Related only to the magnitude, and not the phase, remains unchanged - for a So whilst the impedance change, the SWR, which is The transmission line changes the impedance (both R and X) but does notĬhange its magnitude. Ohm coax) alter the impedance (at your radio) but does NOT change the SWR There are multiple ways of basically writing the same information.Īnd finally, why does changing the LENGTH of the feed line (again, say 50 Sometimes the reflection coefficient is expressed in dB too. When on a transmission line, it can be expressed as a reflectionĬoefficient. It has aĪnd a phase angle of arctan(50/50() = 45 deg However, it can be expressed in different ways. I don't think it would achieveĪnything useful to give you those equations. The impedance can be expressed as a reflection coefficient, andįrom the magnitude of the reflection coefficient, which depends on the coax
Hence there is an infinite number of impedances that have the same Impedance is a vector quantity - it has magnitude and phase. * The imaginary part of the impedance is different. That alone means the impedances are not the same. * The real part of the impedance is different (one is 30 ohm, the other 40 Why is that?īecause there is an infinite number of different impedances that have the There are zillions of combinations of R,X that (with 50 ohm coax feed *They don't!* If R *or *X changes, the impedance changes. Was kind of a piece of magic for me as I thought about this Why do different values of R and X have the same impedance? That So on my PPT presentation, I added a few slides about Smith Charts and
#Vna smith chart pdf
Watch out - there is a short QUIZ at the end of this pdf file. With appreciation for all of the helpful comments from this IO group.
So for me, at least, the Nano VNA is a device that allows (almost requires) going over some fundamentals about antennas, impedance, R and X values, and matching. I find few hams at Zoom meetings can answer that concept in a sentence or two. Why is 40 + j30 ohms a different impedance from 30 + j40 ohms?Īnd finally, why does changing the LENGTH of the feed line (again, say 50 ohm coax) alter the impedance (at your radio) but does NOT change the SWR (at least not by much). There are zillions of combinations of R,X that (with 50 ohm coax feed line) can have the identical SWR. Why do different values of R and X have the same impedance? That was kind of a piece of magic for me as I thought about this. So on my PPT presentation, I added a few slides about Smith Charts and Antenna Impedance: I've been a licensed ham for over 60 years, but rarely if ever did I have to look at or discuss a Smith Chart of an Antenna.īut having a Nano VNA forced me to relearn about plotting R and X values on a Smith Chart. In my Zoom presentations on the Nano VNA as an antenna analyzer, I often get to the topic of looking at "Antenna Impedance" (Resistance and Reactance plots) on a Smith Chart.
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