Re: nanoVNA Maximum Impedance Measurement (Folded Dipole example)
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Greetings,
Using the "NanoVNA-Saver" PC app to control my mid quality nanoVNA I spent considerable time testing the high impedance measurement accuracy. I had previously made up a variety of loads using paralleled 0805 SMD resistors mounted on the back of BNC PCB through hole connectors. Thus with my loads I needed to use an SMA/BNC adapter which added a slight amount of shunt C which I subtracted out of the results. In a nutshell I found my nanoVNA is quite accurate, within about 2%, for loads up to 1K Ohm for 2M measurements. Thus I think if used properly your nanoVNA should work well for measuring a 300 Ohm load. You may find this thread of interest: /g/nanovna-users/message/2146?p=,,,20,0,0,0::relevance,,VA7TA,20,2,0,33508471 The folded dipole measurement case presents a balanced load the unbalanced input of the nanoVNA. This may upset the balance and introduce an error. You could consider making a 4:1 half wave coaxial balun (See Attached) that would provide you an unbalanced measurement point for the nanoVNA and would step the impedance down to the the 75 Ohm region. It would allow you to use a relatively long RG58 coaxial test lead that would facilitate making the measurement a wavelength or two away from the dipole to reduce any antenna coupling proximity effects. Prior to making the measurement you would need to extend the calibration reference to the antenna unbalanced balun interface end of the long test lead using the usual SOL calibration procedure. -- Enjoy! Tom VA7TA |
