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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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 Posted: Sun Jun 28, 2015 9:24 am Post subject: Audio Noise |
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Below is a quote from a RV-12 builder in Australia, as posted on VansAirforce:
| Quote: | I've had a constant `bzzt....bzzt...bzzt' sound in my headset repeated at exactly one second intervals. Both pilot and co-pilot sides were affected. The sound level stayed constant despite adjusting the intercom squelch and volume knobs, and was unaffected by the transponder, radio, autopilot or lights. At first I thought the sounds were related to the flashing warning signs on the Dynon, but later realised they were exactly timed to the digital clock on the display. The noise would start as soon as the boot sequence got to `starting network manager'. If I unplugged the GPS antenna from the AV5000 module so that the system couldn't pick up the time signal from the satellites, the clock would not appear and neither would the noise. Dynon initially thought it might be related to the transponder, but neither disconnecting the transponder, the EMS, or anything else seemed to make any difference. If the clock was active, so was the noise. The only way to get rid of it was to disconnect the GPS antenna, which wasn't really a good solution. However, flying with the noise wasn't an option either as it was as irritating as a dripping tap.
However, I got lucky this afternoon when a local electronics guru happened to be at the field. He spent a couple of hours trouble-shooting the system, checking the Skyview settings, the radio, tracing the wiring diagram, pulling pins, etc, until he eventually discovered that the noise was apparently being generated by interference between the music jack wires and the tunnel harness, which runs to the ADAHRS mounted in the tail cone. When the GPS antenna was connected, it appears that EMF generated in the network cable was being fed into the audio wires that run close to the cable in the tunnel, and was therefore audible in the headsets. Disconnecting the two audio wires fixed the problem. It was a simple solution, but tracking down the cause has been a very frustrating exercise. Glad it's been fixed now. |
The length of the shared wire harness is five feet. We will never know the true cause. But is it more likely that the audio interference was due to the proximity of wires, or due to the fact that the stereo music input jack was grounded locally to the airframe (without isolating washers) instead of having a dedicated ground wire running back to the instrument panel ground?
Joe
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Joe Gores |
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ceengland7(at)gmail.com
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| Posted: Sun Jun 28, 2015 1:04 pm Post subject: Audio Noise |
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On 6/28/2015 12:24 PM, user9253 wrote:
| Quote: |
Below is a quote from a RV-12 builder in Australia, as posted on VansAirforce:
> I've had a constant `bzzt....bzzt...bzzt' sound in my headset repeated at exactly one second intervals. Both pilot and co-pilot sides were affected. The sound level stayed constant despite adjusting the intercom squelch and volume knobs, and was unaffected by the transponder, radio, autopilot or lights. At first I thought the sounds were related to the flashing warning signs on the Dynon, but later realised they were exactly timed to the digital clock on the display. The noise would start as soon as the boot sequence got to `starting network manager'. If I unplugged the GPS antenna from the AV5000 module so that the system couldn't pick up the time signal from the satellites, the clock would not appear and neither would the noise. Dynon initially thought it might be related to the transponder, but neither disconnecting the transponder, the EMS, or anything else seemed to make any difference. If the clock was active, so was the noise. The only way to get rid of it was to di!
sconnect the GPS antenna, which wasn't really a good solution. However, flying with the noise wasn't an option either as it was as irritating as a dripping tap.
> However, I got lucky this afternoon when a local electronics guru happened to be at the field. He spent a couple of hours trouble-shooting the system, checking the Skyview settings, the radio, tracing the wiring diagram, pulling pins, etc, until he eventually discovered that the noise was apparently being generated by interference between the music jack wires and the tunnel harness, which runs to the ADAHRS mounted in the tail cone. When the GPS antenna was connected, it appears that EMF generated in the network cable was being fed into the audio wires that run close to the cable in the tunnel, and was therefore audible in the headsets. Disconnecting the two audio wires fixed the problem. It was a simple solution, but tracking down the cause has been a very frustrating exercise. Glad it's been fixed now.
