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dlj04(at)josephson.com
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 Posted: Tue Oct 23, 2012 10:59 am Post subject: turn coordinator causing noise in headset |
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| Quote: |
It seems like it is coming in through the antenna but why would turning the landing
light on make it go away. Anyone have any ideas? Filter maybe?
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You didn't mention whether the noise is there only when receiving a
signal or in your headset all the time. This is important. If it's only
when you're receiving a signal I would agree with Bob's suggestion that
it's radiated, and a filter would help. Turning the landing light on
probably drops the voltage sufficiently that the current spikes drawn by
the inverter in the t/c are significantly smaller than with the light off.
--
David Josephson
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jerrytex
Joined: 10 Feb 2011
Posts: 12
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| Posted: Tue Oct 23, 2012 12:52 pm Post subject: Re: turn coordinator causing noise in headset |
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The noise is there always, regardless of transmitting or receiving. I can put my headset on, turn on the master, listen to the gyro spin up in the headset, then turn on the landing the light, and the noise goes away. Or I can disconnect the antenna, and the noise goes away. I read on a yahoo group in which someone else was having the same issue but there was no fix listed. I'll try the CAPACITOR and if that doesn't work, I'll order the filter. Thanks for the responses.
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dlj04(at)josephson.com
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| Posted: Tue Oct 23, 2012 11:36 pm Post subject: turn coordinator causing noise in headset |
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| Quote: | From: "jerrytex"<jery230(at)tconline.net>
The noise is there always, regardless of transmitting or receiving. I can put my
headset on, turn on the master, listen to the gyro spin up in the headset, then
turn on the landing the light, and the noise goes away. Or I can disconnect
the antenna, and the noise goes away. I read on a yahoo group in which someone
Unless the noise is actually breaking squelch in the radio I'm going to
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bet on common impedance coupling aka a ground loop, and that your rubber
duck antenna cable is still making a connection to the airframe
somewhere. Is the headset connected directly to the radio, or to an
intercom? Anyway, try the capacitor and then a better filter. Keep the
leads (of either) very short, connect right at the connector of the t/c.
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aero(at)rwaltman.com
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| Posted: Fri Oct 26, 2012 7:09 am Post subject: turn coordinator causing noise in headset |
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jerrytex wrote:
| Quote: | The noise is there always, regardless of transmitting or receiving. I can put my headset on, turn on the master, listen to the gyro spin up in the headset, then turn on the landing the light, and the noise goes away.
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An uneducated guess: The noise is introduced via the supply bus, and
turning the light on somehow provides a lower impedance path to ground
that attenuates it. The suggestion to add capacitors sounds good, how
many and where, that's a different story.
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dlj04(at)josephson.com
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| Posted: Sat Oct 27, 2012 1:24 pm Post subject: turn coordinator causing noise in headset |
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| Quote: | If this antagonist is propagating through the power leads, then an L/C
filter having inductance facing the T/C is called for. The interesting
detail is a notion that the noise spectrum covers VHF frequencies and
gets into the victim via the antenna. This suggests that relatively
small values of L/C would be effective.
It's an interesting puzzle, but I think the antenna part is a wrong tree
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up which to bark. He hears it while transmitting too, and it's in his
headset as soon as he turns on the intercom -- not necessarily on top of
a received signal. My hunch it that it's common impedance coupling and
that the antenna cable is getting a path to ground even for his
"isolated" rubber duck antenna. One of these ground paths or power paths
is shared with the current spikes from the t/c.
Batteries are an effective filter impedance but only in the early part
of their lifecycle. As they age, and long before they stop being
effective batteries, the internal impedance rises. The landing light
doesn't do that.
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jerrytex
Joined: 10 Feb 2011
Posts: 12
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| Posted: Mon Oct 29, 2012 11:31 am Post subject: Re: turn coordinator causing noise in headset |
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As I mentioned earlier, I have had my fair share of electrical issues. It appears that this noise is the result of or partially caused by low voltage directly related to another electrical problem.
The original builder wired in a hotbox. In the hotbox instructions it says to run the two AC lines from the alternator to the hotbox. Apparently some of the Hotboxes had the regulator attached to them and jumpers are need to connect to the regulator. In my case, the regulator is on the firewall. The original builder split the the two AC lines with a crimp connector. He had two AC lines going to the hotbox which were not needed and then had two going to the the regulator with the 12 volt DC line output going to the charging circuit. I discovered that these crimp connectors had bad connections causing resistance and ultimately melted the AC wires together essentially shorting out the AC current. That caused the battery to not charge and caused low voltage. I eliminated the split and ran the AC lines directly to the regulator, crimped and soldered all the connections and the alternator is now charging the battery. I charged the battery with a good battery charger and flew yesterday. It appears that the noise is either gone or lessened to the point that I cannot hear over the engine. So I guess that low voltage was the main culprit with the melted wires causing the low voltage situation by not charging the battery. Thanks for all the thoughts and advice on this.
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