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SWR, return loss results depend upon the measurement reference - they are relative measurements.Īt this time, nanoVNA seems to have 'baked in' the idea that 50 ohms is some kind of chart center. But the measured values in each case will still be correct. On a 50 ohm chart, a 75 ohm resistance will show up as a point to the right of center, on a 75 ohm chart a 50 ohm load will be to the left of center. Of course, measuring 50 ohms in a 75 ohm environment or vice versa will both show a mismatch. Thus apart from imperfect fixture/connector environment (non-TEM, imperfect equivalence between calibration devices and measurement environment) the Smith Chart continues to give the correct answer.Ī perfect 75 ohm match on a Smith Chart referenced to 75 ohms will reveal 1:1 SWR in the same way that a perfect 50 ohm match on a 50 ohm referenced chart will.
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The center of a Smith Chart is not 50 ohms - it's the reference load. In an ideal (TEM) environment and connector type/fixture, the center of the chart will be the reference impedance you used, whatever that may be.
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" If you connect the 50Ω std., it now appears at 50Ωs on a chart normalized for 75Ω," > tail off below 470, with best rejection 420 -430 MHz.probably only need > I need to pass above 470MHz, could live with 1 or 2dB through loss. > I am building a 75 ohm TVI - DMR filter using multiple stubs out of 75 ohm > Is it valid to simply do the calibrate procedure, but using R75 feeders On Thu, at 9:24 PM PETER LAWRENCE via groups.io wrote: With the outliers when they occur during my design and home brewing needs. I'm happy to have a good instrument that is devoted to 50-ohms. The trade-offs (based on Bell Lab studies in the mid to late 40's for High Pulsed Power Research applications: 0.5 to 5-ohms High Power Laser feeds: 2-ohms (slab line) If there were VNAs for every requirement:Ībout everyone in RF communications: 50-ohms Measure the Minicircuits units for the same porpose. That way, you know precisely what you are dealing with. Or, since you have a VNA, design and measure your