The length of the shared wire harness is five feet. We will never know the true cause. But is it more likely that the audio interference was due to the proximity of wires, or due to the fact that the stereo music input jack was grounded locally to the airframe (without isolating washers) instead of having a dedicated ground wire running back to the instrument panel ground?
Joe
--------
Joe Gores
For noise problems, I always look at ground issues first. In my opinion,
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he needs to fix the ground issue whether that particular problem was
caused by it or not. And if that jack was grounded, then there may be
others that have similar issues.....
Charlie
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jun 28, 2015 4:45 pm Post subject: Audio Noise |
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| Quote: | For noise problems, I always look at ground issues first. In my opinion, he needs to fix the ground issue whether that particular problem was caused by it or not. And if that jack was grounded, then there may be others that have similar issues.....
Charlie |
Yes . . . this is excellent advice on airframes
where no particular philosophy for grounding
has been adopted BEFORE wires were strung.
Over the years, places like Beech, Cessna, et. als.
developed design and process specs for the construction
of new systems in their products. Noise issues were
rare because lessons learned (some of them painful and
expensive) were core knowledge for development
of those specs.
To be sure, the first question to be explored on
discovery of any noise problem in an OBAM aircraft
is, "What does your ground system architecture look
like?"
Bob . . . [quote][b]
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matronics.list(at)gmail.c
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| Posted: Mon Jun 29, 2015 8:48 am Post subject: Audio Noise |
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I had the exact problem. The sound was caused by an unshelled RS-232 output of my GPS that was putting out NMEA sentences every one second. It was being picked up by a nearby unconnected music input to my audio panel. Grounded the audio input and all was fine.
John Snapp
+1.303.810.0600
(sent from iPhone)
| Quote: | On Jun 28, 2015, at 11:24 AM, user9253 <fransew(at)gmail.com> wrote:
Below is a quote from a RV-12 builder in Australia, as posted on VansAirforce:
> I've had a constant `bzzt....bzzt...bzzt' sound in my headset repeated at exactly one second intervals. Both pilot and co-pilot sides were affected. The sound level stayed constant despite adjusting the intercom squelch and volume knobs, and was unaffected by the transponder, radio, autopilot or lights. At first I thought the sounds were related to the flashing warning signs on the Dynon, but later realised they were exactly timed to the digital clock on the display. The noise would start as soon as the boot sequence got to `starting network manager'. If I unplugged the GPS antenna from the AV5000 module so that the system couldn't pick up the time signal from the satellites, the clock would not appear and neither would the noise. Dynon initially thought it might be related to the transponder, but neither disconnecting the transponder, the EMS, or anything else seemed to make any difference. If the clock was active, so was the noise. The only way to get rid of it was to di!
sconnect the GPS antenna, which wasn't really a good solution. However, flying with the noise wasn't an option either as it was as irritating as a dripping tap.
> However, I got lucky this afternoon when a local electronics guru happened to be at the field. He spent a couple of hours trouble-shooting the system, checking the Skyview settings, the radio, tracing the wiring diagram, pulling pins, etc, until he eventually discovered that the noise was apparently being generated by interference between the music jack wires and the tunnel harness, which runs to the ADAHRS mounted in the tail cone. When the GPS antenna was connected, it appears that EMF generated in the network cable was being fed into the audio wires that run close to the cable in the tunnel, and was therefore audible in the headsets. Disconnecting the two audio wires fixed the problem. It was a simple solution, but tracking down the cause has been a very frustrating exercise. Glad it's been fixed now.
The length of the shared wire harness is five feet. We will never know the true cause. But is it more likely that the audio interference was due to the proximity of wires, or due to the fact that the stereo music input jack was grounded locally to the airframe (without isolating washers) instead of having a dedicated ground wire running back to the instrument panel ground?
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=444125#444125
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