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Intercom feedback at low rpm

 
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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Sun Jan 14, 2018 5:22 pm    Post subject: Intercom feedback at low rpm Reply with quote

Recently I have started hearing static feedback from the intercom during taxi and low rpm such as landing. the noise goes away during flight when rpms are up.. Have been flying for over 100 hours with no trouble, until now. Flightcom 2 person intercom, viking honda engine on a Murphy Rebel.

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PostPosted: Sun Jan 14, 2018 6:26 pm    Post subject: Intercom feedback at low rpm Reply with quote

How is your battery - holding a charge and in good condition otherwise?
On Jan 14, 2018, at 8:22 PM, Rebel56 <Rebel56(at)rogers.com> wrote:



Recently I have started hearing static feedback from the intercom during taxi and low rpm such as landing. the noise goes away during flight when rpms are up.. Have been flying for over 100 hours with no trouble, until now. Flightcom 2 person intercom, viking honda engine on a Murphy Rebel.


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Kellym



Joined: 10 Jan 2006
Posts: 1541
Location: Sun Lakes AZ

PostPosted: Sun Jan 14, 2018 6:28 pm    Post subject: Intercom feedback at low rpm Reply with quote

Do you have a cigar lighter to USB adapter anywhere in the cockpit? For
an Ipad or Iphone, etc?

On 1/14/2018 6:22 PM, Rebel56 wrote:
Quote:


Recently I have started hearing static feedback from the intercom during taxi and low rpm such as landing. the noise goes away during flight when rpms are up.. Have been flying for over 100 hours with no trouble, until now. Flightcom 2 person intercom, viking honda engine on a Murphy Rebel.




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http://forums.matronics.com/viewtopic.php?p=477288#477288











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PostPosted: Sun Jan 14, 2018 6:32 pm    Post subject: Intercom feedback at low rpm Reply with quote

On 1/14/2018 7:22 PM, Rebel56 wrote:
Quote:


Recently I have started hearing static feedback from the intercom during taxi and low rpm such as landing. the noise goes away during flight when rpms are up.. Have been flying for over 100 hours with no trouble, until now. Flightcom 2 person intercom, viking honda engine on a Murphy Rebel.
Need to be more specific describing the symptoms. Feedback (usually a

squeal or howl) is very different from static, and static can be a lot
of different sounds. Is it more of a whine, that changes pitch with rpm?
(likely failing diodes in the alternator) Is it a crackling buzz? Does
it really go away, or can you just not hear it over the increased noise
in the cockpit at higher power settings?

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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Sun Jan 14, 2018 6:34 pm    Post subject: Re: Intercom feedback at low rpm Reply with quote

Battery is in good condition and holds charge.

I have two cigarette lighter adapters, one on each side of the panel.


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Kellym



Joined: 10 Jan 2006
Posts: 1541
Location: Sun Lakes AZ

PostPosted: Sun Jan 14, 2018 6:38 pm    Post subject: Intercom feedback at low rpm Reply with quote

Some USB or mini-USB adapters are bad offenders in the static generation
business.

On 1/14/2018 7:34 PM, Rebel56 wrote:
Quote:


Battery is in good condition and holds charge.

I have two cigarette lighter adapters, one on each side of the panel.




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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Sun Jan 14, 2018 6:39 pm    Post subject: Re: Intercom feedback at low rpm Reply with quote

Been a while since I flew, but I think it could be both, a slight whine, and static. I can quiet it with the squelch, but doing so also quiets all radio traffic. It really seems to disappear when the rpms increase.

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Last edited by Rebel56 on Sun Jan 14, 2018 6:40 pm; edited 1 time in total
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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Sun Jan 14, 2018 6:41 pm    Post subject: Re: Intercom feedback at low rpm Reply with quote

Thanks kellym, I had thought of that as well, and tried unplugging the usb adapter - but no change.

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PostPosted: Sun Jan 14, 2018 6:47 pm    Post subject: Intercom feedback at low rpm Reply with quote

On 1/14/2018 8:39 PM, Rebel56 wrote:
Quote:


Been a while since I flew, but I think it could be both, a slight whine, and static. I can quiet it with the squelch, but doing so also quiets all radio traffic.
Who were you answering? (Need to quote the person you're replying to, if

there are multiple possibilities.)

If it was me, does it change frequency with engine rpm?

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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Sun Jan 14, 2018 6:53 pm    Post subject: Re: Intercom feedback at low rpm Reply with quote

[quote="ceengland7(at)gmail.com"]On 1/14/2018 8:39 PM, Rebel56 wrote:
Quote:


Been a while since I flew, but I think it could be both, a slight whine, and static. I can quiet it with the squelch, but doing so also quiets all radio traffic.
Who were you answering? (Need to quote the person you're replying to, if

there are multiple possibilities.)

