bretorey Posted June 21, 2021 Report Posted June 21, 2021 Does anyone know if the Bendix/King KA-134 will interface in any way with a Garmin GNX-375? If so, is there anyway I could get a point in the right direction as to how and through what pins. Thanks for any information that you might have that will point me in the right direction.
Vance Harral Posted June 21, 2021 Report Posted June 21, 2021 The KA-134 is an audio panel, so I'm assuming you're talking about "interfacing" audio output from the GNX-375 to it. Per the linked thread below, pins 46 and 47 of the J3751 connector on the GNX-375 carry audio output. A shop can certainly connect these pins to an input port of the KA-134, but there are two potential issues I can think of. 1) Impedance matching. I found a post that says the KA-134 presents a 500 ohm impedance to the device driving it, which is conventional, so probably no issue. But modern audio panels typically have automatic gain controls that ensure audio received from just about any device is held within a reasonable volume range. The KA-134 will not have this. Garmin keeps their installation manuals private, and I wasn't able to find the output impedance of the GNX-375. It's possible there will be a volume issue, but it's likely it will work fine with no engineering involved other than connecting the wires. 2) The KA-134 has no "unswitched audio" inputs, which IMO is a bigger deal. You'll have to connect the 375 to a switched input, likely the DME or ADF, assuming you don't have both a DME and and ADF installed in your airplane. This means it will be possible to accidentally disable audio output from the GNX-375. That arguably defeats the purpose of having audio warnings in the first place - it would bother me a lot to know a traffic or terrain warning could be lost simply because of how my audio panel powers up. I suppose you could put a placard on your glare shield that says something like TRAFFIC AND TERRAIN ALERTS REQUIRE DME SOURCE TO BE SELECTED ON AUDIO PANEL, but that seems klunky to me. Pins
bretorey Posted June 21, 2021 Author Report Posted June 21, 2021 Vance Harral, Thanks for the input sir. I will definitely look into this and hopefully it will solve the current issue I'm having.
PT20J Posted June 23, 2021 Report Posted June 23, 2021 Traffic alerts should go to an unswitched input.
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