~ Transistor r_bb Calculated from data sheet figures ~

Boltzmann Constant — k	1.38062×10-23	J/K   [ Joules/Kelvin ]
Charge on a Single Electron — q	1.60218×10-19	C   [ Coulomb or Amperes/sec ]
Noise Voltage Referred to Input — en		nV/√Hz   from data sheet
Collector Current for en — IC		mA   from data sheet
Transistor d.c. current gain — β		hFE   from data sheet @ IC
Device Temperature — T		˚C  =  ˚K
Measurement Noise Bandwidth — Bn		Hz — Is not the –3dB BW as Here
Calculated results using the Variables entered above
Emitter Internal Resistance — re		Ω = VT/IC   VT= kT/q =  mV
Noise due to IC — VNIC		nVrms = √2 q IC Bn
Calculated Base Resistance — rbb		Ω     and the -ve answer    Ω?

The calculated rbb result must be positive [ and Green ] and the –ve result negative for the answer to be correct ~ If the noise referred to the input is not measured in /√Hz but in a given bandwidth then B_n should be changed to match but e_n must be nV ~ If an output is NaN [ Not a Number ] check inputs are all numeric and e_n not too low or B_n too high

Some transistor parameter testers of the past used to derive data sheet Noise Voltage Referred to Input or rbb directly had resistance in the Base–Emitter path that made rbb effectively up–to 10Ω or more higher ~ The best way to measure rbb is to have specific test jigs for each transistor type that ensure the B–E path is as close to zero  as possible

" Do you work it out one by one ~ Or played in combination "