SV-INTERCOM-2S unmuted audio issue

[Lanceturk]

I have just completed an installation of a SV-INTERCOM-2S.
Everything works except when I connect an iPad (on or off) to the Skyview audio inputs, the unit mutes the music. It will even mute with just the cable in free air at times. The audio from the iPad is working correct.
Anyone else experienced this?
Thanks
Lance

 

[dynonsupport]

Lance,
That's by design. Audio coming in from the radio or EFIS is supposed to mute the music as these are priority inputs. The SkyView inputs are differential inputs, so if you have wired them with a common ground, or have left them ungrounded, the system is going to "hear" noise and mute the music. Free hanging wires act as antennas and pick up noise too. Is your iPad plugged into a charger while this is happening?

Technically, using the SkyView inputs for an iPad is not a supported configuration, but we'll see what we can do. First and foremost, does the iPad audio work correctly in the headset when it outputs audio?

 

[Lanceturk]

Thanks for your reply. I got rid of my PS Engineering PM3000 intercom because I needed the additional music inputs, so I really hope we can figure this out!

I have wired three conductor shielded audio cable as per install directions:
Pin 6: connects to iPad headset out (R).
Pin 19: connects to iPad headset out (L).
Pin 20: connects to iPad headset common (cable shield).
Audio from iPad comes through just fine. But when iPad audio stops, the mute of the 'music in' channels remains active - as if there is some signal present the mute function is picking up. Note that I do not 'hear' any signal. In fact, even if I shut off the iPad, the mute remains. Only by unplugging does the mute become inactive - and as mentioned occasionally I can touch the cable mini jack and cause mute to activate-again I cannot hear anything. It seems ultra-sensitive. Note that I am a EE so can talk technical.

What voltage level and impedance are the Skyview inputs looking for?
Do I need to add series capacitors to block any possible DC? Should I add a load resistor between diff. input (such as 330 ohm between pin 6 and 20?

This is the only thing preventing returning aircraft to service so your expertise is greatly appreciated.

.

 

[Lanceturk]

One more thing- your install says install twisted pairs but for a true differential input you would need a high and low for each channel. But there's only one common low (pin 20) which technically defeats a true diff input benefit. Did I miss something ? Is there another low somewhere?

 

[mrdaud]

LanceTurk - one other thing to consider is a separate summing module for all non-priority inputs. This effectively eliminates any common "low" or ground issues. There are several on the market, but the one I use in my aircraft is sold by Flight Data Systems and is the AP-60. http://www.fdatasystems.com/ap-60-audio-mixer/ Cost is moderate at only $89. I have had no issues with this set-up.

 

[dynonsupport]

The L and R channel share a common ground point, which is pretty standard in audio given they are generally sourced from the same device. Each channel is differential against pin 20, instead of the aircraft ground.

As for when it mutes... This is a sum of voltages on the EFIS, Radio 1, Radio 2, and Non-muting inputs. All of these inputs are AC coupled. There is no need for you to create a DC block.

The gain on the EFIS inputs are 1/4 the gain of the Music input, as music is generally 3V and the EFIS is 12V. So the EFIS inputs should be pretty insensitive in comparison. In a quick glance, it should take about 1.2V peak on the EFIS to trigger the music to mute. Note that if you are running the intercom on less than 10V this drifts some. Anything above 10V is stable.

This makes me wonder if the audio triggering the muting is actually on one of the other inputs. It could be infrasonic. Does it still mute if you disconnect the radios and anything else? Does it mute if the iPad does not have anything plugged into the charging connector?

 

[Lanceturk]

Thanks for that detail. I have shut down all the trigger inputs (basically just my single Navcom) and the problem remained. Today I did some more testing. I took an older iPod and used that instead of the iPad as a source into the Skyview dif inputs. This seemed to eliminate the triggering issue. I can only conclude there is some noise I cannot hear being produced by the iPad (Ive tested both an iPad mini and an iPad Air). In fact at one point I thought I could hear some slight 'computer' type noise in the headsets when changing iPad screens etc. ( note: no charger connected).
So now I've given up on the Skyview inputs. I have now connected the iPad left and right outputs ( summed with simple resistors) to the single audio input - pin 17 and referenced the iPad ground to pin one. This seems to be working quite well.
Next step will be to fly it... Wish me luck. I'll post my results.
Thanks,
Lance.

 

[Lanceturk]

I do have one additional question for Dynon...
Should the unused inputs be tied to respective ground(s) such as Radio 2 (pin 7) and Aux muting audio in (pin 4) and Skyview (pins 6 and 19)?

 

[vlittle]

I have looked at similar issues before. It might be wortih trying the following: Connect the iPad shield to your audio ground at the intercom, then the intercom common (pin 20) to the same ground.

This provides a low impedance ground for the iPad. Otherwise, noise energy in the shield will be have to flow into the common pin, which I presume to have a non-trivial input impedance and will therefore convert longitudial currents in the shield to noise.

