Roy,

many thanks for taking the time to compose such a detailed reply.

I continued to experiment and make some more measurements, but I got
sidetracked into finally constructing a simple SSB receiver. I then got side
tracked into trying to figure out why the radio doesn't work very well. Even
the damn 2N3819 FET oscillator didn't work! I even tried different FETs. That
was fixed by adding extra source resistance.

The following table may not look right as it appears to have tabs in it.

vga in V
idd in mA
gm in ms
Rs in ohm
Rdrain
0.0 13.2 n/a 0.0 n/a
-0.2 12.1 5.1 17.6 196.35
-0.5 10.5 4.8 51.3 207.54
-0.7 9.6 4.4 77.0 227.01
-1.2 7.8 4.3 149.7 231.31
-1.5 6.4 4.2 227.1 240.46
-1.8 5.1 3.8 348.9 260.87
-2.1 4.1 3.5 498.8 284.05 - operating point
-2.5 2.6 3.2 984.4 312.25
-2.9 1.6 2.5 1781.3 398.94
-3.3 0.7 1.8 4808.8 541.10
-3.6 0.1 n/a 26000.0 n/a

I'd never heard of the effect of "effective drain resistance". I can't recall
seeing it explained in any of the texts which I have read. Mind you the PW
article suggested that the graph of Id vs Vgs was a straight line for smaller
values of Vgs! I re-calculated Rd using this extra value but I just got a less
than unity amplifier.

It seems to me and you seem to back this up the a FET buffer whilst a useful
impedance converter also distorts the signal due to the x squared function.
This makes it good for mixers though. I do often see FETs used as buffers for
VFOs in simple rx designs.

Anyway I'll do some more experimenting until I get theory and practice to match.

BTW I have already played with Spice, using it to plot various curves (Vd vs
Id for various Vgs, and Id vs Vgs). I have also simulated FET amplifiers and
buffers. Now I need to change the 2N3819 model to match the "slope" of my FET
and see what the simulator gives.

regards...

--Gary