Calculating load impedance for coax circuit

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alqasim

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

Super Moderator
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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

Mr. FvM or anyone

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

Best regards,

biff44

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.

FvM

Super Moderator
Staff member

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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