Today's Message Index:
----------------------
1. 06:21 AM - Re: Headset RFI (Robert L. Nuckolls, III)
2. 06:46 AM - Computer power supplies (Dr. Andrew Elliott)
3. 07:45 AM - DO-160 - - again (George Braly)
4. 08:37 AM - VHF antenna placement wrt transponder antenna (Mickey Coggins)
5. 11:27 AM - Re: Headset RFI (Chuck Jensen)
6. 12:17 PM - DO-160 - - again (Eric M. Jones)
7. 12:18 PM - Ground and braded wire. (Johann G.)
8. 12:33 PM - Skymap GPS display has lines missing (HAL KEMPTHORNE)
9. 12:39 PM - Re: Ground and braded wire. (John)
10. 12:50 PM - Re: Skymap GPS display has lines missing (Smcm75@aol.com)
11. 01:30 PM - Re: Ground and braded wire. (Johann G.)
12. 02:25 PM - Re: Ground and braded wire. (BobsV35B@aol.com)
13. 02:28 PM - Re: Ground and braded wire. (BobsV35B@aol.com)
14. 02:59 PM - Re: Ground and braded wire. (Matt Prather)
15. 05:54 PM - Re: Skymap GPS display has lines missing (Charlie England)
16. 06:37 PM - Re: Ground and braded wire. (Robert McCallum)
17. 11:06 PM - Re: DO-160 - - again (Robert L. Nuckolls, III)
18. 11:18 PM - Re: Ground and braded wire. (Robert L. Nuckolls, III)
19. 11:21 PM - Re: Ground and braded wire. (Robert L. Nuckolls, III)
Message 1
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 04:18 PM 12/11/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: Chuck Jensen <cjensen@dts9000.com>
>
>I recently installed UMA instrument bezel lighting. The UMA system uses an
>inverter to power the bezel lights with up to 115v. I like the soft
>blue/green flow and by dimming, instrument lighting is great under all
>conditions. However, when the bezel lights are turned on, a very noticeable
>whine is present in the background during transmit or intercom
>communications. The avionics shop said "some installations are quiet but
>its pretty common to have the RFI from the UMA bezel lighting system and
>there's no way to fix it without a lot of research (re: dollars). It seems
>hard to believe that a system would be design and sold that 'commonly'
>induces whine into the radio system--and there's no cure. Is this true or
>just a cop-out?
It's a cop-out. If UMA were asked to conduct the very rudimentary
tests per DO-160 that would be expected for qualifying these products
onto certified aircraft, there would be no noticeable noise. It should
NOT be common to have any noise in the system due to the effects of this
product.
The techniques for fixing this are the same as outlined in Chapter
16. You know the victim, you know the antagonist, now deduce the
propagation path and attenuate or break it. Then publish your
findings here on the list and elsewhere.
Bob . . .
Message 2
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| Subject: | Computer power supplies |
--> AeroElectric-List message posted by: "Dr. Andrew Elliott" <a.s.elliott@cox.net>
Anyone using a computer power supply for shop power? You can get these
with one of the 12V output rated at 20 or 25 amps, for <$10 usually. Is
the 12V too low? Most "regular" regulated switching power supplies are
13.8V, like your VR output.
Andy Elliott
Lycoming owner, Corvair wannabe!
Message 3
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| Subject: | DO-160 - - again |
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
Bob, A friend who is involved in a certified project was doing DO-160 testing
for the 80 volt spoke on the power leads.
He was blowing equipment - - when I quizzed him about the duration of the pulse.
He said they were testing at 80volts for 400 ms.
I pulled out the DO-160 and it only specifies the 80 volts for 100ms.
He was surprised - - but it turns out the OEM for which the equipment is being
developed specified the 400ms duration.
Can you think of any reason why they would do that ?
Have you come across this before?
Regards, George
---
Message 4
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| Subject: | VHF antenna placement wrt transponder antenna |
--> AeroElectric-List message posted by: Mickey Coggins <mick-matronics@rv8.ch>
Hi,
I've read in the archives that one should place two
VHF antennas as far apart as possible, and Brian
recommends one on the top, and one on the bottom.
I also read that Garmin recommends 30 inches distance
between a VHF Comm antenna and one of their GPS antennas.
My question is should a VHF Comm antenna be placed a
certain distance from a transponder antenna?
