AXP340/322 ADS-B Transponder - AXP340 discrete air/ground switch

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AXP340 discrete air/ground switch

Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: https://avidynelive.com/forum_posts.asp?TID=464
Printed Date: 26 Mar 2026 at 2:13pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com

Topic: AXP340 discrete air/ground switch

Posted By: jimelliott
Subject: AXP340 discrete air/ground switch
Date Posted: 20 Nov 2014 at 10:30am

I saw this in an earlier (I think) IFD540 IM.

For those installations that use a combined IFD540 – AXP340 Mode S ADS-B transponder, the on-ground/in-air discrete signal wire may need to be added from the IFD540 tray to the

AXP340 tray as identified in Section 6.15.

I didn't see this paragraph in the current 540 IM.

Is there a way for the 340 to automatically switch from ground to air mode other than a squat switch? I was hoping I could get a signal from the 540 to do that function. Maybe based on ground speed?

Jim

N2247X

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Jim Elliott

Replies:

Posted By: AviJake
Date Posted: 20 Nov 2014 at 10:34am

Jim,

Standby up to a few days on that answer. There is some internal confusion and some of the folks who can help answer this with complete certainty are away on travel.

There is a air/ground output discrete of the IFD540. That was intended to be used for exactly that purpose (e.g. a device can use that output discrete to toggle a ground/air transition instead of needing a squat switch). I need to make sure that was implemented correctly across the board.

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Steve Jacobson
sjacobson@avidyne.com

Posted By: Gring
Date Posted: 20 Nov 2014 at 11:19am

I can tell you from experience that I flew with another AviLive user with dual IFD540s and the AXP340 transponder. His automatically switched from GND mode to ALT mode and was using the IFD540 to make that happen rather than a squat switch.

My installation powers up on ALT mode all the time, so I must not have some of that special wiring because our software configuration settings were the same.

Posted By: tony
Date Posted: 20 Nov 2014 at 2:43pm

The installation manual shows P1001 pin 8 as a weight on wheels output. On page 175 the manual shows this signal interfaced to the transponder as a squat switch. My question is, can I parallel the outputs? Is the output a dry contact? In other words can I run pin 8 from each IFD to the same pin on the transponder?

Posted By: jimelliott
Date Posted: 20 Nov 2014 at 8:16pm

Great feedback. Thanks guys!

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Jim Elliott

Posted By: jimelliott
Date Posted: 20 Nov 2014 at 8:30pm

With information from Tony's post I found this in the IFD540 IM Table 54 regarding ADS-B transponder output.

Connect the appropriate input pin on the AXP340 with the

IFD5XX P1001 Pin 8 in order to get automatic on-ground / in-air

mode transition.

I will be sure to share this with my installer.

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Jim Elliott