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Thread: Radio noise

  1. #81
    Gordon Misch's Avatar
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    Thank you, sir!
    Gordon

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  2. #82
    BC12D-4-85's Avatar
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    Another source of RF noise can simply be loose spark plug wire caps. When using radio tracking equipment around 50 and 150 Mhz the slightest looseness of a cap on a spark plug created pulsed static on the radios that synched with engine rpms. The caps ground the plug wire shields there and contain ignition noise from getting out with any smoke. P-lead filters can help as well if they're a source of interference.

    Gary

  3. #83
    wireweinie's Avatar
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    I disagree with using filters. Magnetos, alternators, etc, in good working condition won't make enough noise to warrant filters. If an item is generating electrical noise, fix it. Filters simply mask a problem.

    Web
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  4. #84
    BC12D-4-85's Avatar
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    Here's some opinions on filters: https://www.aviationpros.com/engines...c-interference

    Edit: I forgot to warn not to click the link for Sacramento Sky Ranch at the bottom of the article it's been buggy for years.

    Gary
    Last edited by BC12D-4-85; 05-24-2019 at 01:34 PM.

  5. #85
    Gordon Misch's Avatar
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    Here's a new issue for my plane. I recently installed a UAvionics wingtip unit, and I'm experiencing intermittent radio noise associated with its strobe. The unit is wired in accordance with the instructions and operates correctly.

    I know that strobes are the culprit because if I turn off all strobes the noise stops. I know that particular strobe is the culprit because if I turn off the ADSB unit by turning off the nav lights (which also turns off that strobe) while leaving the remaining strobes on and operating, the noise stops.

    My radio is a Garmin SL30

    The noise does not occur on all frequencies, and it will come and go on some frequencies. Freqs I have heard it on are 121.1, 124.2 and 126.5 - all Olympia Wa area freqs for Seattle Center and Seattle approach.

    But the noise is intermittent - seems to be location dependent, and also seems to be when the transmitting station is a bit distant, based on voice clarity from that station. The noise has not shown up on 122.8, 122.9, 124.4 (Olympia tower), 121.6 (Olympia ground) or 118.1 (Portland Approach) , for example. The noise goes away when someone is talking on the frequency. It acts like something is "helping" the strobe hiss to break squelch at some times / places and not others.

    I have not called UAvionics yet, but am thinking someone here may have experienced the issue and can offer advice. Hope so!

    Edit: The noise is also new. The ADSB unit has been installed for almost two months, but the problem has cropped up in the last couple of weeks. Could there be some sort of issue with the transmitting stations which have been problematic?

    Further edit: Two days ago I was at an Olympia avionics shop (unrelated reason involving a friend's plane) so asked the techs there. Unfortunately, the problem would not replicate on the ground there. Of course!

    Thanks - -
    Last edited by Gordon Misch; 05-24-2019 at 01:32 PM.
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  6. #86
    wireweinie's Avatar
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    Noise on some freqs but not on others or worse on some, is a fairly common complaint. Electrical signals spill over onto other frequencies when they get powerful enough. And they get worse on 'multiples' of frequencies. So if you multiply or divide up or down far enough you will usually arrive at the most troublesome frequency. Think of the frequency of the noise OR the receiver. Now multiply/divide by any number (2, 4, 6 . . 5, 10, 15, etc).

    If I were troubleshooting this particular installation, I'd start by checking and cleaning the ground for the light and the uAvionics unit. Then I'd check to see if the Com antenna has a good ground plane and is not mounted on paint or powder coat. Then I'd separate the com coax from any power wires as much as possible. Worse case is that you simply have a strobe that makes noise. It's not common but I have seen LED strobes that make a ticking noise when the flash. Replaced the unit and the noise went away.

    Check all the above stuff first. Then, if the noise continues, contact uAvionics for some help or even a replacement unit.

    Web
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  7. #87
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    Quote Originally Posted by wireweinie View Post
    I disagree with using filters. Magnetos, alternators, etc, in good working condition won't make enough noise to warrant filters. If an item is generating electrical noise, fix it. Filters simply mask a problem.

    Web
    I have older Bendix mags with the coaxial style p-lead connectors. The mags had the coaxial p-lead filters when I bought the plane. A couple of years ago I overhauled the mags, and looking at the filters, decided they were too worn out to use (disintegrating shields, unknown age).

    A new PMA filter (MF3A) with the braided shield to fit the connector is virtually impossible to find. A non-PMA filter is available at Aircraft Spruce for $260, and you need two. A filter without the braided shield is $80, but it seems to me that the shield is needed between the capacitor and the mag case.

    Anyway, after removing the filters, there was a slight increase in magneto noise when receiving weak signals.

    Interestingly, the noise dramatically increased twice, when a plug was fouled, and when the internal capacitor was about to fail (an early life failure on a newly rebuilt mag). So, mag noise can be a diagnostic tool.
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  8. #88
    wireweinie's Avatar
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    Quote Originally Posted by sjohnson View Post
    So, mag noise can be a diagnostic tool.
    Brings me back to my point about fixing the source of the noise.

    Web
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  9. #89
    Gordon Misch's Avatar
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    Thank you Web, I will check all of those that you mentioned
    Gordon

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  10. #90
    wireweinie's Avatar
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    Cool. Let us know what you find.

    Web
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  11. #91
    Wag2+2's Avatar
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    If the radio static goes away when the alternator is turned off, would the cause be within the alternator or wiring to and from? The charging system works fine.

  12. #92
    wireweinie's Avatar
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    Most likely the alternator itself. Most regulators are very low noise in operation but when brushes get short or bearings get rough, these will cause sparks between the brushes and the commutator. That causes a bunch of noise.

    Web
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  13. #93
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Wag2+2 View Post
    If the radio static goes away when the alternator is turned off, would the cause be within the alternator or wiring to and from? The charging system works fine.
    I've seen noise/fixed from:
    1. loose screw on output breaker(would sometimes weld, other time be loose and noisy)
    2. bad grond alt to airframe
    3. bad master solenoid, burnt contractor?


    (not sure if this thread had my method on how to quickly FIND the source of noise?)
    finding gremlins...

    the battery is the big noise filter, any bad connections allow noise that normal the battery will soak up and hide, to be heard....so long before adding a noise filter i hunt for bad connections...


    but to find the bad conection/noisy conection... say like yours alternator sounds


    first use a temporary jumper wire from the case of alternator to battery ground post, run-up test it... is sound still there? if it is gone the problem is in the ground circut, so move end of jumper that was at battery ground to next closer conection to alt (which is the other end of the battery strap at this 2nd step).... and repeat this till you find it...


    if the ground directly to battery terminal did NOT make it go away.....


    do a temp jumperwire from alt out terminal to battery positive terminal.......run-up test it... is sound still there? if it is gone it is in the positive side of alt output circuit, so move end of jumper that was at battery positive to next closer conection to alt (which is the other end of the battery strap at this 2nd step).....and repeat this till you find it...


    and if all that did not work, then i would call it noisy alternator it self....


    this has worked for me on diffrent planes to find a bad master solinod, and a coroded conection on a alt out breaker

  14. #94
    Wag2+2's Avatar
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    Thanks Web and Mike. Will work on it and post what I find. When I turn the radio off in flight and then back on it comes back with quite a jolt so thinking it might be the alternator but will check the wiring. Any alternator recommendations for a Lycoming O-360 angle valve A3A?
    Last edited by Wag2+2; 09-07-2019 at 05:30 PM. Reason: Added

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