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noise problem on radio

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 21, 2014 6:48 am Post subject: noise problem on radio

URL Corrections. Seems my capture of image URLs out on

the web were flaky . . . I've posted the images to my

website and re-linked them in this repeat of my

earlier posting . . .

================================================================




<nuckolls.bob(at)aeroelectric.com>



The noise is intermittent but seems to be strongly correlated to two things

- when the Autopilot (Trio Avionics ProPilot) is switched on I get much more

noise.  This noise is present even when the engine is off.  It's like the

squelch breaking.



    The image (or sound) that pops to mind with the term

    "squelch breaking" is the sort of white noise you

    get from an receiver when no useful signal is present

    but the volume is turned up. The noise is a combination

    of atmospheric and internally generated noises. Is

    this the kind of noise you're hearing?



For some reason I've noticed that it happens more when I

move the stick back and forth... I have no idea why this may be.

- engine RPM - when I increase the throttle the noise becomes more and seems

to increase in pitch and intensity.



    But it's present even when the engine is not running?



I'm suspecting at least one faulty ground connection.



    Not sure there is foundation for this supposition yet . . .



It's possible that it

could also be due to the fact that the magneto wires (well, I'm not sure

they are real magnetos, the engine is a Rotax 912UL) are not shielded as I

didn't know any better when I wired them the first time.



    The 912 has a form of capacitor discharge ignition system.

    See . . .



http://tinyurl.com/ouvxh42



    The capacitors are charged via separate coils on

    the PM alternator stator stack . . . the larger two

    of ten coils visible here.



http://tinyurl.com/ohkdgc6



   The Rotax manual calls for shielded wire on the ignition control

   lines . . . which is fine . . . but it also calls for the shields

   to be grounded at both ends which is not fine . . . at the

   engine end only and use the shield as a ground for the

   ignition switch. See:



http://tinyurl.com/n3oy37f



   However, since you say the noise is present with the

   engine not running . . . then the wiring of the ignition

   switches is not a likely source of your difficulties.

(Most of the wires that come from the panel go through connectors; in this

way, I can remove the panel from the aircraft by detaching three connectors

and the wire harness to the Autopilot.).



My question is: how do I go about isolating what the fault might be?  I'm

dreading having to take apart every single wire in the avionics

interconnections.



   Study the chapter on noise and formulate a plan . . . it's

   like playing Clue (Mr. Mustard with the Pipe in the Library).

   This is an exercise in hypothesis development and elimination

   which starts with identifying the antagonist. The antagonist's

   nose signature is your first clue . . . so we first need to qualify

   the "breaking squelch" term.

   Bob . . .

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uuccio(at)gmail.com
Guest

Posted: Sat Feb 22, 2014 1:47 pm Post subject: noise problem on radio

Thank you Bob, 

I went back and inspired by your comment about Mr. Clue, I carefully

observed the phenomenon without jumping to conclusions.  It turns out the

interference only happens when the (Trio Avionics Pro Pilot) Autopilot is

ON, even if the engine is OFF.    Attached is a link to a video with sound.

There is a lot of background noise (mostly the sound of the GNS430 fan) but

you can still here the interference and see that it completely disappears

when the AP is turned off.

The interference happens in the form of a RX signal on the radio.  In other

words, whatever is happening is causing the COM radio to think it's

receiving a transmission, as is evidenced by the RX signal that's visible on

the GNS430 screen.    

Anyone have any idea why this might be happening?  I guess my next step is

to see if this also happens on, say, a handheld COM.

Sacha



https://dl.dropboxusercontent.com/u/56559644/Autopilot%20COM%20interference%

20email.mp4

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 25, 2014 7:45 am Post subject: noise problem on radio

At 03:46 PM 2/22/2014, you wrote:

 	  Quote: 	
		  



Thank you Bob,

I went back and inspired by your comment about Mr. Clue, I carefully

observed the phenomenon without jumping to conclusions.  It turns out the

interference only happens when the (Trio Avionics Pro Pilot) Autopilot is

ON, even if the engine is OFF.


	


   Good work!



