I now used the H-field probe as with the nanoVNA to measure the H-Field with the scope.
See setup in picture.
Calibration was done with small single loop litz directly on the FG, see screenshot 1
Measurement was done with a 50MHz sweep, see screenshot 2.
We see a peak at 17Mhz and 32MHz.
The hookups are OK, but there is some nasty aliasing of the RF signal with the scope's sample rate, which makes it difficult to process the csv files numerically. Please test for the aliasing first with the FG connected directly to the scope. The signal should not disappear like the attached one at 3.10E-02s due to aliasing. 10s sweep time is fine, but please repeat it with an integration time set below the half of scope's sampling rate... that setting might be near the "bandwidth limiting" settings or sample averaging in acquisition menu. For example my scope has this RMS mode in which up to 16M samples can be squared and added up inside the FPGA on the fly and then only their average (sqr actually) is written to scope's memory. I have seen other scopes having a similar acquisition mode where the absolute values of the samples are averaged arithmetically instead, and then only their average is written into scope's memory*. If your scope has a similar mode - please use it. With such memory saving acquisition modes, e.g. 10G samples do not need to be written into scope's memory when the scope samples at e.g. 1Gsps for 10s and the high (1GSps) sampling rate prevents aliasing of all signals below 500MHz. Also, some i-Probe amplifiers have an RMS mode and their output in this mode only needs to be low pass filtered at kHz frequencies to avoid aliasing. * In analog world this is equivalent to a high-frequency rectifier followed by an RC integrator.
« Last Edit: 2020-09-22, 01:47:06 by verpies »
|
Author
Topic: Smudge proposed NMR experiment replication. (Read 126979 times)
