Re-test of 6M Omni Angle

#23

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

6M Omni Angle Re-test.xlsx

#24

Harry W.,?

Nice to see that the observations made by the audience were indeed well founded. As we get more gadgets and apps, it's always good to question the results by asking, "does that make sense?"?

Imagine what could have happened if you tried to operate a radio in a portion where the swr was really not as good as originally thought.?

Thanks again on an excellent presentation.

Best Regards,

Harry R.

W2HRY

Show quoted text

On Fri, Feb 14, 2020, 1:16 PM <hwillia1@...> wrote:

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

#25

Thanks Harry R!? It also proves the point as we discussed that with these devices, calibration is a must, not a nice to have; the experiment makes that point nicely.? It also suggests that "single sweep" analytical results have inherent error compared with multiple/averaged results with "outliers" removed, which the Saver software allows. I have learned that periodic retesting of my antennas is necessary, where my latest review uncovered high SWR in my 2M/70cm halo; probably a bad connection....

I am in the process of using the NanoVNA to optimize my Palstar AT2K for the lower bands where minor changes in inductance or capacitance have large impacts on resonance.? I have been playing around with tuning my end-fed long wire antenna for 160M where it is easy to see how very minor adjustments to the tuner make big changes in the return loss or VSWR profile.? I'll send out a few examples down the road.

Harry W - KF2TV

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From: "Harry Ramos"
To: [email protected]
Cc:
Sent: Saturday February 15 2020 2:47:42PM
Subject: Re: [xarc] Re-test of 6M Omni Angle