 	  Quote: 	
		      Attached is a link to a video with sound



The interference happens in the form of a RX signal on the radio.  In other

words, whatever is happening is causing the COM radio to think it's

receiving a transmission, as is evidenced by the RX signal that's visible on

the GNS430 screen.


	


   Okay, it's perceived as a radiated signal that

   comes in through the antenna coax. Have you

   checked SWR on the comm antenna? If your shield

   ground is loose at the radio, it can open a

   pathway for conducting otherwise insignificant

   signals into the receiver.



   Is there an installation/wiring manual for the

   AP that can be downloaded from the 'net? Also,

   you could 'sniff' around with a handheld. I'd

   craft a couple of probes to put onto your hand-held's

   antenna jack.



   An e-field probe consisting of a dime-sized

   disk supported on about an inch off the back

   end of the BNC connector. Also an h-field probe

   consisting of two turns of wire about 3/4" diam

   connected across a BNC connection on 1" of twisted

   leads.



   Open the squelch on the hand held and move the

   attached probes over components and wiring of the

   a/p to see if you can identify the strongest

   manifestation of the noise.

   Bob . . .

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uuccio(at)gmail.com
Guest

Posted: Tue Feb 25, 2014 9:23 am Post subject: noise problem on radio

 	  Quote: 	
		      Attached is a link to a video with sound



The interference happens in the form of a RX signal on the radio.  In 

other words, whatever is happening is causing the COM radio to think 

it's receiving a transmission, as is evidenced by the RX signal that's 

visible on the GNS430 screen.


	


   Okay, it's perceived as a radiated signal that

   comes in through the antenna coax. Have you

   checked SWR on the comm antenna?



No, I haven't.  Is it worth getting my hands on an SWR meter?



   If your shield  ground is loose at the radio, it can open a

   pathway for conducting otherwise insignificant

   signals into the receiver.



You mean that the coax shield could not connected or improperly connected to

the appropriate BNC terminal?  I actually have the coax connected to a

backplate connector to which the GNS430 connector slides into, so I guess

there is extra potential there for them not to properly connect (e.g. if the

radio is not properly slotted into the backplate connector).  



   Is there an installation/wiring manual for the

   AP that can be downloaded from the 'net? 



http://www.trioavionics.com/Pro%20Pilot%20Manual%203.8.pdf 



   Also,

   you could 'sniff' around with a handheld. I'd

   craft a couple of probes to put onto your hand-held's

   antenna jack.



I sniffed around yesterday with the handheld and its regular antenna.  What

I noticed was that as soon as I switch on the Avionics and the handheld

antenna is close to them, I hear a bunch of noise, but I guess that's

normal.  When I switch on the AP and move the handheld antenna close to the

servo cables (that are shielded), I can hear a stronger kind of buzzing

noise.  I really have to be almost touching those shielded cables though in

order to pick anything up.     I didn't try putting the antenna close to the

radio's COM coax connector though.



   An e-field probe consisting of a dime-sized

   disk supported on about an inch off the back

   end of the BNC connector. Also an h-field probe

   consisting of two turns of wire about 3/4" diam

   connected across a BNC connection on 1" of twisted

   leads.



Do you have any pictures of how to build these?   Is this

http://www.emcesd.com/tt120100.htm the right idea?



   Open the squelch on the hand held and move the

   attached probes over components and wiring of the

   a/p to see if you can identify the strongest

   manifestation of the noise.	



   Bob



Thanks again for the suggestions!

Regards

Sacha

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 27, 2014 6:16 am Post subject: noise problem on radio

No, I haven't.  Is it worth getting my hands on an SWR meter?



    If your shield  ground is loose at the radio, it can open a

    pathway for conducting otherwise insignificant

    signals into the receiver.



    If you don't have ready access to one, hold off acquiring

    it. But check the mechanical integrity of your coax

    connections at the back of the radio. How well does the

    comm transceiver work? Have you detected any shortfall

    in performance?

http://www.trioavionics.com/Pro%20Pilot%20Manual%203.8.pdf



    Okay . . . that's a busy little box. Refresh my

    memory, is this noise a new thing or has it always

    been present. Also, when receiving a weak signal

    (tune in an ATIS and fly away from airport until

    signal starts to get noisy . . . then turn a/p

    on/off and judge how much effect the a/p noise

    has on reception of weak signals).



