Today's Message Index:
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1. 11:30 AM - LED landing light filter experiment (Robert L. Nuckolls, III)
2. 11:56 AM - Re: LED landing light filter experiment (James Kilford)
3. 12:25 PM - Re: LED landing light filter experiment (Sacha)
4. 03:09 PM - Re: LED landing light filter experiment (Robert L. Nuckolls, III)
5. 03:09 PM - Re: LED landing light filter experiment (Robert L. Nuckolls, III)
Message 1
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Subject: | LED landing light filter experiment |
A reader sent me a pair of high intensity LED fixtures after he
discovered that they generated an unacceptable radio noise level.
http://tinyurl.com/aytljbg
I jury-rigged a filter from components I use on the BuckPuk supplies
and mounted it to the back of the fixture on short leads.
Emacs!
The reduction of noise at 130 MHz is pronounced. I estimate
30 dB or better. Unfortunately, I've misplaced my set of
precision attenuators so I'm unable to make a quantitative
A vs. B comparison for effectiveness of the filter.
Fortunately, they're cheap. I've ordered some that should be
in early next week. I can put some real numbers on the
experiment then.
The goal is to head off the noise effects at the source. Wiring
to the airplane will be ordinary, off-the-spool unshielded wire.
When I'm ready to send these back to try on his airplane, I'll
try them out on my '87 GMC truck to see how they compare with the stock
headlights.
Watch this space.
Bob . . .
Message 2
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Subject: | Re: LED landing light filter experiment |
Nice work Bob. Do you mind me asking... what is about these LED lights
that makes them so noisy? In my head, LEDs are completely inert and
therefore wouldn't create any interference.
On 23 January 2013 19:28, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> A reader sent me a pair of high intensity LED fixtures after he
> discovered that they generated an unacceptable radio noise level.
>
> http://tinyurl.com/aytljbg
>
> I jury-rigged a filter from components I use on the BuckPuk supplies
> and mounted it to the back of the fixture on short leads.
>
> [image: Emacs!]
>
>
> The reduction of noise at 130 MHz is pronounced. I estimate
> 30 dB or better. Unfortunately, I've misplaced my set of
> precision attenuators so I'm unable to make a quantitative
> A vs. B comparison for effectiveness of the filter.
>
> Fortunately, they're cheap. I've ordered some that should be
> in early next week. I can put some real numbers on the
> experiment then.
>
> The goal is to head off the noise effects at the source. Wiring
> to the airplane will be ordinary, off-the-spool unshielded wire.
> When I'm ready to send these back to try on his airplane, I'll
> try them out on my '87 GMC truck to see how they compare with the stock
> headlights.
>
> Watch this space.
>
> **
>
> ** Bob . . .
>
Message 3
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Subject: | Re: LED landing light filter experiment |
Hi Bob,
If you get satisfactory results from this, I for one would be very intereste
d.
Sacha
On 23/gen/2013, at 19:28, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectr
ic.com> wrote:
> A reader sent me a pair of high intensity LED fixtures after he
> discovered that they generated an unacceptable radio noise level.
>
> http://tinyurl.com/aytljbg
>
> I jury-rigged a filter from components I use on the BuckPuk supplies
> and mounted it to the back of the fixture on short leads.
>
> <9bf4435.jpg>
>
>
> The reduction of noise at 130 MHz is pronounced. I estimate
> 30 dB or better. Unfortunately, I've misplaced my set of
> precision attenuators so I'm unable to make a quantitative
> A vs. B comparison for effectiveness of the filter.
>
> Fortunately, they're cheap. I've ordered some that should be
> in early next week. I can put some real numbers on the
> experiment then.
>
> The goal is to head off the noise effects at the source. Wiring
> to the airplane will be ordinary, off-the-spool unshielded wire.
> When I'm ready to send these back to try on his airplane, I'll
> try them out on my '87 GMC truck to see how they compare with the stock
> headlights.
>
> Watch this space.
>
> Bob . . .
Message 4
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Subject: | Re: LED landing light filter experiment |
At 02:24 PM 1/23/2013, you wrote:
>Hi Bob,
>If you get satisfactory results from this, I for one would be very
>interested.
>Sacha
>
Whether or not this particular configuration is
the dragon slayer remains to be seen . . . but
the dragon will be slain.
Bob . . .
Message 5
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Subject: | Re: LED landing light filter experiment |
At 01:54 PM 1/23/2013, you wrote:
>Nice work Bob. =C2 Do you mind me asking... what
>is about these LED lights that makes them so
>noisy? =C2 In my head, LEDs are completely inert
>and therefore wouldn't create any interference.
You are, of course, correct. The LEDs are very quiet.
Not zero noise . . . the electrical activity in the
light emitting junction is pretty frenetic. But
the aperture (antenna area) is very tiny so it's
hard to detect . . . much less a risk for a noise
source.
The problem is that LEDs are CURRENT operated
devices. You're probably familiar with the ubiquitous
resistor wired in series with an LED to SET the
current flowing through the device. To light an
red LED (typical voltage drop on the order of
2 volts) from a 14v bus, you have to pick a resistor
that causes the desired LED current to flow (30 mA)
with a DROP of 12 volts. This means that the series
resistor dissipates 6 TIMES as much energy as the
LED . . . but it's so small as to be insignificant.
POWER LEDs will demand much larger current values.
Consider this device
http://tinyurl.com/a2sggv4
which is rated at 10 watts. Note that it's rated
to operate at 3 amps so one would guess that
the operating voltage is about 3.3 volts (typical
for white). So, using a simple series resistor
for 14 volt systems would dissipate 30 watts . . .
NOT insignificant.
The elegant solution demands a special kind of
DC to DC converter. VARIABLE voltage input
(say 10 to 16 volts) and CONSTANT current
output (3 A). Now, we can hook perhaps 3 to
6 lamps in series (10 to 20 volt operation)
but at a constant current.
This bit of electronic magic is ALWAYS
noisy. Your computer, tv, and countless
other appliances have similar power supplies
but they're generally qualified to FCC part
15 rules for expected but limited emissions.
No so with LED lamp fixtures from Fuzzy Joe's
Motorcycle shop . . . or 24xydiy.com either.
We had some discussions here on the list about
LED position lights wherein a number of
builders using a particular DIY kit were
experiencing radio noise from the LuxDrive
power supplies recommended for the installation.
This prompted development of the filtered version
of the LuxDrive part which I've offered now
for several years
[]
This board is the foundation for the experimental filter
I crafted for the aforementioned experiment. This jeeped
experiment may not be the ideal way to go for an on-purpose
filter but then, the then, the boards are already fabricated
and in stock.
Our very own Eric Jones offers an LED based tail light
http://tinyurl.com/b377jtv
Which has enjoyed the benefits of creative tailoring to
the task and generates no objectionable noises.
Bob . . .
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