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nuckolls.bob(at)aeroelect
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 Posted: Wed Oct 24, 2012 5:10 am Post subject: turn coordinator causing noise in headset |
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Unless the noise is actually breaking squelch in the radio I'm going
to 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.
Waaayyyy back when, there was a t/c noise incident that
proved to be MAGNETIC radiation directly from the innards
of the instrument. I don't recall now what brand. THAT
fix called for wrapping the plastic instrument case with
ferrous sheet metal. I think he cut it from a gallon can
and put two or three layers around it secured with tie
wraps.
Never had these problems when suck-n-blow systems were
king . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Fri Oct 26, 2012 8:00 am Post subject: turn coordinator causing noise in headset |
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At 10:07 AM 10/26/2012, you wrote:
| Quote: |
jerrytex wrote:
>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.
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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It's an intriguing symptom. The hypothesis has
some weight. Waaayyyy back when, we believed that
a battery offered an effective electromotive mass
across the bus. That bubble burst when I was
fine tuning the feedback loops on the B&C linear
regulators. With a bus voltage above battery-delivery
potential; greater than 12.5 volts and less than
battery-charging potential; less than 14.0 volts,
the battery is essentially 'open circuit'.
The most challenging condition for bench marking
regulator performance was with a fully charged battery
and relatively light loads. Turning a even a 55w
landing light on would appear as a parallel
impedance on the order of 3 ohms . . . perhaps
significant in comparison with the sum of impedances
in this system.
It would be interesting to probe the system with
some test equipment . . .
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.
Bob . . .
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Sun Oct 28, 2012 5:23 am Post subject: Re: turn coordinator causing noise in headset |
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Might I suggest that the T/C noise might be an indication that the T/C needs repair/mods/replacement?
(I have no notion of what is inside it. But I'd sure start looking there.)
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckolls.bob(at)aeroelect
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| Posted: Tue Oct 30, 2012 6:07 am Post subject: turn coordinator causing noise in headset |
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At 02:31 PM 10/29/2012, you wrote:
| Quote: |
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.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=386225#386225
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Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Tue Oct 30, 2012 6:21 am Post subject: turn coordinator causing noise in headset |
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At 02:31 PM 10/29/2012, you wrote:
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.
An interesting narrative! My writings and the
seminars try to emphasize that a part NOT installed
on the airplane is incapable of being a performance/
maintenance issue later. Keeping the parts count down
not only reduces the cost of acquisition and installation,
it reduces the future costs of ownership too.
Pre-assembled products like the hot-box, exp-bus,
and even Greg Richter's "solid-state breaker
board" may blow warm fuzzy siren songs in the
builder's ear . . . while in fact the builder
is trading in his own understanding and system
reliability for the convenience of somebody else's
plug-n-play understanding.
After more than 30 years observation and participation
in this industry, I have yet to see an off-the-shelf
assembly of electro-whizzies that competes in $value$
for a handful of breakers/fuses, switches and a couple
of contactors. Sometimes the best way to drive a nail
is with a hammer.
Bob . . .
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