Many thanks,
Mickey
--
Mickey Coggins
http://www.rv8.ch/
#82007 QB Wings/Fuselage
Message 5
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--> AeroElectric-List message posted by: Chuck Jensen <cjensen@dts9000.com>
Actually, UMA has conducted extensive testing and confirms the RFI is
neither normal or acceptable. They were very helpful in making several
suggestions of places to look for the problem and I will read your Chapter
16 as part of my OEP (Ongoing Education Program). I will certainly post the
results for all to assimilate.
Chuck
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Robert
L. Nuckolls, III
Subject: Re: AeroElectric-List: Headset RFI
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
At 04:18 PM 12/11/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: Chuck Jensen <cjensen@dts9000.com>
>
>I recently installed UMA instrument bezel lighting. The UMA system uses an
>inverter to power the bezel lights with up to 115v. I like the soft
>blue/green flow and by dimming, instrument lighting is great under all
>conditions. However, when the bezel lights are turned on, a very
noticeable
>whine is present in the background during transmit or intercom
>communications. The avionics shop said "some installations are quiet but
>its pretty common to have the RFI from the UMA bezel lighting system and
>there's no way to fix it without a lot of research (re: dollars). It seems
>hard to believe that a system would be design and sold that 'commonly'
>induces whine into the radio system--and there's no cure. Is this true or
>just a cop-out?
It's a cop-out. If UMA were asked to conduct the very rudimentary
tests per DO-160 that would be expected for qualifying these products
onto certified aircraft, there would be no noticeable noise. It should
NOT be common to have any noise in the system due to the effects of this
product.
The techniques for fixing this are the same as outlined in Chapter
16. You know the victim, you know the antagonist, now deduce the
propagation path and attenuate or break it. Then publish your
findings here on the list and elsewhere.
Bob . . .
Message 6
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| Subject: | DO-160 - - again |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
>I pulled out the DO-160 and it only specifies the 80 volts for 100ms.
>He was surprised - - but it turns out the OEM for which the equipment is
being
>developed specified the 400ms duration.
>Can you think of any reason why they would do that ?
George,
As Bob Might Say.....
Google "SC135 DO-160E". This is the working group on the NEW-THIS-MONTH
DO-160E. Basically two forces, harmonization and the gradual attempt to
civilize us have conspired to boost immunity levels. I don't have the
patience to download from this website, but if it's anywhere, It's here.
Good luck.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
Message 7
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| Subject: | Ground and braded wire. |
--> AeroElectric-List message posted by: "Johann G." <johann@gi.is>
Hello Bob.
I am very confused but willing to learn.
My problem is not major but misleading when I look at different wire schematics
for my radio and intercom.
The work I am doing is connecting the mic/headphone jack connections to my radio
and intercom.
On your homepage you show how to connect the mike jack and where you refer to the
ground as the shield ground.
My plane will be a two seater, so I will have one cable with three wires and the
shield wire. One for mic high and one with ptt. Then ground with the shield
wire?
When I look at the wire schematic for the PM 1000 intercom, it indicates that I
should "connect the shields at intercom only".
My question is: Should I use the shield wire as the ground on both ends in the
mic and headphone connections?
Sorry for the long and confusing question.
Thank you in advance.
Johann G.
Message 8
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| Subject: | Skymap GPS display has lines missing |
--> AeroElectric-List message posted by: HAL KEMPTHORNE <hal_kempthorne@sbcglobal.net>
Hi,
My Skyforce Skymap II monochrome unit is now missing a line. Line near top does
not light up. Works fine otherwise.
Can this be reasonably fixed or should I find a newer unit - this one is about
8 years old.
hal
Message 9
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DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
s=s1024; d=yahoo.com;
b=CYnkeniLtafPes5RXZ2PNFpZym7zJQzVhVfN5N1uaQBfuMnPZ3OH5NqNQJxSRMikPzoZXrQ5OYPmH7xTuGDKf1bPTj3uY1cb5um7T8LICOZ1+g40+ktlC/5gYB9V64mexdUoAhEykIOe46FnQTMi1dBs+gH9pmcw6O0GaNO5nL8=
;
| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: John <m2mustang@yahoo.com>
No. It's my understanding that the shield will cease
to be a shield if it's connected at both ends.
Only effective when terminated at the end indicated.
