Typically about 11pF tip capacitance...the "ground lead" introduces an inductance, which results in resonance at 100-125 MHz. I came up with simple method to calculate the capacitance, by putting a fast rising edge into a small inductor, and measuring the ringing frequency... You can do a math calculation, or simply add a 10-20 pF cap in parallel with the tip, and check the difference in the ringing frequency. Probing is really the number one technique that should be part of any oscilloscope training for new employees.(Former AE atvTek, Agilent, R&S)
That is a clever way to identify inductance. I think you can do similar to figure out inductor self resonance too but not sure. This video came about from belief, from my colleagues, that scope probes are Mega Ohms in impedance. Maybe its Mega Ohms at audio but not at RF. Probe and cable capacitance forms a low pass filter. I pretty sure Dave Jones (EEVBlog) and others (Al Wolke W2AEW) talks about this. I think one of them even developed an LTSpice model. Thanks for the feedback its something I need to keep in my back pocket.
Very interesting. A technique I find useful is to make provision on the board being designed for miniature 50 Ohm RF connectors at all the likely test points, I've then got an adaptor that fits into them that fits into the mini BNC connector that the end of the probe fits round. One advantage of doing this is that you reduce the pressure pickup in the ground lead.
@@DaveVE3OOI The connectors I used were Molex 73415-2121 (RS part: 904-8228) for the board side and Molex 73415-1472 (RS part: 265-9425) for the probe adaptor side. They are 50 Ohm and have a nice push-click mechanism. As for the footprint, I had to draw it myself, but that's quite easy in KiCAD these days, especially if you download the 3D model of the connector and test you've got it right. The socket for my LeCroy scope probe has part number PK5-2.5MM-113, but I think the dimensions for that aren't likely to match all probes, just the LeCroy style ones.
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Typically about 11pF tip capacitance...the "ground lead" introduces an inductance, which results in resonance at 100-125 MHz.
I came up with simple method to calculate the capacitance, by putting a fast rising edge into a small inductor, and measuring the ringing frequency... You can do a math calculation, or simply add a 10-20 pF cap in parallel with the tip, and check the difference in the ringing frequency.
Probing is really the number one technique that should be part of any oscilloscope training for new employees.(Former AE atvTek, Agilent, R&S)
That is a clever way to identify inductance. I think you can do similar to figure out inductor self resonance too but not sure. This video came about from belief, from my colleagues, that scope probes are Mega Ohms in impedance. Maybe its Mega Ohms at audio but not at RF. Probe and cable capacitance forms a low pass filter. I pretty sure Dave Jones (EEVBlog) and others (Al Wolke W2AEW) talks about this. I think one of them even developed an LTSpice model. Thanks for the feedback its something I need to keep in my back pocket.
Very interesting. A technique I find useful is to make provision on the board being designed for miniature 50 Ohm RF connectors at all the likely test points, I've then got an adaptor that fits into them that fits into the mini BNC connector that the end of the probe fits round. One advantage of doing this is that you reduce the pressure pickup in the ground lead.
I have used those. I could not find a good footprint. The one I used lifted the copper. Which do you use?
@@DaveVE3OOI The connectors I used were Molex 73415-2121 (RS part: 904-8228) for the board side and Molex 73415-1472 (RS part: 265-9425) for the probe adaptor side. They are 50 Ohm and have a nice push-click mechanism. As for the footprint, I had to draw it myself, but that's quite easy in KiCAD these days, especially if you download the 3D model of the connector and test you've got it right. The socket for my LeCroy scope probe has part number PK5-2.5MM-113, but I think the dimensions for that aren't likely to match all probes, just the LeCroy style ones.
@@AllTheFasteners Ok. I was referring to the U.FL SMT part. This is a through hole which has much more mechanical strength. Thanks.