"amdx" wrote in message
...
On 4/2/2015 9:23 AM, Jan Panteltje wrote:
On a sunny day (Thu, 02 Apr 2015 09:10:47 -0500) it happened amdx
wrote in :

I'm about to build this circuit to compare output from different
ferrite receive antennas. I will be using it with the the FET amplifier
referenced at the bottom of the page, so the input impedance is not a
concern. I'm mostly interested in the DC output to monitor signal
levels. AM band frequencies.

http://www.crystal-radio.eu/diodedet...dedetector.htm

Any fix for the sinewave distortion in the second and third scope
traces.
Mikek

If you really want to be linear for small voltages at ferrite rod
frequencies
then a small opamp diode detector would be a lot better.

http://en.wikipedia.org/wiki/Precision_rectifier



So, you think the distortion is caused by the diodes and some gain ahead
of them would solve that problem.
I don't know how important linearity really is, I just want a relative
comparison between antennas. However, if I build it better,
it may have more use in the future.
He says it listenable at 10mv, which seems high compared to the
sensitivity of a good AM radio.
I'll be measuring across a resonant ferrite rod, I don't know what a
minimum usable voltage would be. I'll go check.
Mikek


If you want more sensitivity, put some (tuned ?) gain in front of the
detector. Low noise amplifier is best for the first stage.