JD
--- "Johann G." <johann@gi.is> wrote:
> --> AeroElectric-List message posted by: "Johann G."
> <johann@gi.is>
>
> Hello Bob.
>
> I am very confused but willing to learn.
> My problem is not major but misleading when I look
> at different wire schematics for my radio and
> intercom.
> The work I am doing is connecting the mic/headphone
> jack connections to my radio and intercom.
> On your homepage you show how to connect the mike
> jack and where you refer to the ground as the shield
> ground.
> My plane will be a two seater, so I will have one
> cable with three wires and the shield wire. One for
> mic high and one with ptt. Then ground with the
> shield wire?
> When I look at the wire schematic for the PM 1000
> intercom, it indicates that I should "connect the
> shields at intercom only".
> My question is: Should I use the shield wire as the
> ground on both ends in the mic and headphone
> connections?
>
> Sorry for the long and confusing question.
> Thank you in advance.
> Johann G.
>
>
>
> -
> Contributions
> any other
> Forums.
>
> http://www.matronics.com/subscription
> http://www.matronics.com/FAQ/AeroElectric-List.htm
> http://www.matronics.com/archives
> http://www.matronics.com/photoshare
> http://www.matronics.com/emaillists
>
>
>
>
>
>
__________________________________
http://my.yahoo.com
Message 10
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| Subject: | Re: Skymap GPS display has lines missing |
--> AeroElectric-List message posted by: Smcm75@aol.com
In a message dated 12/14/04 3:33:41 PM Eastern Standard Time,
hal_kempthorne@sbcglobal.net writes:
> Can this be reasonably fixed or should I find a newer unit - this one is
> about 8 years old.
>
>
Message 11
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: "Johann G." <johann@gi.is>
Hello John.
Thanks for the reply,
Yes, this was my understanding too, so this is why I am all confused on the
connecting according to the picture from Bob at aeroelectric.
The picture for the mike jack connection indicates that the
sleeve(common)terminal is the shield ground???? and to get a ground
connection at the other end i.e. radio and intercom, it will also need to be
connected on that end.
This just gets very confusing for someone like me who do not know much about
electrical stuff.
Best regards,
Johann G.
----- Original Message -----
From: "John" <m2mustang@yahoo.com>
Subject: Re: AeroElectric-List: Ground and braded wire.
> --> AeroElectric-List message posted by: John <m2mustang@yahoo.com>
>
> No. It's my understanding that the shield will cease
> to be a shield if it's connected at both ends.
> Only effective when terminated at the end indicated.
> JD
> --- "Johann G." <johann@gi.is> wrote:
>
> > --> AeroElectric-List message posted by: "Johann G."
> > <johann@gi.is>
> >
> > Hello Bob.
> >
> > I am very confused but willing to learn.
> > My problem is not major but misleading when I look
> > at different wire schematics for my radio and
> > intercom.
> > The work I am doing is connecting the mic/headphone
> > jack connections to my radio and intercom.
> > On your homepage you show how to connect the mike
> > jack and where you refer to the ground as the shield
> > ground.
> > My plane will be a two seater, so I will have one
> > cable with three wires and the shield wire. One for
> > mic high and one with ptt. Then ground with the
> > shield wire?
> > When I look at the wire schematic for the PM 1000
> > intercom, it indicates that I should "connect the
> > shields at intercom only".
> > My question is: Should I use the shield wire as the
> > ground on both ends in the mic and headphone
> > connections?
> >
> > Sorry for the long and confusing question.
> > Thank you in advance.
> > Johann G.
> >
> >
> >
> > -
> > Contributions
> > any other
> > Forums.
> >
> > http://www.matronics.com/subscription
> > http://www.matronics.com/FAQ/AeroElectric-List.htm
> > http://www.matronics.com/archives
> > http://www.matronics.com/photoshare
> > http://www.matronics.com/emaillists
> >
> >
> >
> >
> >
> >
>
>
> __________________________________
> http://my.yahoo.com
>
>
Message 12
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: BobsV35B@aol.com
In a message dated 12/14/2004 3:31:55 P.M. Central Standard Time,
johann@gi.is writes:
Thanks for the reply,
Yes, this was my understanding too, so this is why I am all confused on the
connecting according to the picture from Bob at aeroelectric.