If it was me, does it change frequency with engine rpm?

---
It might change frequency ever so slightly, bu the static is constant and loud.


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PostPosted: Mon Jan 15, 2018 6:26 am    Post subject: Intercom feedback at low rpm Reply with quote

On Sun, Jan 14, 2018 at 8:53 PM, Rebel56 <Rebel56(at)rogers.com (Rebel56(at)rogers.com)> wrote:
Quote:
--> Avionics-List message posted by: "Rebel56" <Rebel56(at)rogers.com (Rebel56(at)rogers.com)>

[quote="ceengland7(at)gmail.com"]On 1/14/2018 8:39 PM, Rebel56 wrote:

>
>
>  Been a while since I flew, but I think it could be both, a slight whine, and static. I can quiet it with the squelch, but doing so also quiets all radio traffic.
> Who were you answering? (Need to quote the person you're replying to, if
>

there are multiple possibilities.)

If it was me, does it change frequency with engine rpm?

---
It might change frequency ever so slightly, bu the static is constant and loud.
 
If it doesn't change pitch or volume, it would seem to be unrelated to the engine itself. Have you shed all electrical loads, except the intercom itself? Try to eliminate every electrical device, to see if the noise stops after dropping one of them off line. Any device that contains a 'switcher' style power supply can generate a buzzing noise if it isn't properly filtered. USB power supplies, both LED & HID lighting, strobe lights, CD ignition systems, etc etc can all generate a crackling, buzzing kind of static.
And just to cover all bases, look at engine accessories, too. If possible on the Viking, shut down the alternator. (You should have some form of control over the alternator, to protect your avionics from an over-voltage event.) If it has redundant engine controllers, shut off one controller, then the other, like you would do when doing a mag check on a conventional a/c engine, to see if one of the controllers is causing the noise.
Something as simple as wiring architecture can also cause noise 'injection' into the system. If the plane isn't wired with the grounds from potential noise producers returning to a common point near the battery (meaning that they use a/c structure as the ground return), then noise produced by the device can be imposed on the power circuit of other, vulnerable devices, like the radio and intercom.
Hope that gives you some places to look.


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Rebel56



Joined: 10 Dec 2014
Posts: 11

PostPosted: Mon Jan 15, 2018 3:52 pm    Post subject: Re: Intercom feedback at low rpm Reply with quote

[quote="ceengland7(at)gmail.com"]On Sun, Jan 14, 2018 at 8:53 PM, Rebel56 <Rebel56> wrote:
Quote:
--> Avionics-List message posted by: "Rebel56" <Rebel56>

ceengland7(at)gmail.com wrote:
On 1/14/2018 8:39 PM, Rebel56 wrote:

>
>
>  Been a while since I flew, but I think it could be both, a slight whine, and static. I can quiet it with the squelch, but doing so also quiets all radio traffic.
> Who were you answering? (Need to quote the person you're replying to, if
>

there are multiple possibilities.)

If it was me, does it change frequency with engine rpm?

---
It might change frequency ever so slightly, bu the static is constant and loud.
 
If it doesn't change pitch or volume, it would seem to be unrelated to the engine itself. Have you shed all electrical loads, except the intercom itself? Try to eliminate every electrical device, to see if the noise stops after dropping one of them off line. Any device that contains a 'switcher' style power supply can generate a buzzing noise if it isn't properly filtered. USB power supplies, both LED & HID lighting, strobe lights, CD ignition systems, etc etc can all generate a crackling, buzzing kind of static.
And just to cover all bases, look at engine accessories, too. If possible on the Viking, shut down the alternator. (You should have some form of control over the alternator, to protect your avionics from an over-voltage event.) If it has redundant engine controllers, shut off one controller, then the other, like you would do when doing a mag check on a conventional a/c engine, to see if one of the controllers is causing the noise.
Something as simple as wiring architecture can also cause noise 'injection' into the system. If the plane isn't wired with the grounds from potential noise producers returning to a common point near the battery (meaning that they use a/c structure as the ground return), then noise produced by the device can be imposed on the power circuit of other, vulnerable devices, like the radio and intercom.
Hope that gives you some places to look.


Thanks, all good ideas. When it warms up I will have to start investigating again. Interesting that nothing on the AC has changed, but the noise just started. Loose wire maybe.


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PostPosted: Mon Jan 15, 2018 6:50 pm    Post subject: Intercom feedback at low rpm Reply with quote

Folks,Not certain I have seen it mentioned, but are all the earths clean and with minimum resistance.
Last time I had an intractable nuisance like this, it finally turned out to be a badly earthed headset (female) plug.
Cheers,
Bill Hamilton
[quote]
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