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NanoVNA Antenna Testing

NanoVNA Antenna TestingOverview

A NanoVNA (Vector Network Analyser)Analyzer) allows you to measure SWR, return loss, and impedance of antennas and coax cables. For LoRa mesh work,is the primaryessential usetool isfor verifying antennasantenna areperformance resonantbefore atdeployment. 915It MHzmeasures and identifying cable or connector problems. NanoVNAs are available for $50–$80 and are a worthwhile investment for anyone deploying more than a few nodes.

What SWR Means

SWR (Standing Wave Ratio) measuresand impedance — telling you how well theyour antenna's impedanceantenna is matched to the 50-ohm50 transmissionΩ line.system and whether it is resonant at 915 MHz. A perfect10-minute matchNanoVNA ischeck before mounting an antenna can save hours of troubleshooting range problems later.

Models

ModelScreenFrequency RangePrice NanoVNA-H2.8″50 kHz–1.5 GHz~$30–50 NanoVNA-H44.0″10 kHz–1.5 GHz~$50–70 NanoVNA-F4.3″ (metal case)10 kHz–1.5 GHz~$50–70

Kit includes: NanoVNA unit, calibration standards (Open/Short/Load), two SMA cables, USB-C charging cable.

Five-Step Testing Procedure

Step 1 — Initial Setup

    Charge the NanoVNA via USB-C before first use. Power on. Set the frequency range: START = 850 MHz, STOP = 950 MHz.

    Step 2 — Calibration (Most Critical)

    Calibrate every session or any time you change the frequency range. Calibration compensates for cable and connector losses — skipping it invalidates all measurements.

      Navigate to Menu → CAL → CALIBRATE. Connect the OPEN standard → select OPEN → wait for measurement. Connect the SHORT standard → select SHORT → wait. Connect the LOAD (50 Ω) standard → select LOAD → wait. Save calibration to a slot (0–4). Verify: reconnect LOAD → SWR should read ~1.0:1.0, Higherimpedance ~50+j0 Ω.

      Recalibrate when: changing frequency range; moving to a significantly different temperature environment; switching to different cables.

      Step 3 — Configure Display

        Set Trace 1 to SWR. meansOptionally moreset powerTrace is2 reflectedto backSmith fromChart or R+jX for impedance detail. Add a marker at 915 MHz.

        Step 4 — Connect Antenna

          Connect antenna cable to CH0 (Port 1). Use the antennashortest intopossible cable between the radio.NanoVNA and antenna. Tighten connectors finger-tight only — do not over-torque SMA. Check connector type: LoRa antennas commonly use SMA or RP-SMA. These look identical but are not compatible — verify before connecting.

          Step 5 — Interpret Results

          SWR Ratings

          SWRReturn LossReflected PowerAssessment
          1.0:1∞ dB0%Perfect (theoretical) 1.5:114 dB4%Excellent — acceptable for any use 2.0:19.5 dB11%Good — acceptable for most use 3.0:16 dB25%Marginal — investigate root cause 5.0:13.5 dB44%Poor — replace antenna or cable

          SWR Thresholds for LoRa

            <1.5: Excellent. No action needed. 1.5–2.0: Good. Acceptable for field use. 2.0–3.0: Marginal. Investigate the antenna and connectors. May cause PA stress over time. >3.0: Poor. Replace the antenna, cable, or connectors. High SWR can damage the LoRa module PA in some devices.

            Calibrating the NanoVNA

            Calibration is essential for accurate measurements. The NanoVNA includes an SMA calibration kit (Open, Short, Load, Through). Calibrate at the end of the cable you will use — not at the NanoVNA port itself if you are using a cable extension.

              Set frequency range to 800–1000 MHz to bracket 915 MHz. Connect the Open standard; run calibration step. Connect the Short standard; run calibration step. Connect the 50-ohm Load standard; run calibration step. Save the calibration. Recalibrate any time you change cables.

