Re: Measuring different results
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Btomek:
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I think you are saying "A moderate change in impedance (resistance + reactance) has little effect on thee SWR/reflection coefficient when the SWR is close to 1:1 but a large effect when the SWR is high to start with." Is that about right? I found this on Wikipedia: "SWR is usually measured using a dedicated instrument called an SWR meter. Since SWR is a measure of the load impedance relative to the characteristic impedance of the transmission line in use (which together determine the reflection coefficient...), a given SWR meter can interpret the impedance it sees in terms of SWR only if it has been designed for that particular characteristic impedance." Just as you stated. BTW, I seldom contribute to this forum but I read most of the posts and find the discussions quite educational. Thank you all! - David Ham KD6DWR/GMRS WQYV533 -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of btomek@... Sent: Sunday, October 10, 2021 7:15 AM To: [email protected] Subject: Re: [nanovna-users] Measuring different results The NanoVNA measuring bridge at the S11 connector is in equilibrium at a load of 50 Ohms, and works most accurately in this region. The further away from 50 Ohms the more error there is in the measurement per R and X. The NanoVNA measures the reflection coefficient, and for this 910+j1610 we have SWR=75.21, and for 1580+j1880 SWR = 76.36. This corresponds to a reflection coefficient of 0.9738 and 0.9741. As you can see, the difference is only 0.0003 of the reflection coefficient. For comparison, 46.5+j2.85 = SWR 1.098, 46.2+j2.48 = SWR 1.099. The corresponding reflection coefficients are 0.04671 and 0.04717, a difference of 0.00046. -- This email has been checked for viruses by AVG. |
David Reichard