Today's Message Index:
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1. 06:10 AM - Re: Electrical Noise Prevention (messydeer)
2. 08:52 AM - Re: Electrical Noise Prevention (Robert L. Nuckolls, III)
3. 11:42 AM - Re: Electrical Noise Prevention (messydeer)
4. 11:45 AM - To balun or not to balun, that IS the question (Robert L. Nuckolls, III)
5. 06:29 PM - Re: Electrical Noise Prevention (Tim Andres)
6. 09:42 PM - Avionics Dimmer (Tim Andres)
Message 1
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Subject: | Re: Electrical Noise Prevention |
Thanks, Bob :-)
--------
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=305278#305278
Message 2
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Subject: | Re: Electrical Noise Prevention |
At 11:20 PM 7/16/2010, you wrote:
>
<snip>
>How does this look to you? Thanks again for taking your time helping me :-)
>
>
>http://forums.matronics.com//files/cabin_wiring_labeled_836.jpg
In this picture you show a "main bus" . . . what is this?
Normally, the main bus is a contiguous connection by means
of unbroken bar or strip to the power feed side of an array
of breakers or fuses. I.e., this component is already in existence
inside a fuse block . . . or is fabricated and configured
like the bus bars in this photo:
http://aeroelectric.com/Pictures/Breakers/Breaker_Panel_Busing_1.jpg
You also show a panel ground that appears to be on
the side of the fuselage. Is this a floating tie point
for the collection of all ground wires off the panel mounted
accessories? In the various z-figures, I suggest a gathering
of the grounds on what's called a "panel" or "avionics ground
bus". This is intended to offer a single point ground for a fist full
of wires and centrally located to the serviced accessories
(on the panel itself). Further, it is NOT grounded to the
panel structure . . . but serves as a handy way to extend
lots of grounds to the fire wall ground in fewer wires. For
a panel ground, you'd need something like:
http://aeroelectric.com/Pictures/Grounding/Avionics_Bus_3.jpg
and wired like:
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8Q.pdf
where I show 5 strands of 20AWG running from the panel ground
to the fire wall ground. This provides redundant, low resistance
connection (roughly 2 mOhms/Ft equal to 13AWG) between the
two busses. The 5 strands and panel ground provides a much
handier way to deal with grounds on the panel mounted
accessories.
Bob . . .
Message 3
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Subject: | Re: Electrical Noise Prevention |
> In this picture you show a "main bus" . . . what is this?
This is a fuse block fed by a 10awg line from the battery contactor. I had incorrectly
called it a 'bus'. Now I know better.
> You also show a panel ground that appears to be on
> the side of the fuselage. Is this a floating tie point
> for the collection of all ground wires off the panel mounted
> accessories?
The panel ground is made of a section of 'forest of tabs'. I took one 48 tab forest
and cut it into 3 pieces. One is on the hot side of the firewall and is connected
to another section on the cool side via a 5/16" SS bolt. I forget the
exact numbers, but when I measured the resistance of the SS, it was only slightly
higher than brass. I chose SS because of its higher melting point.
A 10awg ground goes from the inside firewall ground to another section of tab forest
for the panel ground. The panel ground is on the outside (lower side) of
the cover to the main fuse block a few inches from the side of the fuselage.
The cover will be piano hinged to the underside of the glareshield. In the pics,
the glareshield is removed, so I've used a bent piece of metal to put the blocks
in about the same position.
Next step is to wrap all the wires together in a spiral wrap starting from where
teh bundle enters the tray on the right side of the fuselage. Feeders and grounds
will branch off where shown.
--------
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=305327#305327
Attachments:
http://forums.matronics.com//files/ground_blocks_951.jpg
Message 4
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Subject: | To balun or not to balun, that IS the question |
>
>Comments/Questions: I'm installing new VOR antenna and cable and
>have a balun question. I see and have studied the balun on your
>page,
>http://www.matronics.com/aeroelectric/articles/BALUN/Balun_Fabrication.html.
