Two-ports

Finding the parameters

Find equivalent → Two-port parameters, two nodes, and a kind:

ra,1,2,10
rb,2,0,20
rc,2,3,30

A T network. Ports at 1 and 3:

10 + 20 and 30 + 20 on the diagonal, the shared 20 off it. z12 = z21 because the network is reciprocal — passive and source-free. A network with a dependent source in it will not be, and that is a result rather than a mistake.

Run it again with y and you get the inverse matrix, as you should.

A two-port as an element

The same six letters are element types. Give the block its four parameters in brackets and it behaves as that two-port:

e,1,0,10
r1,1,a,50
z1,a,b,[100,10,20,50]
rl,b,0,1'k

The order is [p11,p12,p21,p22]. Leave the brackets off and the parameters become symbols — zp11, zp12 and so on — which is how you solve for the block a circuit would need.

A two-port reports a current at each port, named for the element and then the node — a block z1 with ports at a and b reports iz1a and iz1b. With four terminals named, it reports four.

Four terminals

z1,[tl,bl],[tr,br],[…] when neither port sits on ground — the same form as the transformer in Mutual inductance and transformers. A port whose far side floats gets its own reference automatically, and Symbulator says so in the notes rather than refusing.

The gain mini-tool

gain takes a two-port and a load and returns what a cascade designer actually wants:

It is a mini-tool, so it takes the four parameters and the load as values you type rather than needing a circuit.