On Sun, Jul 17, 2022 at 01:17 PM, <cariboome@...> wrote:
My question is: for some tuning, I often show a very low SWR (<1:1.05) with a
logmag reading of -15 or thereabouts, and another tune showing about the same
SWR but a logmag of -40, -50 or even -90 dB. The logmag trace sometimes
appearing as a very steep and deep notch, often at or in the SWR trace and
other times just a shallow dip. The Smith typically shows a fairly consistent
50 ohms plus or minus 1 or 2 at tuned resonance. Is this a representation of
reflected loss and VSWR being shown real time side by side? Is it better to
have a logmag reading of -90 dB let's say, as well as a very low SWR -- vs
very low SWR and a "higher" logmag of -20dB for instance?
Yes side-by-side as you put it.. The NanoVNA is calculating all the parameters (SWR, Return Loss (logmag format) and impedance (R, X) from the same scanned measurements. If your return loss is 14 dB you have a VSWR of about 1.5 which is fine for most purposes. If your SWR is higher than this modern solid state transmitters tend to cut back on their power output. A VSWR of 1.1 is a RL of 26 dB and that is excellent. Here is a link to a table of VSWR vs Return Loss. It also shows the reflected and through power. You should also be aware that Return Loss is a positive number but many publications use a negative sign which is not correct but done anyway. Yes confusing but the way it is...
Roger
Roger Need