I sniffed around yesterday with the handheld and its regular antenna.  What

I noticed was that as soon as I switch on the Avionics and the handheld

antenna is close to them, I hear a bunch of noise, but I guess that's

normal.  When I switch on the AP and move the handheld antenna close to the

servo cables (that are shielded), I can hear a stronger kind of buzzing

noise.  I really have to be almost touching those shielded cables though in

order to pick anything up.     I didn't try putting the antenna close to the

radio's COM coax connector though.



    You wont see any noise coming OUT of this junction,

    but it is a potential point of ingress for noises

    that tend to pile up behind the panel.



Do you have any pictures of how to build these?   Is this

http://www.emcesd.com/tt120100.htm the right idea?



    Yes! good find. I got a little ahead of myself

    in sifting the simple ideas. Don't run off and build

    one (or e-field probe) yet.



    It's not clear to me yet as to operational significance

    of the noise. DO-160 ALLOWS certain levels of noise

    while putting potential victims ON NOTICE that such

    noises may be present but normally insignificant.



    My sense of the situation from your narrative

    so far is that while the A/P is a noteworthy

    contributor . . . it's not the sole potential

    antagonist . . . we may discover that it is

    within practical limits and you just need to

    tighten the squelch on the receiver a tad.



    I think I've related my experiences with the

    symphony of noises that are often heard in

    various systems while sitting on the ground

    with engines off and wearing headphones . . .

    noises that are completely insignificant

    while in flight.



    Let's size the task before we get out hammers-

    n-saws.



    Bob . . .





   Bob . . .

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uuccio(at)gmail.com
Guest

Posted: Sun Mar 02, 2014 2:11 pm Post subject: noise problem on radio

No, I haven't.  Is it worth getting my hands on an SWR meter?



    If your shield  ground is loose at the radio, it can open a

    pathway for conducting otherwise insignificant

    signals into the receiver.



    If you don't have ready access to one, hold off acquiring

    it. But check the mechanical integrity of your coax

    connections at the back of the radio. How well does the

    comm transceiver work? 



I don't have enough experience with it yet.  In Italy, ultralights can only

speak to other such a/c on 130 MHz.  You need to acquire an "advanced"

ultralight license (which costs approx.. $2000) to be able to talk to

anybody else.  It's all part of the ridiculous regulation we endure here.



	Have you detected any shortfall in performance?



(In my limited experience), not so far.  



http://www.trioavionics.com/Pro%20Pilot%20Manual%203.8.pdf



    Okay . . . that's a busy little box. Refresh my

    memory, is this noise a new thing or has it always

    been present. 



I only noticed it in the last 10 hours or so, but the a/c only has 30 hours

or so since I rebuilt it, and I wasn't particularly concentrating on the use

of the radio initially since a) there's hardly any other traffic around and

b) I'm limited to the ultralight air-to-air frequency in any case.



    Also, when receiving a weak signal  (tune in an ATIS and fly away from

airport until

    signal starts to get noisy . . . then turn a/p

    on/off and judge how much effect the a/p noise

    has on reception of weak signals).



I will try that next time.  



    [...] My sense of the situation from your narrative

    so far is that while the A/P is a noteworthy

    contributor . . . it's not the sole potential

    antagonist . . . we may discover that it is

    within practical limits and you just need to

    tighten the squelch on the receiver a tad.



I'll try that next time too.



    I think I've related my experiences with the

    symphony of noises that are often heard in

    various systems while sitting on the ground

    with engines off and wearing headphones . . .

    noises that are completely insignificant

    while in flight.



    Let's size the task before we get out hammers-

    n-saws.

   Bob . . . 



What you say makes sense.  I'm going to be away from the hangar for a few

weeks (I'm actually going to New Mexico for a job interview and then to

Socal to see some friends), so I'll pick the thread up again when I get

back.  



Sacha

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