Measuring the Input Impedance of a Product, Circuit or System (070b)

There are two kinds of situations where you might want to measure the input impedance of a product, system or circuit: 1. At a Low frequency like an audio amplifier where there is no real concern about the complex aspects of impedance. 2. At Higher frequencies like a receiver pre-amp where we are very much interested in the complex impedance. I covered the first of these in the last video. If you missed that one, here is the LINK to it: https://youtu.be/JCcHrXeIaYQ In THIS video I will be measuring the input impedance of a VHF preamp that is part of my little 2 meter amplifier. I will see if we can do this with the nanoVNA. Regardless of what VNA I use to make the measurement, the principles remain the same as to how to go about it. These principles can be applied to other amplifier where the nanoVNA can be used, so stay tuned regardless. There are some rather surprising results to our efforts. One of these is the actual SWR which is represented by the measured input impedance at 144 MHz. I kept puzzling at this. I verified it by at least two on-line calculators (Impedance-to-SWR calculators), by my Excel spreadsheet that I developed and by my manual calculation. They all came up with the same numbers! ======================================= Time Markers for Your Convenience ---------------------------- 00:05 Introductory Comments 01:08 Planning Our Measurement 01:13 Concern #1: Input Requirements 03:41 Can the nanoVNA do this? 03:50 nanoVNA Setup 04:41 nanoVNA Results 06:30 Can the Tektronix VNA do this? 06:59 Tektronix VNA Performance 07:29 Concern #2: Output Loading 08:00 SETUP 08:00 Connections 09:37 Tektronix VNA Setup 09:39 Settings 10:33 Calibration (VERY QUICKLY!) 11:16 Adding the Port Extension 12:30 Making the Measurement 12:33 Getting the Amplifier ready 13:05 Measurement Results 14:35 Conclusions and Debriefing 15:25 Toodle-Oots