Dear friends,

I bought the combination GTN 750 and GTN 650. The problem is that the 650 prefers the COM 2 frequency and when I select the NAV 2 frequency it changes after a time back to COM 2.

Is it possible, that the 650 prefers the NAV 2 frequency and changes automatically to that when I selected COM 2?

 Hi,

AFAIK this is how the GTN is operated: changing NAV frequency requires toggling the input knob to NAV first, and this reverts automatically to COM after a short while.

8 hours ago, josef050153 said:

I bought the combination GTN 750 and GTN 650. The problem is that the 650 prefers the COM 2 frequency and when I select the NAV 2 frequency it changes after a time back to COM 2.

 

Yes.  Sort of... 

After a period without input, the GTN reverts to a no selection state.  Note that neither of the COM or NAV windows are highlighted (back-lit).  However the standby frequency on the COM side appears in blue digits while the standby frequency on the NAV side appears in white digits.  The GTN in that regard is in a bit of a null state, waiting for input. 

When in that state, the first press of the inner knob actually selects and highlights the NAV stby frequency, activating it for tuning.  Successive presses of the inner knob switch the GTN back and forth between NAV and COM.

Now, when in that same null state, if you instead twist either the inner or the outer knob, that first twist will instead activate and begin to change the COM frequency.  Why from that null state are twists prioritized to COM?  Well, it has to choose one or the other, doesn't it!  Saves making an unneeded press of the inner knob. So twist for COM, press for NAV.

When NAV is selected and highlighted, the NAV stby frequency digits change to blue.  If you switch to NAV and just leave it alone, after five seconds the highlight goes away, but the stby frequency continues to appear in blue digits, indicating it is active for tuning.  After 30 seconds in NAV with no additional input, the GTN reverts to the null state, the NAV stby digits change from blue to white, and the COM stby digits change from white to blue.  The side that appears in blue digits is always the side active for tuning.  All it takes is a glance, and the knowledge of the 30 second no-input period from NAV to null.

Fire up the standalone Garmin GTN Trainer and you will be able to confirm this is coded in by Garmin.  Perhaps Garmin assumes more frequent changes to COM frequencies since after all you are assumed to most often be using their wonderful GPS to navigate rather than the COM radio.

Note that Garmin's GNS gauges also prioritize to COM after a similar period of no input on the NAV frequency.

 

 

 

Edited February 27, 20206 yr by fppilot

@fppilot Thank you for sharing this info!