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Plotting QMX LPF's with a nanoVNA is not something I've done but:
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With the rig off, there should be zero volts across the 1n4007 diodes, isolating the LPF and making it possible to simply connect it up to the VNA for a two port test of the LPF.? The nanoVNA drives the device under test with a very low level signal, not big enough for the 1n4007's to conduct.? The 47uH inductor blocks any RF, so it will not be seen by the nanoVNA.? I would expect a somewhat similar plot from the nanoVNA as the QMX diagnostics give, but 1n4007 capacitance with the rig off, and the effects of other components upstream and downstream from the filter when the rig is transmitting will make the nanoVNA plot somewhat different.
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Hopefully somebody who has done this will report their technique and results.
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Doubt you need to pull that 470k resistor (or the 1n4007's), but two pin surface mount parts are easy enough to pluck off using two soldering irons.? For 3 pin SOT23's, you can first lift the one lead and tip the part up a bit, then go after the other two.? Clipping SOT23 parts (and bigger) with very small fine tipped diagonal cutters or an Xacto knife can work with the right technique, but you risk mechanically ripping the pads off the board if done wrong.? These boards are factory stuffed with no-lead solder, so you need some really hot soldering irons to melt it.
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Jerry, KE7ER
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On Fri, Dec 6, 2024 at 09:39 AM, Cal (AD8Q) wrote:
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