intercom vox over-ride PTT - PFM?

[Salty]

My Nanchang has a nice feature where you can hit a second PTT button to over ride the Vox and talk over the intercom without vox. It's nice in a loud cockpit because you can basically turn the squelch so that Vox is off and not have the annoying hissing, and use the button when you want to talk.

But, I can't figure how how the heck it's wired up to work like it does. I have a SPA-400 intercom and the feature clearly works, but there's no indication on the intercoms wiring diagram how you would make it work that way. I have no idea where the button is wired up to. Trying to understand how it works. There are 3 wires coming off the switch, 1 is to ground, the other two, I have no idea where they go.

 

[AV8R_87]

It might be a feature of your actual radio. The GNC250XL had a built-in PTT ICS. What radio do you have in the plane?

 

[dmspilot]

Maybe the switch tricks the intercom into believing you're transmitting on the radio, but simultaneously disconnects the mic audio from the radio. I can think of other variations on that theme.

 

[AV8R_87]

The only problem with that scheme is that sidetone is (usually) generated inside the radio. So not keying the radio won't give you audio in the headphones.

 

[Salty]

It might be a feature of your actual radio. The GNC250XL had a built-in PTT ICS. What radio do you have in the plane?

BK KY 96A. I'll check out it's capabilities.

 

[AV8R_87]

Yep, radio has intercom feature.