Computing The Loop Terminating Resistance Rt

** Circuit Description **
* input source set to zero for output impedance calculation
Vs 11 0 DC 0 AC 0
Rs 11 10 10k
* short-circuit output port
Vout 0 9 0
* power supply
Vcc 1 0 DC +12V
* amplifier circuit
* 1st stage
Rc1 1 2 10k
Q1 2 3 4 Q2N3904
Re1 4 0 870
Ce1 4 0 1GF
Rb1 1 3 100k
Rb2 3 0 15k
* 2nd stage
Rc2 1 5 8k
Q2 5 21 6 Q2N3904
* decoupling capacitors
Cc1 10 3 1GF
Cc2 5 8 1GF
* load
Rl 8 9 1k
* feedback circuit
Re2 6 0 3.4k
Rf 3 7 10k
Cf 6 7 1GF
* inject signal into feedback loop without disturbing DC bias
Lt 2 21 1GH
Cti 21 22 1GF
Vt 22 0 AC 1V
* transistor model statement for 2N3904
.model Q2N3904  NPN (Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259
+                    Ise=6.734f Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2 Isc=0 Ikr=0 Rc=1
+                    Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 Vje=.75
+                    Tr=239.5n Tf=301.2p Itf=.4 Vtf=4 Xtf=2 Rb=10)
** Analysis Requests **
.AC LIN 1 1Hz 1Hz
** Output Requests **
* print resistance seen by Vt: Rt=V(22)/I(Vt)
.PRINT AC Vm(22) Vp(22) Im(Vt) Ip(Vt)
.end