Electromagnetic field compensated cable

An electromagnetic field compensated cable having an electrically insulating casing (20, 40, 50) includes a structure (21-22, 41, 51) that effects cancellation of electric and/or magnetic field components due to current flow through the cable. One configuration includes a central twisted pair of insulated leads (21, 22) wherein only one end of each of the leads (23, 24) is terminated in a connector (25, 26). Another configuration has a central structure of conductive wire of alternating rectangular shape. (41, 51).

DESCRIPTION 
1. Technical Field 
This invention is in the field of high voltage distribution cables, and in 
particular such high voltage cables as are utilized in engine ignition 
systems. 
2. Background Art 
Prior art engine ignition cables of the high voltage type utilize hard wire 
conductors embedded in an electrical insulation or utilize a carbon or 
other high resistance conductors. 
The hard wire embedded conductor cable provides substantially no 
attenuation of ignition current that it supplies to the engine's 
electrical igniter, but produces large electromagnetic fields that cause 
noise to be induced in the antenna of an automotive receiver. 
The carbon or other high resistance embedded conductor cable is generally 
of the order of 15,000 ohms DC resistance. Whereas such high resistance 
reduces the electromagnetic radiation, it nevertheless causes substantial 
reduction of ignition current in the secondary high voltage ignition 
transformer circuit and hence causes a substantial decrease in electrical 
energy delivered to the igniter. 
DISCLOSURE OF INVENTION 
It is an objective of this invention to provide means for conducting high 
transient currents between the ignition transformer secondary winding 
output and the igniters without any substantial quantity of 
electromagnetic energy coupling into the radio receiver antenna of an 
automotive installation. 
It is another objective of this invention to reduce the circuit reactance 
of the combination of ignition transformer secondary winding and the high 
voltage cables coupling the secondary to the igniters. 
It is still another objective of this invention to create a high voltage 
distributed capacity cable which by its own structure cancels its own 
generated electric and magnetic field components so as to minimize 
electromagnetic radiation therefrom. 
Accordingly, a high voltage cable is constructed utilizing a pair of 
twisted or transposed turns of electrically insulated wires wherein one 
end of each of the wires remains unterminated, and the other ends of each 
wire is terminated in a connector in conventional manner. Thus, the result 
is distributed capacity coupling between these wires over the entire 
length of the cable. In its use in ignition circuits, this cable permits 
an increased ignition current flow due to reduced circuit reactance, since 
the capacitive reactance of the cable compensates for the inductive 
reactance of the ignition transformer secondary winding. The transposition 
of the pair of wires results in cancellation of magnetic field components 
along the cable length and cancellation of electric field components 
between such wire pair.