>
>However the connection arrangement for the old cable arrangement is
>the same as in in AC 43.13-2B, Pg 29
>http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2043.13-2B.pdf
>. It shows the center conductor NOT attached to an antenna pole.
>
>I plan to use a Garmin SL30 radio. Which balun connection is
>best? (and hopefully why?!) I haven't been able to find anything
>to support either arrangement, so maybe they're functionally equivalent???
There are a variety of ways to fabricate a balun
and some are preferred depending on the impedance
matching task (1:1 vs 4:1). The balun shown in 43-13
is one way to do it but I selected the device I published
because it was easier to build.
One has to be cautious of 43-13 data. For example,
on pages 28 and 29 they make references to "airframe
ground" . . . on p28, they suggest 4 connections to
the airframe.
From a radio frequency performance these grounds are
not necessary/helpful. On a type certificated airplane
one is not allowed to placard the airplane thusly:
WARNING: THIS AIRCRAFT IS NOT QUALIFIED TO
WITHSTAND DIRECT LIGHTNING STRIKES OF ANY
MAGNITUDE. FLIGHT INTO OR IN VICINITY OF
CONVECTIVE WEATHER OFFERS SUBSTANTIAL RISK
OF HAZARD FROM LIGHTNING AND OTHER UGLY
FORCES. ONE IS STRONGLY ADVISED TO REDUCE
RISK BY MAINTAINING COMFORTABLE SPACING FROM
SUCH CONDITIONS.
So, the dedicated acolyte to all things FAR will
feel compelled to add "airframe grounds" to things
that stick out in the breeze on plastic airplanes.
This is irrespective of the fact that at least
couple dozen paragraphs describing "Lightning Quality
Grounds" is necessary to assist the reader in crafting
effective connections for such purposes.
In any case, either balun is a 1:1 line impedance
transformer so it's your choice. Don't worry about
the "airframe ground" . . . unless you enjoy
the excitement of Mother Nature's roller coaster
rides.
Bob . . .
Message 5
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Subject: | Electrical Noise Prevention |
Hi Bob and thanks for the help.
I am trying to understand your comment re: grounds below. Why is the 5X20
AWG better than a single large wire? And why separate panel and avionics
grounds? In my case I had planned either a DB 25 or forest of tabs approach
on the front of the (glass) panel with all local ground needs tied in there,
then a suitable ground run back to the battery. With a rear mounted battery
do you then recommend the 5X20AWG run all the way to the back?
For reference I am building an all electric COZY.
Thanks, Tim Andres
I suggest a gathering
of the grounds on what's called a "panel" or "avionics ground
bus". This is intended to offer a single point ground for a fist full
of wires and centrally located to the serviced accessories
(on the panel itself). Further, it is NOT grounded to the
panel structure . . . but serves as a handy way to extend
lots of grounds to the fire wall ground in fewer wires. For
a panel ground, you'd need something like:
http://aeroelectric.com/Pictures/Grounding/Avionics_Bus_3.jpg
and wired like:
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8Q.pdf
where I show 5 strands of 20AWG running from the panel ground
to the fire wall ground. This provides redundant, low resistance
connection (roughly 2 mOhms/Ft equal to 13AWG) between the
two busses. The 5 strands and panel ground provides a much
handier way to deal with grounds on the panel mounted
accessories.
Bob . . .
Message 6
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I have discovered the PWM Dimmer I have will not work on at least some of my
Garmin equipment. Instead I think I will just use the built in sensing
circuits that is available for this purpose. The equipment in question is
the GNS 430W, GTX 327, PSA 5000EX and Icom A210. Along with GRT HS displays.
I have read elsewhere that the Garmin stuff is fine using the auto dimming,
Anyone have experience with this for or against this decision?
Thanks, Tim Andres
<mailto:rnbraud@yahoo.com>
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