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1. 08:02 AM - Re: Shielded wiring for P leads (FLYaDIVE)
2. 06:18 PM - Re: Shielded wiring for P leads (Noel Loveys)
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| Subject: | Re: Shielded wiring for P leads |
Nole:
You must have the name spelled wrong because I was not able
to research anything on that name (Reg Fressenden). Marconi was given much
of the credit for the discovery of radio transmission ONLY because
he had money backing him and had a stage prescense.
Hertz, did a lot of teaching and lectures but his ideas were not widely
accepted, only because he did not produce as many or as elaborate a device.
Many years later they finally gave him the reconion he deserved and change
d
the basic unit of frequency from the Cycle to HERTZ.
As I mentioned and you reiterated the first transmitters did use Spark Gaps
.
But what you are referring to with the generator (not alternator) came
years later. It was know as a Rotary Spark Gap. The thought --- THOUGHT
--- Was that the speed of the Rotary Spark Gap would control the frequency
-
Well, ANYTHING that turns on and off at a regular rate does have a frequenc
y
but was NOT the controlling factor. Marconi made the same mistake. That i
s
where Hertz came in. Marconi wanted to make transatlantic communication an
EVERYDAY event. Everyday in the ability to send a radio wave any time he
wished. So he made bigger and bigger - Higher and Higher antennas. The
bigger he went the less his chances of transatlantic communications became.
Do you see where I am going?
Hertz said make them smaller... The LENGTH of the antenna was and still is
the controlling factor - FREQUENCY.
As a HAM you should remember the formula:
L (in meters) = 300,000,000 / Freq (in MHz). That is a basic PHYSICS
formula. So:
Freq = 300,000,000 / L (aka *299,792,458 meters per second = speed o
f
light)*
So, what did the Rotary Spark Gap do?
It created a longer lasting spark - Almost a continuous spark. Because the
spark had to travel down the Antenna (wire) and then Radiate Out on a
Frequency determined by the Length of the Antenna (Aerial) Oh! They did no
t
have Antennas in those days.
Of Course - The frequency was no where accurate. It was a Very, Very Wide
Band.
Now, how do I know all this trivia? I made a 300,0000 Volt Spark Gap
Transmitter using a series of three neon sign AUTOTRANSFORMER'S. Found one
alone worked better than all three.
Back to Ground Planes - As I said in my original post we are discussing VHF
frequencies. Sure at the high end of VHF and of course in UHF and (SHF)
Microwave Shields can radiate. But we are not talking those frequencies.
And if we were other procedures would be used. Not for this discussion.
So, here is the other formula you should be acquainted with:
L (in feet) = 468/Freq (in MHz) this of course is for a dipole but divide
that by 2 and you have a vertical. Verticals are what 98.76% of our planes
use. <--- percentage data PFMA.
This will show that the length required for your 1/4wave... BUT! Wait a
second. RF is Grounded at BOTH ends. AF is grounded at the source. So
where is this magical RF coming down a AF line AND if it did, because of
poor installation then it would have to be inductively coupled (Capacitive
-
No Way at our frequencies) AND there are so many reasons why that would not
happen either. Power being #1.
And finally to respond to our not so geek minded friend. The reason why
I perused this long (I'm sorry) discussion is to KILL the misconceptions an
d
Old Wives Tails that are so easily propagated over the internet. ALL sorts
of oral defecation propagate faster than the TV - Radio and especially the
New Paper. While Noel is well meaning in his post the information is not
correct, close but no cigar. And as YOU mentioned we are trying to HELP th
e
fellow asking the question. Incorrect information does not help.
I'm off. Must go flying now - In a static free plane.
Barry
On Fri, Sep 24, 2010 at 10:25 AM, Noel Loveys <noelloveys@yahoo.ca> wrote:
> Ok Barry I=92ll bite.
>
> I=92m not sure about this one...