The picture for the mike jack connection indicates that the
sleeve(common)terminal is the shield ground???? and to get a ground
connection at the other end i.e. radio and intercom, it will also need to be
connected on that end.
This just gets very confusing for someone like me who do not know much about
electrical stuff.
Best regards,
Johann G.
Good Evening Johan and John,
This is way out of my area of expertise, but as I understand it, what you
want to do is isolate the wiring and the jacks from any airframe ground.
Use the shield as the return to the intercom unit. The jacks themselves
also want to be isolated from the airframe ground. The intent is to shield the
data wires and avoid any potential for a ground loop via an airframe ground.
Dopes that muddy the waters sufficiently?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
Message 13
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: BobsV35B@aol.com
In a message dated 12/14/2004 4:26:21 P.M. Central Standard Time,
BobsV35B@aol.com writes:
Dopes that muddy the waters sufficiently
OOOPS!
Should read: "Does that muddy the water sufficiently?"
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
Message 14
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
You have to consider what is going on in the circuit. Is the outer
conductor (shield) which is wrapped around an (some) inner
conductor(s) providing a signal connection in a circuit? Or is it there
to block the electrostatic propagation of noise?
Moving low frequency electrical energy (audio) from one device to
another (microphone to radio) requires a pair of conducting paths - a
circuit must exist - a signal ("+") and a reference ("-", "ground") conductor
must be used. Two wires can used, as can shielded, single strand
wire. In the case of shielded wire, normally, the center conductor
carries the "+" signal, and the outer shield carries the "-" (ground/
reference) signal. This isn't really a case of shielding so much as
a coaxially oriented signal pair.
To correctly wire a microphone to an intercom using shielded wire,
one terminal on the mic is connected to the center conductor, and the
other terminal is connected to the shield. On the intercom end, connect
the center conductor to the "+" input, and connect the shield to the "-"
terminal. Many devices like this have the "-" terminal connected to
the chassis or power supply ground. Don't think about this too much.
Just remember that a mic needs to be connected to 2 conductors and
the two conductors need to be connected to intercom. Don't consider
making any "extra" connections, by "grounding," etc.
Additionally, I recommend that the PTT circuit does not share any
conductors with the microphone circuit. If you have shielded wire that
has 3 wires plus the shield (4 conductors), using 2 of the wires for PTT,
1 for the mic, and the shield for the mic "-" side should be safe. None
the less, I'd still use seperate wires for this circuit.
One common source of confusion with regard to "grounding" and
"shielding" is magneto wiring... To turn off a magneto (disable its spark),
the p-lead terminal is connected to the body of the magneto (Don't use
the word "ground." Lots of things are electrically connected to the body
of the magneto - it's metal and it's bolted to the engine). To make the
magneto controllable from the cockpit, the p-lead connection to the body
is wired through a switch on the panel. When the magneto is running, the
p-lead is electrically disconnected from the magneto body by opening a
switch in the cockpit. The only down side of this is that the p-lead is
still
connected to the noise generating part of the magneto, and thus can radiate
some noise into other circuits in the airplane. To reduce this effect, the
conductor that goes from the switch in the cockpit to the body of the
magneto can be arranged such that it electrostatically shields the noisy
part of the p-lead. Hence, there is shielded wire between the magneto switch
and magneto. No other connections should be made. Some people say you
"ground" the shield, but really you are just completing the circuit from the
p-lead terminal to the switch in the panel to the body of the mag. Making a
connection between the outer shield and a ground in the cockpit would be
extraneous to the function of the circuit and would be inviting trouble.
In general, if you consider where you have to move electrons, what things
you make wire connections to will become obvious. If you don't have to
allow electrons to get from one thing to another, they don't need (shouldn't
have) wires (conducting paths) connecting them.
Sorry if this was too long to help.. :)
Regards,
Matt-
> --> AeroElectric-List message posted by: "Johann G." <johann@gi.is>
>
> Hello John.
>
> Thanks for the reply,
> Yes, this was my understanding too, so this is why I am all confused on
> the connecting according to the picture from Bob at aeroelectric.
> The picture for the mike jack connection indicates that the
> sleeve(common)terminal is the shield ground???? and to get a ground
> connection at the other end i.e. radio and intercom, it will also need
> to be connected on that end.
> This just gets very confusing for someone like me who do not know much
> about electrical stuff.
> Best regards,
> Johann G.
