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Calculating load impedance for coax circuit

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alqasim

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If I have the attached drawing setup what is the impedance seen from L side, knowing that the characteristic impedance for the coax is 50 Ω & the characteristic impedance for the loads are 50 Ω .

Is this information enough , Is there any simulation tool for coax circuits .
 

FvM

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Re: load impedance

You have a strong impedance mismatch and multiple reflections travelling between the T-connectors. The Circuit may be inappropriate for many applications.

Analysis is possible with general simulators as SPICE for frequency and time domain or with Smith Chart tools for frequency domain.

P.S.: The impedance is frequency dependant. The analysis must know all cable length between the T-connectors and to the L port.
 

alqasim

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Re: load impedance

Mr. FvM or anyone

would you please suggest some tools and simulators that i can use for this circuit other than SPICE.

Best regards,
 

radiohead

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biff44

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load impedance

If you are very low in frequency, and the coaxial lines are very short, the impedance is simply 10 ohms. If the lines get to be a significant fraction of a wavelength in length, then you have a complex impedance (resistive AND reactive parts) that has to be calculated using some complicated formulas.
 

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Re: load impedance

Best way to analyze this is in the freq. domain. Anyhow it looks like some sort of -badly designed- filter: the stubs behave like resonators and the interconnecting transmission lines like immittance inverters
. There are effectively no stubs (assuming a 50 ohm characteristic line impedance).

As a first analysis step, the circuit can be simplified for the load impedance calculation. All line with 50 ohms termination can be replaced by 50 ohms without a line. Thus, you have the horizontal interconnection with several mismatching nodes remaining for analysis.

you have a complex impedance (resistive AND reactive parts) that has to be calculated using some complicated formulas.
I don't think it's complicated. It's just a parallel circuit and rotation of complex impedances. It can be easily achieved in a smith chart or by pocket calculator supporting complex numbers.
 

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