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Com freq deocding with IFDx40?

Printed From: Avidyne
Category: Avidyne General
Forum Name: AMX240 Audio Panel
Forum Description: Topics on the Avidyne AMX240 Audio Panel
Printed Date: 13 Jul 2020 at 7:41pm
Software Version: Web Wiz Forums 12.01 -

Topic: Com freq deocding with IFDx40?
Posted By: MysticCobra
Subject: Com freq deocding with IFDx40?
Date Posted: 20 Jul 2014 at 4:11pm
In the AMX240 product brochure (see" rel="nofollow - ), there is a feature highlighted at the bottom of the second page.  The text in that box reads (emphasis mine):

Quote Optimized for use with Avidyne Integrated Flight Displays (IFDs), the AMX240 enables Com Frequency decoding and Frequency Monitoring of the two transmit and four receive channels of the IFD’s Com audio. ...  When interfaced with the AMX240, the IFD540, the IFD440 and the IFD5000 (Release 9) are able to decode the active Com frequency and display the agency name. At a glance, you know with whom you will be talking when you key your mic.

I can understand the AMX240 being required for the "monitor standby freqs" function.  However, I do not understand the IFD's dependency on the AMX240 for the Com/Nav freq decoding feature.  The IFD540 Pilot's Manual does not say anything about requiring an AMX240 for that feature (see "Cool Feature" box on p. 1-17 of Pilot Guide, here:" rel="nofollow - ):

Quote Decoded Agency Identifier
The agency (e.g. Clearance Delivery, Ground, Tower, Approach, etc) for the Active and each displayed Standby com frequency are displayed in each com frequency slot. This is a handy reminder of the agency to which you have tuned in each slot. Similarly, if the frequency displayed is a nav frequency, then the Morse code decoded identifier will be displayed and will stay displayed for as long as the IFD can decode the Morse code, which serves as a usable means to Tune-Identify-Monitor.

Did someone in the marketing department get a little overzealous with the AMX240's role in com freq decoding on the IFD's, or what?

Posted By: AviJake
Date Posted: 20 Jul 2014 at 4:48pm
We only hire overzealous folks in the marketing department!

But, you are right, there is no need for the AMX240 to be present to get this function on the IFD540.  We always decode the agency identifier for all active and standby frequencies that are displayed on the IFD540, no matter what the audio panel may be.

Steve Jacobson

Posted By: MysticCobra
Date Posted: 20 Jul 2014 at 4:50pm
Haha!  Okay, thanks for the (very quick!) clarification.

Posted By: Catani
Date Posted: 20 Jun 2016 at 3:56pm
That same excerpt in the original post also implies that the ability to monitor a standby frequency only applies to IFD com radios.  If so, the AMX240 would not be able to monitor a 430W standby com frequency in an aircraft so equipped, if the AMX240 was plug-n-play swapped with a GMA340.  Is that implication an accurate statement of the limits of AMX240 compatibility, or is it another example of marketing department exuberance?

Posted By: DavidBunin
Date Posted: 20 Jun 2016 at 4:12pm
The GNS equipment does not output standby comm audio.  There's nothing any audio panel can do about that.

Posted By: Catani
Date Posted: 20 Jun 2016 at 5:58pm
Thanks David, did not know that.  I've got one IFD440 and one 430W as a backup GPS/Com/Nav. 

Does MON1 work even if you've got both COM1 & 2 selected and active?  Just want to confirm my assumption that monitoring ATIS on MON1 does not come at the expense of audio from a Garmin COM2.

Posted By: dmtidler
Date Posted: 20 Jun 2016 at 6:52pm
I have an AMX240 coupled to an IFD540 and KX-155. I can listen to the IFD540 active comm frequency with COM1 selected, the IFD540 first standby frequency with MON1 selected, and the KX-155 active comm frequency with COM2 selected all simultaneously. Your Garmin 430W would just be in the place of my KX-155 as I understand your configuration.


Posted By: Catani
Date Posted: 21 Jun 2016 at 12:11am
Thanks dmtidler for that confirmation.

Posted By: DavidBunin
Date Posted: 24 Jun 2016 at 11:04am

If you are replacing a GNS430/GMA340 with an IFD-540/AMX240 then make sure your shop puts in the wiring to carry the Monitor audio from the IFD to the AMX.

Since the GNS unit did not have a standby monitor function, your airplane probably doesn't have that wiring.

Also, have them double-check the Alert Audio wiring while they're in the neighborhood.


Posted By: Catani
Date Posted: 24 Jun 2016 at 10:14pm
Thanks David, will do.

Posted By: AUXAIR
Date Posted: 25 Jun 2016 at 2:33pm
Good advice, since I went from GNS to IFD units, and had to go back later and have both those wires installed since they are not standard in the GNS wiring.

David E.
Cessna 182 RG II

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