Mic ground to audio panel

I can find many examples of how to wire the push to talk switch to a radio (through the Mic jack).

I need to wire radios to an audio panel. The radios have three pins; "Mic," "Mic return," and "Mic key." The audio panel has two pins to connect to the radios; "Mic" and "Mic key." The audio panel has three pins to connect to the Mic jacks; "Mic," "Mic return," and "Mic key." The diagram describing audio panel to Mic jack connection is exactly the same as a standard radio to Mic jack, so no problem.

The problem is connecting the radios to the audio panel. The audio panel diagram shows only two wires; "Mic" and "Mic key." The radio diagram shows three wires; "Mic," "Mic return," and "Mic key." Right now I am planning to connect the "Mic return" from the radio to the shield ground on the audio panel. Anyone know if this is correct?

Pat

Signal and Key PTT

Hi,

My understanding is:

Mic & Mic Return wires are the signal and ground return for the actual microphone, ie. the signal that gets amplified.

The Mic Key PTT is a control signal which is ground activated - ie. when the key wire is connected to ground, the mic is 'active'. With a headset PTT - the button connects the Mic Key line to the Mic return line. With a remote PTT (stick / panel) the button connects Mic Key to Ground.

We have followed the single point / cabled ground principle, so all paths come back to a single 'ground tab' anyway.

Hope that makes sense....

Carl

models?

Pat,

Which audio panel and which radio do you have?

gil in Tucson

az_gila said:

Which audio panel and which radio do you have?

Click to expand...

Gil,

I have a Garmin GMA 340 audio panel, and I am connecting an SL 30 and a GNC 300XL to it.

Pat

Audio Panel <-> Radio

Hi Pat,

Sorry - I miss read the original question - let me try again.....

An example GMA340 to radio connections.


On our SL30 (as supplied by Stark)
DB15-SL30:7 Mic Ground is unconnected (I assume gets internal ground)

GNC300XL uses pins
DB26-300XL-J102:2 - Mic High
DB26-300XL-J102:3 - Mic Low / Return
DB26-300XL-J102:4 - Mic Key
DB26-300XL-J102:5 - Com High
DB26-200XL-J102:6 - Com Low / Return

Pin 3 is tied to ground - as per page 31 of the GNC300 Install manaual (see Mike Stewart Garmin manual page http://www2.mstewart.net:8080/Downloads/howtogetagarminmanual.htm )

Does that help a bit more?

Carl

Connections

Hi Pat...

...this should be easy enough...:^)

The 340 Audio panel needs mic and PTT connections to the radios.

Assume the GNC300 is COM1

340-J1-pin11 "Comm 1 Mic" goes to GNC-J2-pin2 "Mic Audio HI"
340-J1-pin12 "Comm 1 Key Negative" goes to GNC-J2-pin4 "Mic Key"

This connection should be a shielded pair, with the shield connected to audio ground at the audio panel end only.

Looks like GNC-J2-pin3 "Mic Audio Lo" is grounded locally at the radio end ...this is per Fig 1-4, note 5 of the GNC300 installation manual.

Note that the 340 audio panel requires that all of the headset jacks be isolated from the airframe location they are mounted at...

Hope this helps.... Gil A

Carl and Gil,

Thanks a lot for the replies. Trying to decipher these manuals makes my head hurt; there is no standardization even within the same manual. Bus high/bus low, signal/ground, in/out, and audio high/audio low are apparently all used interchangibly depending on the state of the tide and mood of the tech writer.

I am using the SL 30 as com 1 and the GNC 300XL as com 2. The pin numbers you have indicated match the ones I am using exactly, so at least that part is clear.

Unfortunately, it gets murkier from there. Let's start with the SL 30. The SL 30 installation manual which was packed with my radio (dated August 2003) has a "typical audio panel connections" diagram on page 19. This shows 'Mic 1' (pin 8) connected to the audio panel 'Com Mic Audio' pin, 'Mic Ground' (pin 7) connected to the audio panel ground block and wire shields, and 'Tx Key' (pin 4) connected to the audio panel 'Com Mic Key' pin. This is the way I have the radio wired right now (I haven't put any power to it yet - I want to get this cleared up first!)

My GMA 340 was not shipped with an installation manual, so I am using revision L, which I obtained on-line. This manual pretends that com 1, com 2 and com 3 have no 'Mic Return' pins, and does not mention them in any way that I can find.

The GNC 300XL is even worse. There are several versions of the manual floating about. Since revision E was packed with my radio, I would naturally prefer to use it, although I am open to other input. The page numbers and figure labels in revision E are completely different than the ones you have cited, so no direct comparison is possible. Looking at the manual downloaded from Mike Stewart's site (revision J) on pages 30 and 31 I can see the notes you have indicated. However, the diagram and note 5 do not really match very well. The diagram shows pin 3 (which is not even labeled) connected to the mic shield and then to the ground of the mic jack - shield connected at both ends! Note 5 (which specifically addresses emergency use of the com in the 300XL - a feature which I will not be using) shows pin 3 connected directly to ground, while the mic jack ground is connected to the shield which is then grounded at the audio panel. The equivalent note in my manual is note 9 on page 5-10, which shows a seperate wire for the mic ground which is connected to 'Mic Audio Lo' (pin 3), the emergency mic jack ground, and the audio panel (this diagram also shows shields grounded at both ends). Once again, I have connected pin 3 to the audio panel ground block and wire shields, while the radio end of the shield is unconnected.

Thanks again for the input, and if anyone can throw any light on this, please let me know,

Pat

Revisions...

4kilo said:

Carl and Gil,

Thanks a lot for the replies. .....

Once again, I have connected pin 3 to the audio panel ground block and wire shields, while the radio end of the shield is unconnected.

Thanks again for the input, and if anyone can throw any light on this, please let me know,

Pat

Click to expand...

Pat ... the general standard is to do what you mentioned above.

Ground all of the shields at one end only, and if you have an audio panel, ground the shields at the audio panel.

Unless the Installation Manual says otherwise...

Sorry to hear the confusion over installation manuals... are they tied in any way to the equipeent revision, which is usually marked on the avionics?

For reference I was looking at 340 IM rev J and GNC300 IM also at Rev J

Note 5 (which specifically addresses emergency use of the com in the 300XL - a feature which I will not be using) shows pin 3 connected directly to ground, while the mic jack ground is connected to the shield which is then grounded at the audio panel.

This note just shows extra wiring for the emergency jacks (a good feature to have), but remember the mic jack ground you refer to above is not airframe ground... all jacks are isolated...

hope this helps... gil A

Gil,

It sounds like I do have things wired correctly, I was just looking for some reassurance before the smoke test!

By the way, the reason I am not using the emergency jack feature of the GNC 300XL is that com 1 is the SL 30, and I have an emergency reversion system set up on that.

Thanks again for the info,

Pat

Extra jacks...

4kilo said:

Gil,

It sounds like I do have things wired correctly, I was just looking for some reassurance before the smoke test!

By the way, the reason I am not using the emergency jack feature of the GNC 300XL is that com 1 is the SL 30, and I have an emergency reversion system set up on that.

Thanks again for the info,

Pat

Click to expand...

Pat.... correct, you only need one emergency system on comm 1...

A lot of folks don't put it it in, but for the cost of 2 jacks, you will have communications when the intercom and/or the audio panel go belly-up...

gil A