              Measuring an Antenna

                Calibrate the NanoVNA as above with the measurement cable attached. Attach the antenna to the end of the calibrated cable. On the NanoVNA display, look for the SWR minimum. It should appear near 915 MHz for a properly tuned LoRa antenna. Note the SWR value at exactly 915 MHz. If the minimum is significantly off 915 MHz, the antenna is mis-tuned (common with cheap antennas) and may not perform well on your network.

                Diagnosing Cable Problems

                Coax cable faults (water intrusion, crushed cable, bad connectors) show as unexpected SWR readings. To isolate the problem:

                  Measure SWR with a known-good antenna connected directly to the NanoVNA (no cable). Note the reading. Insert the cable and re-measure. Any significant SWR increase points to cable or connector problems. Flex and bend the cable while watching the NanoVNA. A changing SWR during flexing indicates a broken conductor or intermittent connector.

                  Common NanoVNA Findings

                  FindingLikely CauseRatingAction 1.0–1.5ExcellentDeploy with confidence 1.5–2.0Good — acceptableFine for most deployments 2.0–3.0Marginal — some power lossInvestigate connector quality 3.0+Poor — significant lossReplace antenna or diagnose connector

                  Resonant Frequency

                  The lowest SWR minimumdip wellon the sweep is the antenna’s resonant frequency.

                    Dip at 915 MHz — optimal Dip below 915 MHzAntenna too— antenna is slightly long or(resonates mis-tunedTrimlower) antennaDip if adjustable; replace if fixed SWR minimum well above 915 MHzAntenna too— antenna is slightly short or(resonates mis-tunedExtendhigher) antenna if

                    Common adjustable;Problems replace& ifDiagnosis

                    fixed
                    SymptomLikely Cause High SWR >3 across entire range850–950 MHz bandOpenAntenna tuned for 868 MHz (European band); damaged or shortloose inconnector; cable/connectorInspectmissing andground replaceplane cableon andwhip connectorsantenna SWR varies withwildly / unstable readingLoose connector; damaged cable movementIntermittent— connectorwiggle orconnections brokenwhile conductorRe-crimpwatching or replace connector; replace cabledisplay Excellent SWR changesbut whenpoor rangeSWR measures impedance match only, not gain. A perfectly matched 0 dBi antenna will outperform a mismatched 6 dBi antenna at short range, but not at distance. Evaluate antenna gain separately.

                    PC Software: NanoVNA-Saver

                    NanoVNA-Saver is held

                    Bodyfree, capacitanceopen-source detuningNormalsoftware (Windows/Mac/Linux — search GitHub for handheld“NanoVNA-Saver”) that connects to your NanoVNA via USB and provides:
                      Larger, higher-resolution graphs Data export (CSV) Smith chart display Touchstone (.s1p) file export for import into antenna modeling software Multi-antenna comparison — overlay sweeps from different antennas

                      Common Mistakes to Avoid

                        Skipping calibration — all measurements are invalid without calibration Calibrating at the wrong frequency range — calibration is only valid for the range it was performed at; recalibrate if you change START/STOP Testing indoors near metal objects — nearby metal detuning antennas; test in freethe airopen or simulate the actual mounting environment Using adapters without accounting for comparisonelectrical length —

                        FieldSMA Verificationadapters Without NanoVNA

                        If you do not haveadd a NanoVNA,small youbut canmeasurable stillelectrical verifylength; basicminimize antennaadapter functionuse

                        byConfusing comparing RSSI/SNR values reported by the MeshCore or Meshtastic app when communicating with a known reference node. Compare readings withSMA and withoutRP-SMA the— antenna,SMA andhas betweencenter differentpin antennas,on keepingplug; distanceRP-SMA andhas orientationcenter constant.pin Thison isjack. lessForcing precisemismatched thanconnectors SWRdamages measurementboth. but sufficient for comparative testing.
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