Thank you :-) It's a time thing.. I work in the energy industry in Alberta and am away working in camps most of the time. Sometimes I wish I was retired already so that I could spend a lot more time on my hobbies.. haha!
👍Thanks for posting. 😄 This caught me out as well. I had never used a VNA before and I was thinking that the displayed phase angle didn't match what I expected for the circuit under test. Doh! After watching, I remembered that formula from the dim and distant past of transmission line theory.
Thanks man. I have a question if you would be so kind as to answer it. for example, S11 for a 50 ohm cable without an antenna and without a load at the end, the S11 read -2 dB 120°. Does this mean that the cable : do a phase delay of 60° and -1 dB attenuation ( " -1 = -2dB/2 ") or do a phase delay of 60° and -5 dB attenuation (-5 = -2 -3dB ) or do a phase delay of 120° and -1 dB attenuation ( " -1 = -2dB/2 ") or do a phase delay of 120° and -5 dB attenuation ( " -5 = -2 -3dB ") or do a phase delay of 120° and -2 dB attenuation . Will the phase and attenuation measurement differ when using S21, and how much will it differ? Which is more accurate in measuring phase and attenuation, S11 or S21? Thank you
The math shows why. The phase angle of the reflection coefficient is the difference in phase between the incident and reflected wave that the nanoVNA sees at the plane of reference where it has been calibrated. The phase angle of the circuit under test is the relationship between the voltage vs current in that circuit. As demonstrated, the phase of the voltage vs current in the circuit can be calculated from the phase of the reflection coefficient (the phase angle displayed by the nanoVNA). The phase of the voltage vs current in the circuit does effect the phase of the reflection coefficient so they are related, but they are not the same thing.
@@ve6wo I don't think they're related directly at all. The phase angle that is measured in the reflection coming back to the vna has to do with the delay of the incident wave and the reflected wave at the reference plane. You could change that angle simply by changing the length of the cable past the reference plane slightly, without changing the component values at all. I guess what it comes down to is talking about "complex impedance" of just the components is really an oversimplification, and ignoring the whole system (not taking into account any transmission line effects, which at low frequencies and "short" cables are negligible anyway), and what the VNA is measuring is the whole system together past the reference plane, including the transmission line.
@@gorak9000 your argument is valid. Consider this though, if you are measuring a reactive circuit or device and the reactance in that circuit or device changes, it will cause a change in the reflection coefficient, and the relationship is clear if one takes a look at the math :-)
The reflection coefficient measured by the VNA and the reactive behaviour of the device under test are unequivocally married. A change in the device under test will without doubt cause a change in the reflection coefficient, and from this information one can accurately ascertain the properties of the device under test so as to be able to firmly state the DUT’s complex impedance. This allows one to quite accurately characterize the behaviour of the device under test. One example of this is using the nanoVNA to determine the values of capacitors or inductors.
@@gorak9000 regarding measuring the whole system together past the reference plane, this is correct. That is why it is important to calibrate correctly and to use a suitable test apparatus for the frequencies and devices that are to be tested and/or characterized. We are not really ignoring the whole system, rather, we are intentionally arranging things so that we can ascertain the desired information about the DUT while controlling or minimizing those aspects of the system that we are not interested in knowing about. This is why I measure the nominal values of reactive components using low frequencies, to control those aspects of the ‘whole system’ that I am not interested in knowing about in the context of measuring capacitors or inductors.
We hope for more video. The content is missed. Just my 2cents.
Subbed, thumbs, shared on my social.
Thank you :-) It's a time thing.. I work in the energy industry in Alberta and am away working in camps most of the time. Sometimes I wish I was retired already so that I could spend a lot more time on my hobbies.. haha!
👍Thanks for posting. 😄 This caught me out as well. I had never used a VNA before and I was thinking that the displayed phase angle didn't match what I expected for the circuit under test. Doh! After watching, I remembered that formula from the dim and distant past of transmission line theory.
Nice presentation. Thanks.
Thanks man. I have a question if you would be so kind as to answer it. for example, S11 for a 50 ohm cable without an antenna and without a load at the end, the S11 read -2 dB 120°. Does this mean that the cable :
do a phase delay of 60° and -1 dB attenuation ( " -1 = -2dB/2 ")
or
do a phase delay of 60° and -5 dB attenuation (-5 = -2 -3dB )
or
do a phase delay of 120° and -1 dB attenuation ( " -1 = -2dB/2 ")
or
do a phase delay of 120° and -5 dB attenuation ( " -5 = -2 -3dB ")
or
do a phase delay of 120° and -2 dB attenuation .
Will the phase and attenuation measurement differ when using S21, and how much will it differ? Which is more accurate in measuring phase and attenuation, S11 or S21?
Thank you
Fantastic, thank you :)
You demonstrated the fact several ways, but i still don't know Why it is so ?
The math shows why. The phase angle of the reflection coefficient is the difference in phase between the incident and reflected wave that the nanoVNA sees at the plane of reference where it has been calibrated. The phase angle of the circuit under test is the relationship between the voltage vs current in that circuit. As demonstrated, the phase of the voltage vs current in the circuit can be calculated from the phase of the reflection coefficient (the phase angle displayed by the nanoVNA). The phase of the voltage vs current in the circuit does effect the phase of the reflection coefficient so they are related, but they are not the same thing.
@@ve6wo I don't think they're related directly at all. The phase angle that is measured in the reflection coming back to the vna has to do with the delay of the incident wave and the reflected wave at the reference plane. You could change that angle simply by changing the length of the cable past the reference plane slightly, without changing the component values at all. I guess what it comes down to is talking about "complex impedance" of just the components is really an oversimplification, and ignoring the whole system (not taking into account any transmission line effects, which at low frequencies and "short" cables are negligible anyway), and what the VNA is measuring is the whole system together past the reference plane, including the transmission line.
@@gorak9000 your argument is valid.
Consider this though, if you are measuring a reactive circuit or device and the reactance in that circuit or device changes, it will cause a change in the reflection coefficient, and the relationship is clear if one takes a look at the math :-)
The reflection coefficient measured by the VNA and the reactive behaviour of the device under test are unequivocally married. A change in the device under test will without doubt cause a change in the reflection coefficient, and from this information one can accurately ascertain the properties of the device under test so as to be able to firmly state the DUT’s complex impedance. This allows one to quite accurately characterize the behaviour of the device under test. One example of this is using the nanoVNA to determine the values of capacitors or inductors.
@@gorak9000 regarding measuring the whole system together past the reference plane, this is correct. That is why it is important to calibrate correctly and to use a suitable test apparatus for the frequencies and devices that are to be tested and/or characterized. We are not really ignoring the whole system, rather, we are intentionally arranging things so that we can ascertain the desired information about the DUT while controlling or minimizing those aspects of the system that we are not interested in knowing about. This is why I measure the nominal values of reactive components using low frequencies, to control those aspects of the ‘whole system’ that I am not interested in knowing about in the context of measuring capacitors or inductors.
Cool.
E.T.
Oh no! I’ve been discovered!
Hahaha!
Yeah, this is me geeking out, but I guess that’s not much of a surprise, eh!
The hobby keeps my brain working :-)
@@ve6wo yeah great video Gregg! I've been subscribed for a few months now.
@@Sethz71 Thanks man! So when r u getting your license so we can chat on 80 meters?
Sorry u are talking to your self!!!!!!
U dont know how to explain as a profetional !!!
@@israelhershkovits5675 Well, make a video and explain it properly then. I would be happy to learn :-)