>
> For phone, in the earliest part of the twentieth century Reg Fressenden,
a
> Canadian had a transmitter set up in Connecticut. He used a generator
> (Anderson alternator) with many poles and running at extremely, for the d
ay,
> high speeds to develop the frequency he wanted for the first broadcast
> radio. If memory serves me right on his first test the darn thing blew u
p
> on the first trial but he had a back up for his first transmission connec
ted
> to his antenna. That makes him the inventor of radio as we know it today
.
>
>
> The earliest Morse code transmitters used spark gaps. The system was a
> muther of a coil attached to as much dc voltage as they could muster and
a
> key wired in series. The secondary coil as connected to what is essentia
lly
> a spark gap and a tank circuit to amplify only one frequency. Problems
> abounded. As the spark electrodes heated up the width of the spark chang
ed,
> the batteries ran down and one tank is not enough filtration/tuning so sp
ark
> transmitters are noisy all over the bands. A long time before I became
> involved in Amateur Radio spark transmitters became illegal but there are
> always a few around who will try them. Then again there are lots of
> unlicensed operators on the bands.
>
>
> BTW I have been to but not operated the radio station at the receive site
> of the world=92s first trans Atlantic broadcast.... it was only a resoun
ding
> letter =93S=94 picked up by an antenna actually flown aloft by a kite. M
y two
> most favourite things, flying and Radio.
>
>
> Ground planes not just happening you are right they are constructed but n
ot
> always intentionally. You are also right that the shield is not a ground
> plane. However ground planes can occur when grounded shields are attache
d
> to metallic bodies at the end remote from the source.. especially if one
of
> those bodies happens to be =BC wavelength the com frequency as can easily
> happen in the panel of one of our small planes.
>
>
> As for reinventing the wheel... Why not? Here it is complete with bent
> spokes ;-) http://www.gizmag.com/go/3603/
>
>
> Noel
>
> *From:* owner-jabiruengine-list-server@matronics.com [mailto:
> owner-jabiruengine-list-server@matronics.com] *On Behalf Of *FLYaDIVE
> *Sent:* September 23, 2010 7:25 PM
>
> *To:* jabiruengine-list@matronics.com
> *Subject:* Re: JabiruEngine-List: Shielded wiring for P leads
>
>
> Noel:
>
>
> Please read my responses within the body of your post.
>
>
> Barry
>
> On Thu, Sep 23, 2010 at 3:54 PM, Noel Loveys <noelloveys@yahoo.ca> wrote:
>
> Mark:
>
>
> The EMI given off by P leads is hardly at RF frequencies as the sound is
> actually generated by the mags
>
>
> [Barry] - There SURE IS RF given off by a Mag. How? Well when
> the points OPEN they create a SPARK... The Spacing of the Points is know
as
> a Spark Gap... A.K.A. Spark Gap Transmitter... It is the exact same thing
> Hertz and Marconi experimented with way back in the days of "The Eiather"
.
> So YES, Mark and Noel you sure do want to Shield and Ground Both Ends.
>
> LOADED QUESTION Noel: Back in the day what did they use to control the
> Frequency?
>
>
> or alternator both of which are well into audio frequency. Even to
> shield a wire from RFI grounding at one end prevents the accidental
> construction of a ground plane
>
>
> [Barry] - Ground planes don't just happen ... Especially like in the
> above explanation
>
> A ground plane is Frequency, Length, Area and Distance dependent. A shie
ld
> is NOT a ground plane..
>
>
> at the end furthest from the source. Even when wiring very complex
> panels in large aircraft shielded wires are generally shielded only at th
e
> source end.
>
>
> [Barry] - Gaggle - Please go back and read my post on the RULES of
> Grounding and Shielding.
>
> THEY WORK!
>
> Shielding is broken down into AF & RF. That is all I'm going to say for
> now. Please Read My Post.
>
>
> Let's not re-invent the wheel. Especially with bend spokes.
>
>
> Barry
>
> E.E. & M.E.
>
>
> For example; The mic wire which comes from the transceiver to the audio
> panel should only have the shield grounded at the Transceiver end. The m
ic
> wire that goes from the audio panel to the pilot/co-pilot jacks (they are
> different) will have the shield grounded at the audio panel. The mic cor
d
> itself is grounded through the shield attached to the base ring of the ja
ck.
