# Matlab - Coax cable

#### stevenekp

Joined Oct 19, 2007
3
New to matlab. How do I represent a 50 ohm, 1km coax cable in matlab?

#### recca02

Joined Apr 2, 2007
1,212
i have a little experience with simulink (and almost zero with matlab)
but in simulink there is a model for coax transmission line.
just search coax in simulink help.

#### stevenekp

Joined Oct 19, 2007
3

However, it is matlab. I am thinking there is a mathematical representation?

#### recca02

Joined Apr 2, 2007
1,212
this seems to be beyond me,
will it be possible for u to make a mathematical representation based on electrical model(schematic).
try this: http://en.wikipedia.org/wiki/Coaxial_Cable
hopefully that shud help.

#### Papabravo

Joined Feb 24, 2006
21,018

However, it is matlab. I am thinking there is a mathematical representation?
Gonzalez, G., Microwave Transistor Amplifiers, has a mathematical treatment of transmission lines that you might find helpful. The model is basically a sequence of series L's and shunt C's terminated in the characteristic impedance. In this case no signal power is reflected from the termination. For an open, or a short, or any other load besides the characteristic impedance some of the power will be reflected back towards the source. The reflection may be in phase or out of phase. Does this help?

#### Dave

Joined Nov 17, 2003
6,969
There isn't a standard co-axial function in Matlab or, as far as I remember, Simulink. Therefore you will need to look at a mathematical treatment of the cable. Further to PBs suggestion above you should look at the relevant section here in the e-book which deals with the theory from a 50-Ohm coax cable to a transmission line: http://www.allaboutcircuits.com/vol_2/chpt_14/index.html

In particular, look at the section on characteristic impedance: http://www.allaboutcircuits.com/vol_2/chpt_14/3.html

Dave

#### recca02

Joined Apr 2, 2007
1,212
i do not know abt mathematical function but there was one model of coax transmission IIRC. can that be converted to matlab function?

#### Dave

Joined Nov 17, 2003
6,969
i do not know abt mathematical function but there was one model of coax transmission IIRC. can that be converted to matlab function?
If there is a mathematical model of something, you should be able to represent it in Matlab without problem. The above e-books links give the basis of that model for coaxial cables in the form of TM lines.

Dave