EMRFD Message Archive 4371

Message Date From Subject
4371 2010-02-24 14:18:05 Stephen Wandling DC Current Gain comparisons
I find myself launching into another learning experience, based on
G3XMB's XMB80-2 minimal transceiver (it makes the Pixie look pretty high
tech!). Roger used the venerable 2N3904 in his original and Alan Yates
used 2N2222s in his hopped up version.

Since I have a few different NPN transistors, I started reading
datasheets to get a notion of how to get the best h_FE on receive.
(This goal being based on my learning experience with the Flea or
"Pulga" rig)

This leads me to a question that most of you will probably find easy to

The 2N3904 datasheet gives five h_FE values for various I_C , with the
V_CE always at 1.0V. Now, I'm sure that in the circuit, the V_CE will
be different than 1.0V. So, I am not sure how I make use of this data,
on a practical level. Since and I_C of 10 Ma @ a V_CE of 1.0V seems
to have the highest h_FE , does that mean if my V_CE is 2.0 V, do I
assume that my h_FE would be the highest at 2 x 10 Ma or I_C of 20 Ma?

A corollary would be whether I can use your answer to the question
above, to compare datasheet data. E.g., the 2N2222 shows the h_FE with
the V_CE at 10.0 V.

Please remember that a lot of physics and formulas will be wasted on
me. Practical info with short words will be appreciated. ;-)