>
>
> All that takes care of stray RF getting into the Mic system (hopefully ;-
D)
> but then there are the EMI sounds that can get into the DC source to the
> radios. This EMI is things like alternator noise and ignition noise. Ag
ain
> to prevent shielded wire from becoming a capacitive bridge into the DC po
wer
> wires for the radios it is normally only shield grounded at the source
> (close to the generator) end.
>
>
> With some of these systems you may actually come across a situation where
> an extra ground will protect a system... just don=92t ask anyone to expl
ain
> why.
>
>
> Some sources of EMI and there are a lot more than I can list here
>
>
> Fouled spark plugs, Worn crystallized plug wires, worn capacitors in the
> alternator, Poor grounding on an ECU, Poor grounding of the engine case t
o
> the electrical circuit, Poorly grounded strobe system, Poor grounding of
the
> radio stack, poor grounding of the braid at the antenna end of feed coax.
> Gee it=92s surprising how many times grounding comes up. Rahter than hav
ing
> added grounds going willy-nilly I think it=92s better to make sure the on
es
> installed and which worked for sometimes years are all clean. To clean
> these grounds you must disconnect them, clean the contact areas and reatt
ach
> them. Looking at a connection doesn=92t count.
>
>
> While you are at it why not make a diagram of the wiring of your plane.
> Just a simple block diagram will do. Show the colours of the wires, the
> connection plugs and where all the grounds are. Such a diagram will make
> future troubleshooting a whole lot easier both for yourself and future
> owners of your plane. Put all your diagrams in your aircraft (log) book
so
> you can find it easily.
>
>
> Noel
>
>
> *From:* owner-jabiruengine-list-server@matronics.com [mailto:
> owner-jabiruengine-list-server@matronics.com] *On Behalf Of *Mark
> Hubelbank
> *Sent:* September 21, 2010 10:47 AM
> *To:* jabiruengine-list@matronics.com
> *Subject:* JabiruEngine-List: Shielded wiring for P leads
>
>
> To all working with noise in aircraft wiring. I have been following the
> listings on the subject of shielding and as a design engineer, I have one
> thing to add (without the intent of generating any controversy).
>
> This may help in cases where noise is comming from the ignition "P" leads
> which run from the mags to the ignition key switch. There is a lot of tal
k
> on grounding one end vers both ends of a shield. When one is working with
a
> RF situation, one needs to ground both ends otherwise the shield will sim
ple
> pick up the signal from the center conductor and act as an antenna itself
.
> After all an antenna at VHF frequencies is simply a short wire connected
at
> one end. In the case of the "P" leads, you may be radiating RF energy pic
ked
> up from the mags into the instrument panel area, exactly where you really
> don't want it.
>
> Thus when trying to prevent RF from "leaking" out, one needs to ground th
e
> shield at both ends. This is more problematic in a composite aircraft and
> other measures may be needed at the instrument panel end if there is noth
ing
> to ground to. In those cases, some other RF tricks may be required. I hav
e
> not actually had to "de-noise" such an installation but I would first try
a
> combination of terminations (50 ohm carbon resistor in series with 0.001
uf
> ceramic cap - very short leads from shield to center conductor) and ferr
ite
> suppressors on the wire. Also note that by using wire that has high loss
at
> VHF some of the conducted interference is attenuated. Typically non-coax
> shielded wire (MIL-C-27500) is in this class.
>
> Note that the connect shield at one end logic was originated to deal with
> low frequency issues like ground loops. An even better solution in some o
f
> those cases is to float the device at one end. For example for a micropho
ne
> lead, one can use insulating washers to separate the jack from the airfra
me
> and then use the shield to provide the return path. This is the best way
to
> go when possible. All this is mentioned to various degrees in the literat
ure
> but I thought it does not hurt to give the example.
