Audio cable from Dynon to audio panel

[Speeddog8]

Rhino, Thank you for the correct wiring diagram. To answer a few of your questions: Your correct, the PM3000 has a function to mute the audio input and I’m familiar with that. Turns out, I don’t use it. I don’t like my music (or alerts) to be muted and that function stays inactive unless turned back on with the push of the knob, so I don’t really see a need to switch to a non-switchable input in my particular case. Earlier, when I mentioned that when I pull out the squelch knob, I hear squelch, I wasn’t referring to the intercom. I was referrring to the SL30 (Radio Static). You are correct that the intercom squelch is adjusted by the turn of the lower knob, but that’s not at issue here, and that function appears to be working fine. What really confuses me here is that the SL30 and PM3000 have been working fine for years until I integrated the intercom inputs into the HDX. That said, I did also integrate the SL30 into the HDX as well to provide com and nav data to each display (But those functions appear to be working perfectly). I have control of the com frequencies thru the HDX and nav frequencies and data are being fed to the HDX HSI.

 

[Speeddog8]

I’m beginning to think that the intercom is not the problem. Something is causing the SL30 to break squelch. What can do this? Is it possible for high amp draw after engine start can cause this? The reason I say that is because the problem goes away after a few minutes of flying the airplane (Battery recharged after the start). I’m spitballing here….
I’ll get out to the airport tomorrow to see if I can narrow down what its doing. It’s a composite airplane, so its somewhat typical to have more audio and RF related issues than with metal construction.

 

[Rhino]

What intercom inputs did you integrate into the HDX? It doesn't receive any audio.

 

[Rhino]

My next step would be to simply remove the HDX from the equation and disconnect it. You should be able to use the radio with just the intercom. If your problem goes away, it's likely you have a wiring issue related to the HDX interconnect, probably something shorting to ground. Disconnecting the HDX doesn't eliminate the wiring issue entirely though, because the cable is still connected, and the problem could be in the cable. It does increase the odds though.

 

[Speeddog8]

What intercom inputs did you integrate into the HDX? It doesn't receive any audio.

I meant to say outputs from the HDX to the intercom. The alerts.

 

[Speeddog8]

My next step would be to simply remove the HDX from the equation and disconnect it. You should be able to use the radio with just the intercom. If your problem goes away, it's likely you have a wiring issue related to the HDX interconnect, probably something shorting to ground. Disconnecting the HDX doesn't eliminate the wiring issue entirely though, because the cable is still connected, and the problem could be in the cable. It does increase the odds though.

Thanks Rino. I’ll give that a try. BTW, I saw a note on the PM3000 wiring diagram that said:
Pin 18 is music “floating low”. I realize the word “low” is a term for ground, but what does floating mean?

 

[Speeddog8]

Rhino, My apologies. I know I’m wearing you out, but while I have you, should I consider disconnecting the audio cable shield from the Dynon ground (pin-30) since it is already connected to ground at the intercom (to avoid a ground loop)? Also, if I disconnect it from the Dynon, should I then run a ground wire from pin-30 to my main ground bus, or leave pin 30 empty? Looking for a suggestion on that issue. Thanks.

 

[Rhino]

Grounds are usually connected to earth ground, or, in the case of an aircraft or vehicle, chassis ground. Literally speaking, a floating ground doesn't connect to those things. It merely acts as a shield against spurious noise. However, many people, including electronics vendors, play a bit loose with the term. Pin 18 connects to all the shields in the wiring, so it appears to act like a floating ground. But if you look at pin 1, you'll see that all the shields are tied to ground, so it isn't truly floating. However, many of the audio connections use the shield grounds for low, so PS Engineering is actually calling that a floating low for audio purposes, not a floating ground. Like I said, many folks are flexible with the term. It shouldn't be a concern for you though.

You can leave pin 30 on the HDX disconnected, though I doubt this is your problem. Issues there usually involve induced system noise, such as alternator whine or buzzing, or when you transmit on a radio, transponder, etc. PS Engineering recommends only grounding at the intercom or com panel, but it isn't a hard and fast rule, and it usually causes no problems. But if you look at page 16-9 of the current Skyview installation manual, you'll see Dynon agrees with this practice.

 

[Rhino]

Rhino, My apologies. I know I’m wearing you out, but while I have you, should I consider disconnecting the audio cable shield from the Dynon ground (pin-30) since it is already connected to ground at the intercom (to avoid a ground loop)? Also, if I disconnect it from the Dynon, should I then run a ground wire from pin-30 to my main ground bus, or leave pin 30 empty? Looking for a suggestion on that issue. Thanks.

Leave it empty. The HDX is already grounded on pins 21 and 22 of the D37 connector.

 

[Speeddog8]

Rhino, You’ve given me a lot of homework, but I’m 90% certain my intercom is a 4-place model, not six. I’ll have to verify the specific model. I have three headphone jacks installed in the airplane as I have a small jump seat in the back. The music input from this intercom used to go to a music input mini- jack that I’d plug my iphone into for music, but now that I have Bluetooth headsets, I removed that jack and instead connected those same music input wires to the Dynon 37-Pin connector including the shield for ground. I’m getting the audio alerts from the Dynon just fine. Even without the engine running, I have a bit of low level hum and clicking in my headset. I need to do a bit more testing, but in the hangar tonight, the squelch issue didn’t occur. I can pull the SL30 squelch knob out and got squelch, so I’m inclined to say that the problem squelch issue only occurred the other day when the engine was running. Also, to answer you initial question. Yes, I’m getting full static from the radio, not system noise (aside from what I just described above). While installing the HDX, I plugged in and listened numerous times with my headsets along the way and never encountered this squelch issue, so I’m inclined to say that the problem only occurs with the engine running. I’ll get that tested shortly. What do you mean by “aux headphone jack”? Btw, thank you for your response. I really do appreciate it!

UPDATE: So, ultimately this matter was resolved. I’ve been flying my plane for years with the SL30 and never had any significant issue with squelch break. I took the radio to an avionics shop about an hours drive away. He connected it to his bench equipment and within minutes determined that I had inadvertently turned the Nav ID function on and was also monitoring the standby nav frequency (which doesn’t cancel when the radio is powered off and on). Regardless, it was “operator error” of the SL30. Remember the old saying, “Ya gotta be smarter than the equipment you’re trying to operate”. Apparently, I failed miserably. Hard to believe I’ve flown the SL30 for so many years and never run into this problem before. Probably because I rarely use the Nav functions of the radio.

 

[Speeddog8]

But here’s another problem, and really my final, known problem with my installation. With the engine not running, If I turn EVERYTHING off. except for the two HDX screens and the intercom, I hear a faint clicking noise and a faint buzzing noise. If I turn the HDX screens off, the noise goes away. If I turn only one of the screens off, the nose remains, but seems a bit less prominent. Would noise filters added to each of the 37 Pin connectors at each screen, likely resolve this issue? Anybody had this problem? In flight, I can barely hear this noise, but I’d love to get rid of it, if possible.

 

[Rhino]

A faint clicking sound from the HDX is normal, but you don't necessarily hear that over your audio lines. However, you can get clicking over audio sometimes when the dual watch function is active on a radio. Since radios get power from the intercom, you can disconnect them to isolate, and confirm they are or are not the source of the clicking. But if dual watch is the source, I don't think you can do anything about that. You'd need to ask Dynon.

Without knowing where the buzz is coming from, it's impossible to say if the filter would work. But since power comes in to the Skyview on both pins 1 and 20, you'd need four filters.