# Should we include Source and Load Impedance while calculating two port parameters?

While calculating the $$\Z\$$, or $$\Y\$$ or $$\h\$$ parameters of a two port network, should we include the source impedance and load impedance or not? In other words, for finding $$\Y_{11}\$$, we short the second port, my question is should we short the $$\V_2\$$ or replace it by its internal impedance? For example, in the following question,

the h parameters of a two port network are given below: $$\h_{11}=1\,;\, h_{12}=2\,;\, h_{21}=2\,; \,h_{22}=1\$$; O/p Power is $$\100\,W\$$; The network is excited by a voltage source, $$\V_s\$$ of internal resistance $$\2 \Omega\$$ Calculate $$\V_s\$$

Are the h-parameters given in the question, found out by including the $$\2\Omega\$$ internal impedance or without including it? Rather, how those specified parameters would've been found out initially? Does one two port network have only one fixed parameter (for Z, Y, etc)?

## 1 Answer

you shouldn't, the whole point of a two-port transformation is that you can use the simplified model and connect sources/loads as you see fit and see how it behaves regardless of source and load if you add the load to the parameters you would have to uncouple it from the equations every time you get a new load.

So I would leave out the impedance of the source and load out of any h/y/z or whatever parameters you are getting.

• So, the parameters depend only on the components inside the black Box? I mean, does one network have one fixed parameter(Z Y or whatever)? – Aravindh Vasu Aug 19 '19 at 3:26
• yes a network should have all its parameters depend only on internal values, Z or Y or whatever else are all equivalent so it should be the same for all. – Juan Aug 21 '19 at 4:29