GTX328/330 GPS Serial In

[flyvans.com]

Hi,

i'm troubleshooting the last snag in the avionics wiring.
for some reason, the GTX328 transponder doesn't get the GPS data from the Garmin GPS-18 mouse (for the automatic on/flight time counter function), even though i checked the wiring/pins several times.
Also the same GPS feeds the Trutrak just fine (the tx line of the gps is split to the trutrak and the transponder).

anybody encountered a similar problem? what data format is the transponder expecting? what baud rate? which (nmea) message does it need? (GPRMC?)
unfortunately the install manual does not cover these points at all.

the garmin gps-18 is configurable, so there is some possibility for error in there, however i set it to mostly default values, so one would expect garmin to work with garmin ;-)

oh and by the way, the other serial in #2 (altitude encoder from the efis) works just fine.

thanks for some hints!

bernie

[mburch]

Unfortunately, I don't believe these two devices are compatible. Last time I checked, the Garmin transponders are not capable of receiving NMEA serial data, which is what a GPS 18 wants to transmit. Something to do with certified versus non-certified would be my guess.

mcb

[flyvans.com]

hi matt,

thanks for the info... that sucks...
in that respect i'm disappointed with garmin. the install manual is so generic it doesn't even mention these basic technical details...

also, there's no reliable and complete description of the auto-turnon feature, e.g. would it work without gps or squat switch...
guess, we'll just have to investigate further...

and even the certified/non-certified argument is pretty weak.
it's got probably more to do with making the customer purchase a garmin panel gps along with it $$$.

also, you're the first one (after many garmin support and sales staff) to actually know about it and confirm that it doesn't work with nmea... so i can quit trying ;-)

there's a slight possibility that we might be able to make it work through the afs-arinc429 extender box.
guess in the end, the feature won't be worth the hassle.

rgds, bernie

[Radomir]

If you're sending encoder data from an EFIS, you probably won't need the gps hookup at all. At least, that's how my 327 works (I have a GRT EFIS.. not AFS.. but I'd expect 'em to work similarly if not the same)... And if it doesn't work, it's something that AFS could easily add in the data they send over to the transponder..

Again, I don't have any GPS connected to my transponder and it works just fine, including auto-on and auto-stdby... so before you get too disapponted.... I'd check if it works through EFIS...

[flyvans.com]

hi radomir,

so it's an extension/depending on the pressure altitude/(air data) format then... what kind of input format does grt want you to specify?
afs has us use "icarus" format, don't know wheter that has the extensions required for that case...
will get in touch with rob hickman, he might know more about it...

kind regards,
bernie