>
>
> ----- Original Message -----
> From: "John" <m2mustang@yahoo.com>
> To: <aeroelectric-list@matronics.com>
> Subject: Re: AeroElectric-List: Ground and braded wire.
>
>
>> --> AeroElectric-List message posted by: John <m2mustang@yahoo.com>
>>
>> No. It's my understanding that the shield will cease
>> to be a shield if it's connected at both ends.
>> Only effective when terminated at the end indicated.
>> JD
>> --- "Johann G." <johann@gi.is> wrote:
>>
>> > --> AeroElectric-List message posted by: "Johann G."
>> > <johann@gi.is>
>> >
>> > Hello Bob.
>> >
>> > I am very confused but willing to learn.
>> > My problem is not major but misleading when I look
>> > at different wire schematics for my radio and
>> > intercom.
>> > The work I am doing is connecting the mic/headphone
>> > jack connections to my radio and intercom.
>> > On your homepage you show how to connect the mike
>> > jack and where you refer to the ground as the shield
>> > ground.
>> > My plane will be a two seater, so I will have one
>> > cable with three wires and the shield wire. One for
>> > mic high and one with ptt. Then ground with the
>> > shield wire?
>> > When I look at the wire schematic for the PM 1000
>> > intercom, it indicates that I should "connect the
>> > shields at intercom only".
>> > My question is: Should I use the shield wire as the
>> > ground on both ends in the mic and headphone
>> > connections?
>> >
>> > Sorry for the long and confusing question.
>> > Thank you in advance.
>> > Johann G.
>> >
>> >
>> >
>> > -
>> > Contributions
>> > any other
>> > Forums.
>> >
>> > http://www.matronics.com/subscription
>> > http://www.matronics.com/FAQ/AeroElectric-List.htm
>> > http://www.matronics.com/archives
>> > http://www.matronics.com/photoshare
>> > http://www.matronics.com/emaillists
>> >
>> >
>> >
>> >
>> >
>> >
>>
>>
>> __________________________________
>> http://my.yahoo.com
>>
>>
>
>
Message 15
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| Subject: | Re: Skymap GPS display has lines missing |
--> AeroElectric-List message posted by: Charlie England <ceengland@bellsouth.net>
HAL KEMPTHORNE wrote:
>--> AeroElectric-List message posted by: HAL KEMPTHORNE <hal_kempthorne@sbcglobal.net>
>
>
>Hi,
>
>My Skyforce Skymap II monochrome unit is now missing a line. Line near top does
not light up. Works fine otherwise.
>
>Can this be reasonably fixed or should I find a newer unit - this one is about
8 years old.
>
>hal
>
Can't speak directly to the Skymap, but it's almost universal that there
will be a cable & connector between the display & the rest of the
product. It's fairly common for connectors to corrode and/or come loose
& if that's happened, you could get that sort of symptom.
If it's out of warranty & you're confident of your ability to handle
tiny fragile stuff, open it up & reseat the connector.
Charlie
(Just had to do that to wife's in-warranty Dell laptop, at the direction
of tech support.)
Message 16
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: Robert McCallum <robert.mccallum2@sympatico.ca>
Johann
The part that you're missing is in using the term "ground". In your
description stop at the word "shield" and forget the word "ground". It
will make understanding easier. "Shield" and "ground" are NOT synonymous
and are two totally separate things. The braid or shield on the wire is,
in fact, connected to the sleeve of your microphone jack, but because
the jack is electrically isolated from the airframe (or should be) this
does not constitute a "ground", only a return path to the radio/audio
panel etc. to complete the circuit for the microphone. (this wire may
actually be "grounded" at the radio but if you ignore the "ground" bit
and think of it as a return path for the mic signal it becomes easier to
understand)
Hope I haven't added to the confusion;
Bob McC
Johann G. wrote:
>--> AeroElectric-List message posted by: "Johann G." <johann@gi.is>
>
>Hello John.
>
>Thanks for the reply,
>Yes, this was my understanding too, so this is why I am all confused on the
>connecting according to the picture from Bob at aeroelectric.
>The picture for the mike jack connection indicates that the
>sleeve(common)terminal is the shield ground???? and to get a ground
>connection at the other end i.e. radio and intercom, it will also need to be
>connected on that end.
>This just gets very confusing for someone like me who do not know much about
>electrical stuff.
