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Thread: Radio noise

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