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Thread: Fillet Question

  1. #21

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    So was ACTUAL acoustic feedback! Don't know if I would have thought of it. But makes sense since ANL headsets have microphones pointed outward, toward the pilot's mic.

    Meant to compliment you on your FUN gauge--- I see it's permanently pegged to redline, just the way it should be.

  2. #22
    rwanttaja's Avatar
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    Quote Originally Posted by flyrgreen View Post
    So was ACTUAL acoustic feedback! Don't know if I would have thought of it. But makes sense since ANL headsets have microphones pointed outward, toward the pilot's mic.
    Actually, the situation was way weird. I have an Icom at home (ICA23) that I used as a test unit with the standard Icom headset adaptor and the rubber duckie antenna, and an ICA5 in the airplane with a homemade adaptor (leading to the jacks in the picture) and a coax going to the antenna.

    I wear eight-ohm ear buds and homemade mike holder in warm weather, and a Rugged Radios headset that converted to 8 ohm in cooler weather. Neither has shown any feedback.

    I have a Denali ANL and a cheap non-ANL headset. No squeal for either when plugged into either the airplane-mounted handheld or the separate one on the bench.

    Yet when I did an adaptor, I'd get squeal with either headset in the airplane, but never on the bench unit.

    My working theory was that I was getting some sort of coupling back into the transformer itself. So I did several adaptor units, wrapping them in copper tape, or using long cables so the transformer was nowhere near the radio or the antenna. None of them got rid of the feedback.

    What was most frustrating is that the feedback NEVER occurred with the bench radio. Never. If it did, I would have been able to test various combinations to see that it might be....but it never showed the problem on the bench.

    Until I got desperate.

    I wondered about the sidetone level, so I cranked up my benchtop radio and gradually turned up the sidetone. It did, eventually, start squealing.

    So I went back to the airport and repeated the process, turning DOWN the sidetone level. Sure enough, the noise finally went away, and I could still hear my voice when I transmitted.

    My current thinking is that this was not air-coupled feedback, but the vibration of the headset structure itself being picked up by the microphone. Both my ANL and the cheapie headset use solid mike booms.

    Adding the adaptor increases the headset volume by 6 dB (actual measurement), which is FOUR TIMES the sound energy. That might explain why it was coupling back.

    But...why did the feedback NOT happen with my 8-ohm headsets? The sound level was just as high.

    The Rugged Radios unit has a wire-cage mike holder, vs. the solid, flexible mike holder of the two 300-ohm units. Wonder if that attenuates the vibration better. With the ear-bud headset, there is no physical connection from the speakers to the mike...the ear buds go into my ears, and the microphone is held in place by an entirely different structure.

    In any case, it was causing me lots of grief.

    Quote Originally Posted by flyrgreen View Post
    Meant to compliment you on your FUN gauge--- I see it's permanently pegged to redline, just the way it should be.
    The picture isn't sharp enough to tell, but the needle is ACTUALLY just at the top of the yellow arc. It's a high level of fun, but not necessarily dangerous, yet.


    Construction instructions at:
    http://www.bowersflybaby.com/stories/fun_meter.html

    Ron Wanttaja

  3. #23

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    The solid boom arms holding the mic will definitely transmit much more sound than the wire cage affair.

  4. #24
    rwanttaja's Avatar
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    Well for those who love saying "I told you so..." :-)

    But this didn't break from normal loads. I was getting out to put gas in the airplane and left my headset plugged in. Whacked the adaptor with my knee.

    The external shell is broken as shown, and the glued-on end piece of the internal structure broke free. It can just be glued back into place. I could superglue the external shell, too, but I'll just go for a new one.

    This is the beautiful thing about using Solidworks. If I'd built that from scratch, it'd take me a bit to duplicate, and I'd have to fiddle with the new piece so it'd match the old one. Instead, I just dig up the file and send it to the 3D printer.

    Contemplated adding some thickness or some stiffeners, but I think I'll be satisfied with NOT leaving it plugged in while I climb in or out. If it breaks again, I'll look at some upgrades.

    Ron Wanttaja

  5. #25

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    Sep 2011
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    An ejection seat mishap would have made a much more interesting story, so points to you for keeping it real.

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