DETAILED DESCRIPTION OF BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, a high voltage cable 10, for general purposes usage, 
but also having utilization in an ignition circuit of an automotive 
system, takes advantage of the principle of distributed capacity between a 
pair of twisted or transposed wires to provide capacitive coupling of an 
ignition transformer secondary winding through a high voltage distributor 
to connect an igniter thereto. 
Cable 10 comprises a pair of twisted or transposed pair of insulated wires 
21 and 22. The insulation on these wires provides the requisite dielectric 
material such as polytetrafluorethylene (trade name of TEFLON) between the 
inner conductors 23 and 24 respectively of these wires electrically 
terminating at connectors 25 and 26 respectively. The opposite ends of 
each of these wires are unterminated so that a continuous distributed 
capacity is realized over the length of the cable. The pitch of the 
transposed wires over each other is not critical but should be as tight or 
as close together as possible. Each of wires 21 and 22 may have center 
conductors of about number 20 gauge with a Teflon insulation thereover. 
Connector 25 has at least one slit 27 therein and connector 26 also has at 
least one slit 28 therein to provide the necessary flexibility in the 
connectors so that this cable can be connected between one of the 
distributor ports and the center electrode terminal of one of the 
igniters. A similar cable with suitable connectors may be used to make 
connection between the high voltage port of the ignition transformer 
secondary winding and the center distributor port. 
A suitable electrical insulation material 20 covers and molds therein wire 
pair 21-22, which material 20 is also molded to connectors 25 and 26. An 
electrically insulating cup 29 is generally used to hold connector 25 of 
this cable secure in one of the distributor ports, and a rather 
thick-walled and long sleeve 30 of high quality high voltage insulating 
material is used over a portion of the cable to hold connector 26 secure 
to the center electrode terminal of the igniter, also partially covering 
the ceramic insulator of the igniter in order to reduce voltage arcs and 
corona formation external to and in proximity of the igniter when 
extremely high voltages and currents are utilized by the ignition system 
in which this cable is installed. 
Referring to FIG. 2, an electrical equivalent circuit of wires 21 and 22 
and their respective terminations at 23 and 24 are shown having a number 
of transposed turns of wire as wound in FIG. 1 configuration. Each of the 
turns of wire are shown illustratively expanded and in particular largely 
expanded in their vertical dimension in the drawing so that the 
electromagnetic field components can be ascertained and illustrated. 
Assuming at one instant of time that termination 23 of wire 21 is at a 
positive potential and termination 24 of wire 22 is at a negative 
potential with respect to the potential at 23 due to ignition current flow 
comprising displacement current components i1, i2, i3, i4, i5, i6 created 
by their respective electric field components E1, E2, E3, E4, E5, E6, it 
can be seen that cable 10 as structured acts as a distributed capacitor 
with theoretically infinite number of capacitive elements traversing the 
length of wires 21-22. As an example, since electric field vector E1 will 
be established in a direction from the positively charged wire 21 to the 
negatively charged wire 22, electric field vector E2 will also be 
established in a direction from its positively charged wire to its 
negatively charged wire, but due to wire transposition, vector E3 will be 
in a direction opposite to vector E1. Hence, currents i1 and i2 will be 
displaced in a direction between their positive and negative source 
potentials, namely wires 21 and 22 in the same direction as their electric 
field components. Consequently, although the electric field vectors will 
change in direction with every turn of wire, and thereby cancel each 
other, the displacement currents will pass between wires 21 and 22 in 
similar manner as displacement current transfers between plates of a 
capacitor in a manner well documented by Maxwell's equations. It is well 
known that ignition current is a complex transient wave which a capacitor 
will pass readily. 
Applying the right hand rule of current and magnetic field directions, it 
can be seen from the diagram that magnetic field vector component H1 will 
be perpendicular to current component i1, and that magnetic field vector 
component H2 will be perpendicular to current component direction i2. 
Since displacement current i1 is in opposite directions to displacement 
current i2 the direction of vector H1 will be opposite to the direction of 
vector H2 and of equal magnitude, thus cancelling each other insofar as 
inducing a magnetic field into the antenna of the ratio receiver. In 
similar manner H3 will be cancelled by H4, and H5 will be cancelled by H6. 
It is pointed out that the magnetic fields were simply illustrated in a 
single plane whereas in actuality such fields are circumferential to the 
cable consisting of wires 21-22, with field components that cancel each 
other everywhere along the length of the cable. 
Only two turns or wire transpositions were illustrated in FIG. 1 for 
largeness and clarity. In actual practice, four type 10 cables were 
constructed and tested for their ability to deliver increased current to 
the igniters, as measured by suitable instrumentation and also visibly 
observing the arc intensities across the igniter bases using a suitable 
test fixture therefor. Cables having lengths of 1.5, 2.0, 2.5 and 3.0 feet 
were constructed. There was little difference in ignition current 
magnitudes between the system utilizing any of the four cable lengths 
indicating that the total capacitive magnitudes may be broad over the 
range of frequencies encountered in an ignition transient current wave. 
However, the ignition current increased approximately 2.5 times over the 
current experienced with the usage of a hard copper wire center conductor 
cable. 
Referring to FIG. 3, the cables of FIGS. 1, 4 and 5 may have a wire 31 
wound over the outer surfaces of any of these cables, and such wire 
grounded either at one or both ends. This will eliminate any minute stray 
electromagnetic radiation caused by structural imballance of the turns in 
any of these cables. 
Referring to FIG. 4, electrical conductor 41 is formed in generally 
rectangular shaped configuration and such conductor is molded within 
tubular insulator 40. One end of conductor 41 is electrically joined to a 
connector 25 similar to a like connector shown in FIG. 1, and the other 
end of conductor 41 is electrically joined to a connector 26 similar to a 
like connector illustrated by FIG. 1. If conductor 41 is electrically 
insulated, then the adjacent vertical portions as illustrated in the 
figure could abut each other, thereby minimizing the lengths of the 
horizontal portions of this conductor. Such closely-spaced format is 
desireable in that the magnetic field components in this structure of 
horizontal direction are additive and therefore it is desireable to 
maintain them as small as possible. On the other hand, the magnetic field 
components of adjacent vertical portions are in opposite directions in 
view of the current flow directions in such adjacent vertical portions, to 
cause cancellation of all vertical magnetic field components. Connectors 
as used in FIG. 1 configuration are also used for this configuration. 
Referring to FIG. 4, electrical conductor 51 is formed in generally 
rectangular shaped configuration and such conductor is molded within 
insulator 50. One end of conductor 51 is electrically joined to a 
connector 25 similar to a like connector shown in FIG. 1, and the other 
end of conductor 51 is electrically joined to a connector 26 similar to a 
like connector illustrated by FIG. 1. If conductor 51 is electrically 
insulated, then the adjacent vertical portions as illustrated in the 
figure could abut each other, thereby minimizing the lengths of the 
horizontal portions of this conductor. Such closely-spaced format is 
desireable in that the magnetic field components in this structure of 
horizontal direction are additive and therefore it is desireable to 
maintain them as small as possible. On the other hand, the magnetic field 
components of adjacent vertical portions are in opposite directions in 
view of the current flow directions in such adjacent vertical portions, to 
cause cancellation of all vertical magnetic field components. Connectors 
as used in FIG. 1 configuration are also used for this configuration.