>Best regards,
>Johann G.
>
>
Message 17
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| Subject: | Re: DO-160 - - again |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:18 AM 12/14/2004 -0600, you wrote:
>--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
>
>
>Bob, A friend who is involved in a certified project was doing DO-160
>testing for the 80 volt spoke on the power leads.
>
>He was blowing equipment - - when I quizzed him about the duration of the
>pulse. He said they were testing at 80volts for 400 ms.
>
>I pulled out the DO-160 and it only specifies the 80 volts for 100ms.
>
>He was surprised - - but it turns out the OEM for which the equipment is
>being developed specified the 400ms duration.
>
>Can you think of any reason why they would do that ?
>
>Have you come across this before?
Yeah . . . from time to time, someone decides there's a reason
to exceed requirements of DO-160 for being able to withstand
applied stresses. Does this product go into a certified
airplane? Most of our new black boxes are tested to category
B . . . battery of significant capacity on bus and category
A for airplanes like the Hawker Horizon (AC generators with
TR sets to develop DC). Both of these requirements are much
easier to meet than category Z (assumes generator runaway
happens with no battery on line too). Actually, ov protection
circuits are so much better than 30 years ago when the values
were selected, I'd have no problems with testing all 28VDC
stuff for category B as long as the ov protection system was
modern.
The guy needs to inquire as to the rationale for departing
from the 80v, 100 mS values as described in 16.5.4.4.b
of DO-160.
While DO-160 defines ability to withstand, MIL-STD-704
describes the ability to limit aberrations on the bus.
and 80v, 400 mS transient is certainly well outside the
design goals suggested by MIL-STD-704.
Bob . . .
Message 18
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 08:17 PM 12/14/2004 +0000, you wrote:
>--> AeroElectric-List message posted by: "Johann G." <johann@gi.is>
>
>Hello Bob.
>
>I am very confused but willing to learn.
>My problem is not major but misleading when I look at different wire
>schematics for my radio and intercom.
>The work I am doing is connecting the mic/headphone jack connections to my
>radio and intercom.
>On your homepage you show how to connect the mike jack and where you refer
>to the ground as the shield ground.
>My plane will be a two seater, so I will have one cable with three wires
>and the shield wire. One for mic high and one with ptt. Then ground with
>the shield wire?
>When I look at the wire schematic for the PM 1000 intercom, it indicates
>that I should "connect the shields at intercom only".
>My question is: Should I use the shield wire as the ground on both ends in
>the mic and headphone connections?
First, when instructions and schematics for any product are
specific as to how shields should be handled, follow the
instructions. A shield need be connected one-end only
in order to be an effective shield. A shield may also
DOUBLE as one of the signal conductors in the system
and may be connected at both ends. When this is
technique is used by the manufacturer for the accessory
you're installing, their installation instructions
will be specific as to how shields are treated.
In the case of the PM1000, the wiring diagram they
posted at:
http://www.ps-engineering.com/docs/PM1000IISpecial.pdf
is quite specific for not using shields as signal return
path for components remote to the intercom. I can tell you
that a shielded, twisted pair will nicely substitute for
the shielded trio and you can then use the shield as
ground return for the microphone jacks. An example of this
wiring is illustrated in the schematic for the radio harness
I used to build for the Microair 760 which you can see
on page 2.1 of the schematics in:
http://www.aeroelectric.com/Catalog/avionics/760imB.pdf
Either way will work. The prohibition is for connecting
signal returns to ground system at both ends . . . whether
the signal return is a separate wire under the shield -OR-
the shield itself. Use insulating bushings at the mic and
headset jacks if they're installed on metalic brackets
that are bolted to the airframe.
Bob . . .
Message 19
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| Subject: | Re: Ground and braded wire. |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 12:39 PM 12/14/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: John <m2mustang@yahoo.com>
>
>No. It's my understanding that the shield will cease
>to be a shield if it's connected at both ends.
>Only effective when terminated at the end indicated.
Not true. Greg tried to perpetuate this myth in
is one-size-fits-all guide for wiring airplanes.
When I asked him to discuss the simple-ideas
behind the uses of shield conductors, he ignored
the questions.
A shield will work perfectly well to protect interior
wires from the ravages of fast risetime noises in
other conductors while simultaneously serving
as one of the signal lines.
Bob . . .
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