On Wed, 17 Nov 2010 14:09:11 -0600, "amdx" wrote:

At low signal levels the RF input
resistance and audio output resistance of a detector diode are equal to
25,700,000*n/Is Ohms (current in nA).

25 million WHAT?

Ok One more, with a little help I figured it out.
It has to to with the Thermal Voltage of the diode.
Vt=KT/q
with k=1.38E-23 and q=1.6E-19. T is absolute temperature in degrees Kelvin,
k is Boltzmann's constant and q is the charge of an electron. VT is close
to 0.025 volts at 20 degrees Celsius.

With a slightly increased temperature the .025 is raised to .0257,
and .0257 / 1 nanoamp =25,700,000
Thanks, MikeK


Hi Mike,

So, for the complete expression:
25,700,000*n/Is Ohms (current in nA).
you take the same current and divide it out to yield
0.025*n
where n, as I observe (but fail to see the significance of) is a
multiplier of nearly 1.

Putting this back into the complete expression in the complete
statement:
At low signal levels the RF input
resistance and audio output resistance of a detector diode are equal to
0.025 Ohms (current in nA).
or with temperature change:
0.0257 Ohms (current in nA).

Sounds fairly trivial when we are talking about tenths of milliOhms
per degree facing into source Z of a million times that, and feeding a
load resistance that is at least a thousand times larger.

This temperature dependency, too, is something I worked with 30 odd
years ago. The temperature characteristic has been around as long as
the solid state diode. I used it specifically for measuring
temperature, as does every inexpensive electronic thermometer. My
design used a constant current LED (to indicate a complete circuit)
and a common diode in series, with that diode placed at the point of
interest where temperature was a production flow variable. The
voltage across that diode, minus an offset for Kelvin, was a linear
indication of temperature, usually accurate to within 1 degree C, if
not slightly better. The coefficient is roughly 2mV/degree C.

The one oddity I find with the original material you cite is that it
specifies Is which is a reverse current, and the temperature
dependency is for forward voltage characteristic curve.

Such things make me question the authenticity of these sources.

73's
Richard Clark, KB7QHC