Measuring SWR on an Ed Fong J-Pole with a NanoVNA

I have an Ed Fong roll up J-Pole antenna for use with 2M/70cm HTs. It's currently hanging from a thumb tack pushed into the wall of my shack up near the ceiling. I thought it would be interesting to measure the SWR (Standing Wave Ratio) on it for 144 Mhz through 446 Mhz, using a NanoVNA. 

After getting the reading I uploaded the picture to Google Gemini, ChatGPT, and Grok for analysis. Here's what Grok had to say:

This is a classic NanoVNA SWR (Standing Wave Ratio) plot of an Ed Fong-style dual-band J-pole antenna (2 m / 70 cm).

What the Graph Shows

• X-axis (horizontal): Frequency sweep from 144.000 MHz (START) to 460.000 MHz (STOP).
  This covers the entire 2-meter band (144–148 MHz) and most of the 70 cm band (430–450 MHz), plus the frequencies in between.
• Y-axis (vertical): SWR, scaled from 1.00 (bottom of the screen) to 1.75 (top of the screen).
  The labels at the top (“CH0 SWR 1.00/ 1.75”) confirm this narrow scale, which zooms in on the good-performance region.
• Blue trace: Measured SWR at each frequency (derived from the reflection measurement on CH0 / S11).

Key rule for reading SWR plots on a NanoVNA:
Lower on the screen = better match (lower SWR).
Higher on the screen = worse match (higher SWR).

The trace shows clear downward dips at the resonant frequencies — these are the “good” spots.

Interpretation of the Dips (Resonances)

J-pole antennas (especially dual-band designs like Ed Fong’s) are not simple dipoles. They consist of a radiating element + a matching stub, so they naturally exhibit multiple resonant modes, including harmonics. This is exactly what you see:

• Left side of the plot (near 144 MHz marker): One or more dips in/near the 2 m band. The marker is placed right at 144.000 MHz (lower edge of the band). The trace near the marker is on the shoulder of a dip, indicating usable (but not necessarily the absolute best) SWR at the very bottom of the band. The main 2 m resonance is likely slightly higher (typical center ~146 MHz).
• Middle of the plot: Several additional dips. These are intermediate/harmonic modes that are normal for this antenna type but usually not used for transmitting.
• Right side of the plot (toward 430–460 MHz): Prominent dip(s) corresponding to the 70 cm band. One of the deeper dips is in this region, showing excellent match where it matters. The trace also trends low again near the right edge (~460 MHz), consistent with another higher-order response.

Between the dips the trace rises high (often off the top of the 1.75 scale) — this is completely normal and expected. You only care about SWR in the actual amateur bands you use.

Overall Performance Assessment

This is a very good result for a dual-band J-pole:

• Multiple deep dips reaching close to the bottom of the scale → SWR very close to 1.0 at the resonant frequencies (excellent match).
• The scale only goes up to 1.75, and the dips are well below that → the antenna is well-tuned for both 2 m and 70 cm.
• Typical real-world Ed Fong J-poles show SWR in the 1.2–1.8 range on both bands when properly built; your scan is right in that ballpark or better.

Quick Summary Table

Frequency Region	Expected Behavior	What You See in the Plot	Quality
144–148 MHz (2 m)	Main resonance	Clear dip(s) near left side	Good to excellent
~200–400 MHz (in between)	High SWR (unused)	Trace high between dips	Normal
430–450 MHz (70 cm)	3rd-harmonic resonance	Prominent dip(s) toward right	Excellent
>450 MHz	Higher-order modes	Trace trending low again	Normal for J-pole

Bottom Line

Your Ed Fong J-pole is performing as designed — it has solid low-SWR resonances in both the 2 m and 70 cm bands. The multiple dips are characteristic of this antenna style and are not a problem.

If you want the exact SWR number at 144 MHz (or any other specific frequency), just move the marker on the NanoVNA and read the value at the top of the screen. You can also narrow the sweep (e.g., 140–150 MHz or 420–450 MHz) for a more detailed view of each band.

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Afterwards, I ran scans but limited the range to 140 - 150 MHz and 450 - 460 MHz, to get more granular views of the 2M and 70cm bands. But this shows how you can use AI to help you understand raw data.