On 4/2/2015 12:36 PM, amdx wrote:
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

That voltage is going to be pretty small. Unless your signal is strong
and close, it will be low uVolts.

--

Rick