During the presentation of the NanoVNA last night, the group noticed that the VSWR plots of the 6M antennas didn't look right (i.e. too good) and we speculated that I might have generated the graphs without calibrating the unit generating the plots.? So today I reran the VSWR plots with an un-calibrated unit, two calibrated units and then tested the antenna with an old MFJ 259B.? The results (graphical comparison at the bottom of the spreadsheet).? The uncalibrated NanoVNA gave results that were similar to what we saw on the presentation slides (too good).? After calibrations (unit 1 with a 10 sweep average, unit 2 with 1 sweep), the VSWR curve looks like we would expect for the Omni Angle outside of the 6M band.? The two NanoVNAs were very close in their measurements, the minor? differences most likely being due to the single sweep results versus the average of 10 sweeps.? The MFJ 259B is directionally consistent with the NanoVNAs but tends to understate the VSWR as frequencies move away from resonance; or the MFJ is right and the 2 NanoVNAs are wrong.
Anyway, if you are interested have a look at the data and the graph.? Please let the group know if you have any observations or comments.
Harry W
KF2TV
