Effect of twisting on twisted pair impedance.
 

Hello,

Following link http://qucs.sourceforge.net/tech/node93.html gives an
expression for the characteristic impedance of a twisted pair. It also
includes a correction on effective permittivity for the twist angle
(or twists/length).

I have a document from Universidad de Buenos Aires, www.fi.uba.ar,
"Líneas de transmisión" (transmission lines) this document explicitly
mentions that the twist angle must be in radians.

However, when assuming twist angle of 45 degrees (0.785 radians, that
is tight twisting) and a relative epsilon of 3, the formula gives a
decrease of Z0 of less then 0.1% (w.r.t. almost no twisting). This
result doesn't match my experience and experimental data from other
recourses.

When entering 45 degrees, the result is a reduction of Z0 to 70% of
non-twist value, which sounds better to me.

Does somebody have access to the original document (or know from
experience) to figure out whether radians or degrees must be used for
the formulas in the link mentioned above?

Thanks,

Wim
PA3DJS
www.tetech.nl
Please remove abc from the address in case of direct reply.

Effect of twisting on twisted pair impedance.
 

Wimpie wrote:
Hello,

Following link http://qucs.sourceforge.net/tech/node93.html gives an
expression for the characteristic impedance of a twisted pair. It also
includes a correction on effective permittivity for the twist angle
(or twists/length).

They cite the 1971 paper by Lefferson...

Lefferson gives T = tan(theta)/(pi *D)
where T = twist per unit length
theta is "pitch angle" (between wire and line down center of TL)
D is center to center spacing.

he observes that the maximum angle is on the order of 50.5 degrees,
where the wire will tend to break, and that optimum performance is
angles from 20-45 degrees.

Figure 6 in that paper gives the picture... (an angle of zero would be
something like twinlead)

he gives a formula for the actual wire length.. one twist is
pi*D*sqrt(1+1/(tan(theta)^2))

There are some typos in the original paper (Figure 6 and Eq 12).. in the
IEEE Xpress online version, they've been fixed.


I have a document from Universidad de Buenos Aires, www.fi.uba.ar,
"Líneas de transmisión" (transmission lines) this document explicitly
mentions that the twist angle must be in radians.

Since figure 2 in the Lefferson paper gives angles in degrees, I assume
that the empirical expression (cited on the QUCS page) is the same as
Lefferson's equation [7] beta=0.25 +4E-4*theta^2


However, when assuming twist angle of 45 degrees (0.785 radians, that
is tight twisting) and a relative epsilon of 3, the formula gives a
decrease of Z0 of less then 0.1% (w.r.t. almost no twisting). This
result doesn't match my experience and experimental data from other
recourses.

When entering 45 degrees, the result is a reduction of Z0 to 70% of
non-twist value, which sounds better to me.


Does somebody have access to the original document (or know from
experience) to figure out whether radians or degrees must be used for
the formulas in the link mentioned above?

Thanks,

Wim
PA3DJS
www.tetech.nl
Please remove abc from the address in case of direct reply.

Effect of twisting on twisted pair impedance.
 

On 15 abr, 00:39, Jim Lux wrote:
Wimpie wrote:
Hello,

Following linkhttp://qucs.sourceforge.net/tech/node93.htmlgives an
expression for the characteristic impedance of a twisted pair. It also
includes a correction on effective permittivity for the twist angle
(or twists/length).

They cite the 1971 paper by Lefferson...

Lefferson gives T = tan(theta)/(pi *D)
where T = twist per unit length
theta is "pitch angle" (between wire and line down center of TL)
D is center to center spacing.

he observes that the maximum angle is on the order of 50.5 degrees,
where the wire will tend to break, and that optimum performance is
angles from 20-45 degrees.

Figure 6 in that paper gives the picture... (an angle of zero would be
something like twinlead)

he gives a formula for the actual wire length.. one twist is
pi*D*sqrt(1+1/(tan(theta)^2))

There are some typos in the original paper (Figure 6 and Eq 12).. in the
IEEE Xpress online version, they've been fixed.



I have a document from Universidad de Buenos Aires,www.fi.uba.ar,
"Líneas de transmisión" (transmission lines) this document explicitly
mentions that the twist angle must be in radians.

Since figure 2 in the Lefferson paper gives angles in degrees, I assume
that the empirical expression (cited on the QUCS page) is the same as
Lefferson's equation [7] beta=0.25 +4E-4*theta^2



However, when assuming twist angle of 45 degrees (0.785 radians, that
is tight twisting) and a relative epsilon of 3, the formula gives a
decrease of Z0 of less then 0.1% (w.r.t. almost no twisting). This
result doesn't match my experience and experimental data from other
recourses.

When entering 45 degrees, the result is a reduction of Z0 to 70% of
non-twist value, which sounds better to me.

Does somebody have access to the original document (or know from
experience) to figure out whether radians or degrees must be used for
the formulas in the link mentioned above?

Thanks,

Wim
PA3DJS
www.tetech.nl
Please remove abc from the address in case of direct reply.

Hello Jim,

Thank you for your helpful reply.

I think I can be sure now that the twist angle must be entered in
degrees rather then radians.

Best regards,

Wim
PA3DJS
www.tetech.nl
please remove abc from the mail address