stale or missing, the GPS antenna mounting location is the first thing I would check, followed by confirming APRS and GPS are actually enabled in CPS.
Related reading: What Is APRS? · Setting Up APRS on the Kenwood TH-D75A · Configuring APRS on the AnyTone AT-D878UV II Plus