Complex src impedance

What does it mean when a source/generator is said to have a complex impedance?
What kind of sources have complex impedances?

M

I think this is the case when you are considering frequencies lower or larger than the center frequency of the source. i.e. frequencies around the resonance

Every kind of source in practical life. (Is more or less only signal generators and measure instruments port have 'pure' resistive signal source on wide frequency range - and pay very much for this...)

ie source similar to load have reactive component of any kind parallell and/or in serie with exist part of real resistance in port and togetheter give complex impedance. Also using real source @ 50 Ohm, but using coax cable @ 110 Ohm to load, you make complex source depend of length of cable (in part of wave lengt of used frequency) .

(if you are familiar with Smith chart, every place outside real axis in chart is a complex impedances if you measure S11 on source port)

Cable transporting low frequency (< 100 KHz) on long distance is a typical complex 'source' - here is very capacitive.

Mostly RF-power amplifier and transistors have not pure resistive impedances on input and output, and filters is very reactive outside passband and little lower in band etc.

Many crystal and SAW-filters needs using complex (capacitive most case) impedance from source and load on port to work correctly.

etc. etc.

---

Very big part of RF-design work is just handling and transforming of complex load and source between components and filters. And people not understud this - seems this work very 'magic'... and why calculators/programs/applications with complex support is so importent in this kind of work...

Complex sources are the ones with too many buttons and knobs.

biff44 its not "Complex Source", its "Complex Source Impedance"
Anyway, is there a way to determing the source impedance of a signal source?