>
> --
>
> Mark Hubelbank
>
> NorthEast Monitoring
>
> 2 Clock Tower Place
>
> Suite 555
>
> Maynard, MA, 01754 - USA
>
> mhubel@nemon.com
>
> 978-443-3955
>
> * *
>
> * *
>
> *ist" target="_blank">http://www.matronics.com/Navigator?JabiruEngine-L
ist*
>
> * *
>
> *tp://forums.matronics.com*
>
> *_blank">http://www.matronics.com/contribution*
>
> * *
>
>
> * *
>
> * *
>
> **
>
> **
>
> **
>
> **
>
> **
>
> **
>
> *http://www.matronics.com/Navigator?JabiruEngine-List*
>
> **
>
> **
>
> **
>
> *http://forums.matronics.com*
>
> **
>
> **
>
> **
>
> **
>
> *http://www.matronics.com/contribution*
>
> **
>
> * *
>
> *
>
===========
===========
===========
===========
> *
>
>
Message 2
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| Subject: | Shielded wiring for P leads |
Bonne Vol
Noel
From: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of
FLYaDIVE
Sent: September 26, 2010 12:27 PM
Subject: Re: JabiruEngine-List: Shielded wiring for P leads
Nole:
You must have the name spelled wrong because I was not able to research
anything on that name (Reg Fressenden). Marconi was given much of the
credit for the discovery of radio transmission ONLY because he had money
backing him and had a stage prescense.
Hertz, did a lot of teaching and lectures but his ideas were not widely
accepted, only because he did not produce as many or as elaborate a
device.
Many years later they finally gave him the reconion he deserved and
changed
the basic unit of frequency from the Cycle to HERTZ.
As I mentioned and you reiterated the first transmitters did use Spark
Gaps.
But what you are referring to with the generator (not alternator) came
years
later. It was know as a Rotary Spark Gap. The thought --- THOUGHT ---
Was
that the speed of the Rotary Spark Gap would control the frequency -
Well,
ANYTHING that turns on and off at a regular rate does have a frequency
but
was NOT the controlling factor. Marconi made the same mistake. That is
where Hertz came in. Marconi wanted to make transatlantic communication
an
EVERYDAY event. Everyday in the ability to send a radio wave any time
he
wished. So he made bigger and bigger - Higher and Higher antennas. The
bigger he went the less his chances of transatlantic communications
became.
Do you see where I am going?
Hertz said make them smaller... The LENGTH of the antenna was and still
is
the controlling factor - FREQUENCY.
As a HAM you should remember the formula:
L (in meters) = 300,000,000 / Freq (in MHz). That is a basic PHYSICS
formula. So:
Freq = 300,000,000 / L (aka 299,792,458 meters per second = speed
of
light)
So, what did the Rotary Spark Gap do?
It created a longer lasting spark - Almost a continuous spark. Because
the
spark had to travel down the Antenna (wire) and then Radiate Out on a
Frequency determined by the Length of the Antenna (Aerial) Oh! They did
not
have Antennas in those days.
Of Course - The frequency was no where accurate. It was a Very, Very
Wide
Band.
Now, how do I know all this trivia? I made a 300,0000 Volt Spark Gap
Transmitter using a series of three neon sign AUTOTRANSFORMER'S. Found
one
alone worked better than all three.
Back to Ground Planes - As I said in my original post we are discussing
VHF
frequencies. Sure at the high end of VHF and of course in UHF and (SHF)
Microwave Shields can radiate. But we are not talking those
frequencies.
And if we were other procedures would be used. Not for this discussion.
So, here is the other formula you should be acquainted with:
L (in feet) = 468/Freq (in MHz) this of course is for a dipole but
divide
that by 2 and you have a vertical. Verticals are what 98.76% of our
planes
use. <--- percentage data PFMA.
This will show that the length required for your 1/4wave... BUT! Wait a
second. RF is Grounded at BOTH ends. AF is grounded at the source. So
where is this magical RF coming down a AF line AND if it did, because of
poor installation then it would have to be inductively coupled
(Capacitive -
No Way at our frequencies) AND there are so many reasons why that would
not
happen either. Power being #1.
