Re: No audio driver
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I haven't had reason to play with diode RF probes. But here's a quote from http://www.tuberadioforum.com/t4138-simple-rf-probe-for-my-dmm suggesting they work well enough at far far lower RF voltages than you might think:
This one is a bit more sophisticated. It is still a passive probe, but can be calibrated in both output and linearity. Its minimum sensitivity is about 2.3 mVrms input, and in testing so far, has an essentially a flat response from high audio frequencies to about 30 MHz I have not gone beyond that, but it should be good to 100 MHz or so. The main difference with this RF probe is the fact that it is just about dead on 1:1 RMS input to DC output from 150 mV to past 15V. Again, it should continue to be linear, but I have not tested its voltage response beyond about 26 dB.
Most of the RF probe designs out there use the meter's internal resistance in series with a resistor in the RF probe to convert pk-to-pk into rms voltage. Careful with that if using an external meter, as they can have an order of magnitude difference in internal resistance.
Another point often not mentioned is that the probes use that series resistor in the probe plus any stray capacitance inside the meter to form a low pass filter, creating the DC voltage that gets measured.
On Sun, Apr 2, 2017 at 07:53 am, Jerry Gaffke wrote:
Actually, a germanium (and likely even schottky) diode probe can work down below 100mv if the current is kept low enough