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Garmin GTX327: GPS input

McFly

McFly

Well Known Member
I just installed a new GTX327 transponder but did not hook up the GPS input (yet?). I was under the impression that the function of the GPS was to automatically change the mode from ?standby? to ?alt? when the plane gets underway.

Well my transponder already does this without the GPS input. I assume it knows this by the pressure change it gets from the encoder, which in my case is a Dynon D-10A (also not connected to the GPS). However: when I land, it does not automatically go back to ?standby? mode.

This is a lot of background to ask ?What does the GPS input do on this transponder?? Thanks.
 
Someone will have to explain it better than that

I was hoping someone could dumb it down for me since that manual has been my info source thus far.

But thanks anyway Kahuna!
 
Are you waiting long enough? After you "land" there's a delay in switching to standby.. this delay (timeout) is configurable in the setup..

Manual has this explained as well.
 
Don't need it for that

You do not need GPS input to the transponder for the auto feature to go to and from standby. Mine works fine and it not wired to the GPS, just a serial connection to the encoder in the GRT.
 
You do not need GPS input to the transponder for the auto feature to go to and from standby. Mine works fine and it not wired to the GPS, just a serial connection to the encoder in the GRT.
Click to expand...

Thanks hevansrv7a. So what is the GPS input for then?? This question also stumped the guy at Stark when I told him the auto feature was working without GPS input.:confused:
 
From what I've read, the GPS signal is given the highest priority as far as detecting when the aircraft is airborne. If there is no GPS signal, the unit uses other methods. I got snippets of that from section 5.

However a GPS signal does provide some modicum of additional information can be displayed.

From section 5.2.8 of the installation manual, Revision L:
"Depending on the selected inputs on Channel 1 and Channel 2, this page displays the information
received on the channel. If GPS is selected as an input, ground speed (GSPD), latitude (LAT), longitude
(LON) and track (TRK) can be viewed."

Cheers,
 
Guy Prevost said:
From section 5.2.8 of the installation manual, Revision L:
"Depending on the selected inputs on Channel 1 and Channel 2, this page displays the information
received on the channel. If GPS is selected as an input, ground speed (GSPD), latitude (LAT), longitude
(LON) and track (TRK) can be viewed."
Click to expand...
I've always wondered about this feature of the 327/330. OK, Garmin should know how to read and decode an NMEA string out of a GPS, fair enough, but why do that inside of a transponder box? How useful are lat/long/track to a normal mode C transponder.

But, hey!, wait... could it be that snippets of code coming from an ADS-B addon are already there, for some reason? ;)

I wonder if Garmin will soon be releasing a 33x transponder with mode S and ADS-B, by simply tweaking the existing 330 hardware, and charging the users big buck$... :eek:

Ciao, Luca
 
Thanks for all of the input. I was assuming that I had to be missing something but apparently not.

BTW: The only way to view the GPS info is to power up the unit in configuration mode, a mode when the unit is not squawking. I?m cutting the cord (harness wires for the GPS input). Garmin, where is your head at?
 
McFly said:
BTW: The only way to view the GPS info is to power up the unit in configuration mode, a mode when the unit is not squawking. I?m cutting the cord (harness wires for the GPS input). Garmin, where is your head at?
Click to expand...
Why? The GPS input is the more "reliable" way to determine when the aircraft is airborne and it also activates the flight timers. Using the encoder, there will be some lag in the response. Also, using the encoder to switch modes is a recent addition to the GTX -327 code. If for some reason you have to "borrow" an old unit with old software, you auto mode switch feature would not work.
 
Why? The GPS input is the more "reliable" way to determine when the aircraft is airborne and it also activates the flight timers. Using the encoder, there will be some lag in the response. Also, using the encoder to switch modes is a recent addition to the GTX -327 code. If for some reason you have to "borrow" an old unit with old software, you auto mode switch feature would not work.
Click to expand...

Maybe this is a matter of preferance but since you asked;)

IMHO it is merely extra weight, extra complexity and extra wires to sort though when trouble shooting anything electrical. All for a redundant feature that has little value to me in the first place. I wouldn?t say the GPS input is more reliable either, faster yes, but no more reliable. BTW: The timers do get activated without the GPS input.
 
w1curtis said:
Not the 327 but the GTX 33/330. See here:
http://www8.garmin.com/pressroom/aviation/072407.html
Click to expand...
thanks, I did miss that press release.

Good stuff for us in Europe, not so much in the US. 1090 ES is only used by the airliners in the US, while in Europe there is no difference between GA and the airliners, every plane must use 1090 ES.

I am quite convinced that the upgrade will also be hardware, though. And they only mention 1090 ES transmission, so planes with the upgraded Garmin mode S boxes will be visible by planes (and ground stations) equipped with 1090 ES, and *not* by other GA planes equipped with UATs. Not so much worth investing money on this, IMHO.

Ciao, Luca
 
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