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  #1  
Old 03-09-2020, 12:45 PM
jgbmo jgbmo is offline
 
Join Date: Jan 2016
Location: Higbee, MO
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Default I'm installing my own avionics - question

I've got a PS Engineering PM2000 intercom, a King KMA24 audio panel, a Garmin GNC355 gps/comm, and a Garmin SL60 gps/comm that I'm installing in the RV7 I'm building. All of the radios are used except for the GNC355. The intercom works fine between the pilot and copilot, PTT works, too. I can hear audio coming back through the audio panel and intercom from the gps/comm radios and it seems fine. The problem is that when I use the PTT, instead of my voice being transmitted I get a tone (200 hz, I'm guessing) and no intelligible voice. I suspect I have a wiring screw-up on the mic side, but am unsure where to look.

Any help is appreciated!
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  #2  
Old 03-09-2020, 01:12 PM
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fl-mike fl-mike is online now
 
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Funny tone on one or both radios when PTT? (selected)
Assuming you have the correct radio selected for xmit on the KMA24, I'm going to guess that the audio out of the KMA24 to the radios is either on the wrong pin (at one or both ends), not connected, broken wire, or you have COMM 1 and 2 audio swapped.
Sounds like you are keying an open wire on the radio audio input.
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Last edited by fl-mike : 03-09-2020 at 05:14 PM. Reason: had the intercom and audio panel numbers reversed
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  #3  
Old 03-09-2020, 01:15 PM
jgbmo jgbmo is offline
 
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Both of the radios transmit the same way (with the tone and no voice). I wired them the same way into the audio panel, so I'm pretty sure I connected pins the wrong way at the audio panel--or from the mic side of the intercom to the audio panel. Things get a bit confusing since King, Garmin, and PS Engineering use slightly different terminology and logic in their wiring diagrams.
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  #4  
Old 03-09-2020, 02:08 PM
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rocketbob rocketbob is offline
 
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Did you connect the transmit interlock lines between the two comm radios?
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  #5  
Old 03-09-2020, 04:32 PM
jgbmo jgbmo is offline
 
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I'm afraid I don't know what "transmit interlock lines" are? Nothing related to a flux capacitor, I trust ;-)
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  #6  
Old 03-09-2020, 08:18 PM
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fl-mike fl-mike is online now
 
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Based on install manuals I found on the web, I think this is the wiring between the audio for the intercom, audio panel, and radios. (does not include power, etc. Just the audio and PTT stuff)
See if this matches your wiring diagram or wire list.

oops, Add KMA24 pin "1" to the the intercom ground row. (KMA24 has a power ground, "speaker" ground, and and "everything else" ground.)
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  #7  
Old 03-09-2020, 09:39 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by jgbmo View Post
I'm afraid I don't know what "transmit interlock lines" are? Nothing related to a flux capacitor, I trust ;-)
A transmit interlock is a wire from PTT for #1 to an interlock or mute input on #2, and vice versa. So if the antennas are close together you won’t get annoying feed thru on the radio not in use. To test if you need this, just turn off #2 and transmit on #1, see the the problem goes away. Not all radios have this input.
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  #8  
Old 03-09-2020, 10:39 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by fl-mike View Post
Based on install manuals I found on the web, I think this is the wiring between the audio for the intercom, audio panel, and radios. (does not include power, etc. Just the audio and PTT stuff)
See if this matches your wiring diagram or wire list.

oops, Add KMA24 pin "1" to the the intercom ground row. (KMA24 has a power ground, "speaker" ground, and and "everything else" ground.)
Sorry, but I know nothing about the KMA 24 and am surprised it has comm audio out and audio in.

From what I gahter from your chart, KMA audio out should go to Mic hi on the radios and audio in should go to the Phones hi pin on the radios. Need to be carefull here, as many radios have both headphone pins and speaker pins. You want the 600 ohm headphone pins. The radios may also have an audio in pin that is designed for high impedence sources such as stall or traffic warnings. Mic output (i.e. Audio Out) needs to go to a pin called mic or mic hi on the radio, not something called audio. At least for modern Garmin radios. This is possibly your problem.

You will need to review the KMA manual to understand what direction In and Out refer to, as I may have it backwards. I am guessing here on what they mean. I assumed they meant in or out of the KMA.

You;ll want to tie the two phone lo's together with the KMA other ground and tie the two mic lo's to the KMA other ground as well. Not really sure if this is the best config for the KMA. Maybe Bob Turner can give guidance on that. Again, I have no experience with the KMA so can't advice well on ground ties. Most modern audio panels tie all of the lo's on a common ground bus in the a/p.
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Last edited by lr172 : 03-09-2020 at 11:16 PM.
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  #9  
Old 03-10-2020, 07:04 AM
jgbmo jgbmo is offline
 
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Location: Higbee, MO
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Thank you to all! I'm going to go through my wiring with the chart and info you all have provided to check after breakfast this morning. Regarding the interlock, I think the audio panel provides that functionality. Regardless, I get the tone even if only one radio is installed in its rack, so I doubt that's a problem--but I'll check it out.

Thank you all!
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  #10  
Old 03-10-2020, 09:54 AM
John Tierney John Tierney is offline
 
Join Date: Jan 2006
Location: Vonore, TN
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Default Headset Jacks

Also check that you PTT is correctly wired at your microphone jack for the headsets, grounding the tip to the barrel when pressed.

I found this PS Engineering presentation helpful, but I don't find it on the PS Engineering website any more:
https://slideplayer.com/slide/2364675/
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