In the twisted pair cable impedance calculator there is a value "substrate dielectric" - an integer value.
What does this number represent, please?

https://www.allaboutcircuits.com/tools/twisted-pair-impedance-calculator/

 

Hey, Albert—

That would be the relative permittivity of the material used as the wire’s insulation. It’s not at all clear from the label on the filed but in the explanation of the math further down the page, the term \(e_r\) which clarifies they are looking for relative permitivity.

Relative permittivity (\( e_r \)) is dimensionless. It is the ratio of the permittivity of the dielectric material (\( e \)) to the permittivity of free space (\( \epsilon_0 \)):
\[\epsilon_r = \frac{e}{\epsilon_0}\]
Where:
\( e \) is the permittivity of the material.
\( \epsilon_0 \) is the permittivity of free space (approximately \( \mathsf{8.854 \times 10^{-12}\space F/m}\)).

Permittivity is the measure of the ability for a non-conducting material to contain charge which of course would affect capacitance and so impedance.

Hope that helps.

 

Hey, Albert—

That would be the relative permittivity of the material used as the wire’s insulation. It’s not at all clear from the label on the filed but in the explanation of the math further down the page, the term \(e_r\) which clarifies they are looking for relative permitivity.

Relative permittivity is dimensionless,

Relative permittivity (\( e_r \)) is dimensionless. It is the ratio of the permittivity of the dielectric material (\( e \)) to the permittivity of free space (\( \epsilon_0 \)):
\[\epsilon_r = \frac{e}{\epsilon_0}\]
Where:
\( e \) is the permittivity of the material.
\( \epsilon_0 \) is the permittivity of free space (approximately \( \mathsf{8.854 \times 10^{-12}\space F/m}\)).

Permittivity is the measure of the ability for a non-conducting material to contain charge which of course would affect capacitance and so impedance.

Hope that helps.

Hi,

They also give numbers for the dielectric. Wouldn't it be better to provide a selection for different materials commonly used or something?

 

Hi,

They also give numbers for the dielectric. Wouldn't it be better to provide a selection for different materials commonly used or something?

I think it would probably be best to provide the option for entering a value or selecting materials from a dropdown.

 

Oh, and @AlbertHall, the value for that field is not an integer it accepts floating point numbers. It would have to since it is a ratio and is in no way constrained to integers.

 

I think it would probably be best to provide the option for entering a value or selecting materials from a dropdown.

Yes it would be nice to have both. Would be very convenient with an added list of materials to select from.

 

Oh, and @AlbertHall, the value for that field is not an integer it accepts floating point numbers. It would have to since it is a ratio and is in no way constrained to integers.

OK, thanks, I get it. That box has up/down arrows which inc/dec an integral value.

 

Took an eye on that resource and just frozen - how it can be that Zo is not dependant on how much wounds per inch are made? Sure the twist is largely cancelled by the interference induced oppositely in the second half. Thus if to broke 5 to 6 twists per inch then radiation outflux may increase hardly, respective active resistance, and Zo must fall down.