You can also use as an external antenna, any Garmin On The Trail device that has NMEA OUT capability (using a USB cable).

I use the 60c or 60csx as an antenna (Setup>Interface>Serial Data Format>NMEA In/NMEA Out).
In TopoNavigator6 Preferences, I choose Com Port>Garmin USB and Baud rate>4800
Then I press the GPS connect button from the NMEA menu and the program goes into Tracking/Navigating Mode.

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There is also a dedicated page view (F5) for Tracking/Navigating.

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