What this be for???

[Glen Davis]

This mini jack connector in the panel is labeled “comm 2 interrupt “.  Anyone have one like this and can explain what it’s for?

[Marauder]

This mini jack connector in the panel is labeled “comm 2 interrupt “.  Anyone have one like this and can explain what it’s for?

It’s a port to plug a handheld radio into. It will attach your portable handheld to one of the aircraft’s antenna to give you better range on your handheld.


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[BDPetersen]

You would think with all the English Majors in the world a more descriptive nomenclature could have been derived. 

[M20F]

I wish my girl had one of these…..

[KLRDMD]

11 hours ago, Marauder said:

It’s a port to plug a handheld radio into. It will attach your portable handheld to one of the aircraft’s antenna to give you better range on your handheld.

I've been told you must turn COM #2 OFF beofe using this port or you will fry your #2 COM.

[PT20J]

Sharing antennas can cause all sorts of issues. That's why each of your com radios has it's own antenna. If I wanted an external antenna for a handheld, I'd put a dedicated "bent whip" VHF antenna on the belly.

[EricJ]

1 hour ago, KLRDMD said:

I've been told you must turn COM #2 OFF beofe using this port or you will fry your #2 COM.

That's why it should be an "interrupt" switch.   My airplane has one of a different type and I verified that it's a switch instead of a transformer couple.   In other words, inserting a plug into the jack disconnects the Comm 2 radio from the antenna and attaches the plug instead.   This isolates the Comm 2 receiver circuit from the handheld transmitter to prevent damaging the Comm 2 receiver with the transmit power from the handheld.

[Marauder]

That's why it should be an "interrupt" switch.   My airplane has one of a different type and I verified that it's a switch instead of a transformer couple.   In other words, inserting a plug into the jack disconnects the Comm 2 radio from the antenna and attaches the plug instead.   This isolates the Comm 2 receiver circuit from the handheld transmitter to prevent damaging the Comm 2 receiver with the transmit power from the handheld.

Exactly. That is what the old KX99 port I had did. That is until it failed




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[EricJ]

3 minutes ago, Marauder said:

Exactly. That is what the old KX99 port I had did. That is until it failed




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Yes. thats what I have.   It might be what's behind the jack in the OP's pic, too.

 

[Pinecone]

The problem with Com 2 would be if you transmitted on it with the handheld plugged in.

A smart way to do this would be to route Com 2 to a dummy load (resistor) when the hand held is plugged in to avoid damage.

[Fly Boomer]

9 hours ago, Pinecone said:

A smart way to do this would be to route Com 2 to a dummy load (resistor) when the hand held is plugged in to avoid damage.

Back in the day, we used a light bulb of appropriate wattage.

[EricJ]

So to clarify, there are two concerns with using one of these or something similar:

1.  Older radios, or any radio without transmit protection, can damage the Power Amplifier if transmitting wihout a load, in other words without an antenna connected.   Many newer radios aren't sensitive to this, but it's always good to check before trying it.

2.  Most receivers, even many newer ones, are sensitive to high-power inputs so shouldn't have another independent transmitter connected to the same antenna.   This works within a radio because the push-to-talk switch disconnects or isolates the receiver before turning on the Power Amplifier to transmit.   The KX99 or similar devices disconnect the COM to facilitate this and also to allow all of the handheld TX power to go to the antenna.

So, yes, it's a good idea to turn COM2 off if something like this is used that is connected to COM2, just to eliminate the possibility of potential damage to the PA if the transmitter gets keyed somehow.