I am trying to figure out how to calculate the input and output impedance for transistors. (Kind of an important detail when you are designing radio gear.)

The link below has some interesting examples. I grabbed some screen captures of them
in case they eventually fade away on the internet like so many good things do.

http://hyperphysics.phy-astr.gsu.edu/Hbase/Electronic/tranimped.html

The challenge that I have with these examples are that they appear to be DC values.
I live in an RF world which means we are talking about AC or even more complex is
DC & AC at the same time.

------

Here is another link that I like:

http://www.geofex.com/article_folders/impednc.htm

I have seen/read other examples like this where you roll up the values and get to
an approximate value.

This still bothers me. Why is it so hard to figure it out? We should be
able to calculate it and measure it. This feels kind of elusive and black boxish.
....arghhh.