And finally to respond to our not so geek minded friend. The reason why
I
perused this long (I'm sorry) discussion is to KILL the misconceptions
and
Old Wives Tails that are so easily propagated over the internet. ALL
sorts
of oral defecation propagate faster than the TV - Radio and especially
the
New Paper. While Noel is well meaning in his post the information is
not
correct, close but no cigar. And as YOU mentioned we are trying to HELP
the
fellow asking the question. Incorrect information does not help.
I'm off. Must go flying now - In a static free plane.
Barry
On Fri, Sep 24, 2010 at 10:25 AM, Noel Loveys <noelloveys@yahoo.ca>
wrote:
Ok Barry I=92ll bite.
I=92m not sure about this one...
For phone, in the earliest part of the twentieth century Reg Fressenden,
a
Canadian had a transmitter set up in Connecticut. He used a generator
(Anderson alternator) with many poles and running at extremely, for the
day,
high speeds to develop the frequency he wanted for the first broadcast
radio. If memory serves me right on his first test the darn thing blew
up
on the first trial but he had a back up for his first transmission
connected
to his antenna. That makes him the inventor of radio as we know it
today.
The earliest Morse code transmitters used spark gaps. The system was a
muther of a coil attached to as much dc voltage as they could muster and
a
key wired in series. The secondary coil as connected to what is
essentially
a spark gap and a tank circuit to amplify only one frequency. Problems
abounded. As the spark electrodes heated up the width of the spark
changed,
the batteries ran down and one tank is not enough filtration/tuning so
spark
transmitters are noisy all over the bands. A long time before I became
involved in Amateur Radio spark transmitters became illegal but there
are
always a few around who will try them. Then again there are lots of
unlicensed operators on the bands.
BTW I have been to but not operated the radio station at the receive
site of
the world=92s first trans Atlantic broadcast.... it was only a
resounding
letter =93S=94 picked up by an antenna actually flown aloft by a kite.
My two
most favourite things, flying and Radio.
Ground planes not just happening you are right they are constructed but
not
always intentionally. You are also right that the shield is not a
ground
plane. However ground planes can occur when grounded shields are
attached
to metallic bodies at the end remote from the source.. especially if one
of
those bodies happens to be =BC wavelength the com frequency as can
easily
happen in the panel of one of our small planes.
As for reinventing the wheel... Why not? Here it is complete with bent
spokes ;-) http://www.gizmag.com/go/3603/
Noel
From: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of
FLYaDIVE
Sent: September 23, 2010 7:25 PM
Subject: Re: JabiruEngine-List: Shielded wiring for P leads
Noel:
Please read my responses within the body of your post.
Barry
On Thu, Sep 23, 2010 at 3:54 PM, Noel Loveys <noelloveys@yahoo.ca>
wrote:
Mark:
The EMI given off by P leads is hardly at RF frequencies as the sound is
actually generated by the mags
[Barry] - There SURE IS RF given off by a Mag. How? Well when the
points
OPEN they create a SPARK... The Spacing of the Points is know as a Spark
Gap... A.K.A. Spark Gap Transmitter... It is the exact same thing Hertz
and
Marconi experimented with way back in the days of "The Eiather" . So
YES,
Mark and Noel you sure do want to Shield and Ground Both Ends.
LOADED QUESTION Noel: Back in the day what did they use to control the
Frequency?
or alternator both of which are well into audio frequency. Even to
shield a
wire from RFI grounding at one end prevents the accidental construction
of a
ground plane
[Barry] - Ground planes don't just happen ... Especially like in the
above
explanation
A ground plane is Frequency, Length, Area and Distance dependent. A
shield
is NOT a ground plane..
at the end furthest from the source. Even when wiring very complex
panels
in large aircraft shielded wires are generally shielded only at the
source
end.
[Barry] - Gaggle - Please go back and read my post on the RULES of
Grounding
and Shielding.
THEY WORK!
Shielding is broken down into AF & RF. That is all I'm going to say for
now. Please Read My Post.