Vern

 

[Lanceturk]

As an update, I have spent several days conducting numerous tests. The tests were intended to determine what is effective and what isn't in terms of a 'fix' to minimize the 'try this and that', which gets expensive and time consuming and may not result in a fix

My opinion is that the high power narrow XPNDR pulses are getting into most of the sensitive avionics I have onboard. BTW I fly a Glasair so don't have the benefit of a 'faraday cage'.
I measured RF generated audio pulses and they are between 50usec to 130usec. Very small. The problem is they can be heard as a pop/tick. Here are a few things I tried and the results:
1. Took intercom out of panel and wired directly to a small 12v battery and to a headphone via a single jack. Walked around airplane with this 'portable' set up. Result: noise present and increased when closer to XPDR antenna and vice versa. Predictable.


2. Took noise cancelling  Bose headset out of aircraft and with noise cancelling on then walked around antenna. Same Result as intercom.

Conclusion: need to move antenna as far aft as practical to hopefully reduce coupling with all the wires/coaxes/boxes/etc. etc. Need to make sure coax is good RG400 and there are no leaks.
NOTE: Heard that Cirrus found this as an effective fix to their 'plastic' airplanes too.

3. The most irritating issue is the music muting when the SV 'hears a 'tick'. As an interim bandaid, I Designed and installed a roll-off circuit which is inserted between my 'radio audio output' and the intercoms 'radio input'. This reduced the 'tick' amplitude enough to stop triggering the intercom 'mute' function (which annoyingly interrupts the music about every two seconds!). Note that this frequency roll-off does make the Navcom sound more muffled/bass but I kind of like it as it also cuts out a lot of static.
I bet DYNON engineers could change the mute trigger circuit slightly to not respond to these very narrow audio pulses. That would at least allow music to continue to play.
I would be very happy to work with them. My guess is this problem will be very chronic as more and more ADS-B installs are made.

 

[jakej]

The 'joys' of plastic airframes  ;D

FWIW - I don't have any issues with the Dynon Txpdr (261) & ADSB out but then again  I always use RG400 & keep the antennas, particularly the Txpdr, as far apart as possible to reduce the coupling also.  Seems to work so far on 20 + compositre airframes I've wired, just as well as I don't have your expertise to build 'tricky' gadjets for a 'workaround'. 

Jake J
Glasair IIS FT in Oz.

 

[vlittle]

When I was chasing audio system noise in my Rocket, I could hear the transponder ticks in my headset. Turns out that I could hear this noise even with the headset unplugged! The solution was to take the aircraft outside.

The ES pulses from the transponder were the culprit. Inside a metal hangar these pulses bounce around and are demodulated by anything electronic, including circuitry in ANR headsets, even when unpowered.

Maybe this is a clue...

Vern

 

[Lanceturk]

Vern, yes I certainly agree that a metal hangar will exacerbate the issue. It does do it outside as well, but to be honest, I don't know how much improvement there is outside. I'll check that.

Jake, as mentioned I am going to try moving XPNDR antenna aft ( this is farther away from radio stack but uinfortunately closer to navcom antenna - IMO the noise is not coupling through these antennas though)

I never had ANY issue with the original
AT150 - it's probably less 'power out' though...

 

[jakej]

Vern, Testing & finding faults while in the hangar is a common issue, hopefully more people read these comments.

Lance - FWIW my original install had the Txpdr (Apollo SL70) antenna (fully internal) way back aft in the fuselage, now with the Dynon 261 it is internal just aft of thge firewall with no issues in either position. Btw - both com antennas are internal copper strip dipoles, one just aft of the baggage area & the other in the leading edge of the vertical fin. Nav antenna is in the leading edge of the horizontal stabiliser.

 

[Lanceturk]

All,
Flew airplane today. It is less 'ticky' when airborne. My roll-off circuit reduces tick amplitude enough to not trigger intercom mute function. The second best solution would be to modify the intercom mute trigger circuit. DYNON - would you be willing to let me try doing this on my unit? Just need a schematic - will sign NDA etc.
The single best solution would be to get rid of interference.

FWIW, there was a Cessna 185 on the radio in the pattern and his transmission was FULL of the ticking noise. He has a ADS-B system ( I know because I could see his data on my traffic display ). Guess I'm not the only one with ADS-B issues...

Jake - what is the shape of your XPDR antenna ground plane?

 

[jakej]

Lance - same one as I fitted 23 years ago approx 12" diameter

 

[Dynon]

All,
Flew airplane today. It is less 'ticky' when airborne. My roll-off circuit reduces tick amplitude enough to not trigger intercom mute function. The second best solution would be to modify the intercom mute trigger circuit. DYNON - would you be willing to let me try doing this on my unit? Just need a schematic - will sign NDA etc.
The single best solution would be to get rid of interference.

Our products aren't designed to be field-modified, and so the generic answer here is that we're not able to offer schematics and other design documentation for those purposes. That said, we'd like to see how we can help. Can you send an email to our support team with a link to this thread to follow-up? We'll get you in touch with some of our engineering and support management.

 

[Lanceturk]

Thanks, I appreciate and understand you position. I will contact your support group to go forward.
Regards,
Lance Turk

 

[Lanceturk]

DYNON SUPPORT:
Per Dynon Forum recommendation, I sent email directly to Support. This was several weeks ago. I have received no reply.
Is this normal?

 

[Dynon]

It isn't. We did have a few days of our support system not working quite right, although we thought we thought we caught all of those cases. Looking into this...