# Matlab - Coax cable

Discussion in 'Programmer's Corner' started by stevenekp, Oct 19, 2007.

1. ### stevenekp Thread Starter New Member

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

2. ### recca02 Senior Member

Apr 2, 2007
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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.

3. ### stevenekp Thread Starter New Member

Oct 19, 2007
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However, it is matlab. I am thinking there is a mathematical representation?

4. ### recca02 Senior Member

Apr 2, 2007
1,211
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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.

5. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
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?

6. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
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

7. ### recca02 Senior Member

Apr 2, 2007
1,211
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i do not know abt mathematical function but there was one model of coax transmission IIRC. can that be converted to matlab function?

8. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
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

9. ### stevenekp Thread Starter New Member

Oct 19, 2007
3
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Thanks for your suggestions. will investigate and get back to you on this.