Let's not re-invent the wheel. Especially with bend spokes.
Barry
E.E. & M.E.
For example; The mic wire which comes from the transceiver to the audio
panel should only have the shield grounded at the Transceiver end. The
mic
wire that goes from the audio panel to the pilot/co-pilot jacks (they
are
different) will have the shield grounded at the audio panel. The mic
cord
itself is grounded through the shield attached to the base ring of the
jack.
All that takes care of stray RF getting into the Mic system (hopefully
;-D)
but then there are the EMI sounds that can get into the DC source to the
radios. This EMI is things like alternator noise and ignition noise.
Again
to prevent shielded wire from becoming a capacitive bridge into the DC
power
wires for the radios it is normally only shield grounded at the source
(close to the generator) end.
With some of these systems you may actually come across a situation
where an
extra ground will protect a system... just don=92t ask anyone to
explain why.
Some sources of EMI and there are a lot more than I can list here
Fouled spark plugs, Worn crystallized plug wires, worn capacitors in the
alternator, Poor grounding on an ECU, Poor grounding of the engine case
to
the electrical circuit, Poorly grounded strobe system, Poor grounding of
the
radio stack, poor grounding of the braid at the antenna end of feed
coax.
Gee it=92s surprising how many times grounding comes up. Rahter than
having
added grounds going willy-nilly I think it=92s better to make sure the
ones
installed and which worked for sometimes years are all clean. To clean
these grounds you must disconnect them, clean the contact areas and
reattach
them. Looking at a connection doesn=92t count.
While you are at it why not make a diagram of the wiring of your plane.
Just a simple block diagram will do. Show the colours of the wires, the
connection plugs and where all the grounds are. Such a diagram will
make
future troubleshooting a whole lot easier both for yourself and future
owners of your plane. Put all your diagrams in your aircraft (log) book
so
you can find it easily.
Noel
From: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of Mark
Hubelbank
Sent: September 21, 2010 10:47 AM
Subject: JabiruEngine-List: Shielded wiring for P leads
To all working with noise in aircraft wiring. I have been following the
listings on the subject of shielding and as a design engineer, I have
one
thing to add (without the intent of generating any controversy).
This may help in cases where noise is comming from the ignition "P"
leads
which run from the mags to the ignition key switch. There is a lot of
talk
on grounding one end vers both ends of a shield. When one is working
with a
RF situation, one needs to ground both ends otherwise the shield will
simple
pick up the signal from the center conductor and act as an antenna
itself.
After all an antenna at VHF frequencies is simply a short wire connected
at
one end. In the case of the "P" leads, you may be radiating RF energy
picked
up from the mags into the instrument panel area, exactly where you
really
don't want it.
Thus when trying to prevent RF from "leaking" out, one needs to ground
the
shield at both ends. This is more problematic in a composite aircraft
and
other measures may be needed at the instrument panel end if there is
nothing
to ground to. In those cases, some other RF tricks may be required. I
have
not actually had to "de-noise" such an installation but I would first
try a
combination of terminations (50 ohm carbon resistor in series with 0.001
uf
ceramic cap - very short leads from shield to center conductor) and
ferrite
suppressors on the wire. Also note that by using wire that has high loss
at
VHF some of the conducted interference is attenuated. Typically non-coax
shielded wire (MIL-C-27500) is in this class.
Note that the connect shield at one end logic was originated to deal
with
low frequency issues like ground loops. An even better solution in some
of
those cases is to float the device at one end. For example for a
microphone
lead, one can use insulating washers to separate the jack from the
airframe
and then use the shield to provide the return path. This is the best way
to
go when possible. All this is mentioned to various degrees in the
literature
but I thought it does not hurt to give the example.
--
Mark Hubelbank
NorthEast Monitoring
2 Clock Tower Place
Suite 555
Maynard, MA, 01754 - USA
mhubel@nemon.com
978-443-3955
ist"
target="_blank">http://www.matronics.com/Navigator?JabiruEngine-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
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