How to Use a NanoVNA — Complete Guide for Ham Radio Antenna Analysis
A complete practical guide to the NanoVNA vector network analyser for amateur radio antenna work. Covers what a VNA measures and why it matters, the essential calibration procedure, reading SWR and impedance plots, identifying resonance and tuning antennas, measuring velocity factor and cable length, using the Smith chart, time-domain reflectometry for fault finding, and transferring data to a PC for detailed analysis. Includes a velocity factor measurement calculator.
Vector network analyser fundamentals
A vector network analyser measures how RF signals behave in a circuit or at an antenna by sending a known signal and measuring what comes back. Unlike a simple SWR meter — which measures only reflected power magnitude — a VNA measures the complex reflection coefficient at its port. Complex means both magnitude and phase are captured. This dual measurement allows the VNA to compute not just how much signal is reflected but what impedance is producing that reflection — the resistance and reactance components separately.
The NanoVNA is a two-port VNA in a pocket-sized package. Port 1 (CH0) is the reflection measurement port — it transmits a signal and measures its own reflection, from which it derives impedance, SWR, return loss, and Smith chart data. Port 2 (CH1) is the transmission measurement port — it receives signal transmitted through the device under test from Port 1, from which it derives insertion loss, gain, and filter response. For antenna work, Port 1 is used almost exclusively. Port 2 becomes useful for measuring balun insertion loss, filter passband, and cable loss.
S-parameters — S11 and S21 explained
The NanoVNA displays measurements in terms of S-parameters — scattering parameters that describe the ratio of reflected or transmitted wave amplitude to incident wave amplitude at each port. S11 is the reflection coefficient at Port 1: it is a complex number whose magnitude tells you how much of the incident signal is reflected, and whose phase tells you whether the reflected wave is leading or lagging the incident wave — equivalently, whether the load is inductive or capacitive. S21 is the forward transmission from Port 1 to Port 2, which gives insertion loss or gain.
For antenna measurements, S11 is the primary parameter. The NanoVNA derives all its antenna measurements — SWR, return loss, impedance magnitude |Z|, series resistance R, series reactance X, parallel resistance and reactance, and Smith chart position — from the S11 measurement. All of these represent different ways of expressing the same underlying physical quantity: the impedance at the antenna feedpoint relative to the 50-ohm reference impedance of the instrument.
What the NanoVNA cannot do
Understanding the NanoVNA's limitations prevents misinterpretation of results. The NanoVNA measures impedance at its port connector — not at the antenna feedpoint unless the VNA is connected directly at the feedpoint with no intervening cable. A 10-metre coax between the NanoVNA and the antenna transforms the antenna feedpoint impedance to a different value at the VNA port, depending on the electrical length of the cable. The impedance seen at the VNA port is not the same as the impedance at the antenna feedpoint unless the cable is an electrical multiple of a half wavelength, or unless the VNA's port-extension feature is used to mathematically de-embed the cable.
The NanoVNA also cannot measure absolute power, transmitter output, or antenna radiation efficiency directly. A perfect 50-ohm match could represent a resonant antenna efficiently radiating, or it could represent a dummy load. The VNA tells you about impedance, not about radiation. Additionally, the NanoVNA's calibration accuracy degrades at the frequency extremes of its range and is sensitive to temperature and mechanical stress on the calibration standards. For absolute impedance measurements within 1 percent, a laboratory VNA is needed. For the purposes of antenna resonance finding, trimming, and cable measurement, the NanoVNA is entirely adequate.
NanoVNA hardware variants
Multiple NanoVNA versions are available. The original NanoVNA covers approximately 50 kHz to 900 MHz with a small 2.8-inch screen. The NanoVNA-H adds improved dynamic range and a larger battery. The NanoVNA-H4 upgrades to a 4-inch screen, improved calibration stability, and a nominal upper frequency of 1.5 GHz, with practical useful range to around 900 MHz for antenna work. The NanoVNA-F covers 1 MHz to 3 GHz with a larger enclosure. All variants use the same basic operating procedure and firmware interface — differences are primarily in frequency range, dynamic range, screen size, and build quality.
For amateur radio HF and VHF antenna work, any NanoVNA variant is adequate. The NanoVNA-H4 is the most recommended for its screen size and stability. When purchasing, beware of extremely cheap counterfeits that use inferior components and drift significantly with temperature — buy from a reputable source. Genuine units from Hugen or edy555 designs are well-supported with active firmware development. The NanoVNA Saver PC software significantly extends the usability of any variant by providing a large screen, data export, and more detailed analysis tools.
NanoVNA Calibration Procedure (OSL + Through)
Calibration must be performed at the measurement plane — the end of any extension cables used during measurement. Never skip calibration. A miscalibrated NanoVNA gives completely wrong results.
Warm up and set frequency range
Power on the NanoVNA and allow 5 to 10 minutes of warm-up time for frequency stability. Navigate to the Stimulus menu and set the Start and Stop frequencies to bracket your target measurement range. For HF antenna work, set Start to 1 MHz and Stop to 30 MHz. For a VHF antenna, set Start to 100 MHz and Stop to 200 MHz. Set the number of sweep points to 101 or 201 for reasonable resolution — higher point counts give more detail but slower sweeps. Set this frequency range before calibrating, as a calibration is only valid for the range it was performed over.
Attach any extension cable and calibrate at its far end
If you will be measuring an antenna through a short coax extension cable — for example, a 0.5-metre SMA-to-BNC jumper to reach the antenna connector — attach that cable before calibrating. The calibration must be performed at the end of the cable, not at the NanoVNA SMA port. Calibrating at the NanoVNA port and then adding a cable shifts the measurement plane and introduces errors proportional to the cable's electrical length. Attach the calibration standards at the far end of the extension cable — the same connector that will attach to the antenna.
Perform OPEN calibration
Navigate to Calibrate → Calibrate → Open. Leave the calibration port open — nothing connected. Press the OPEN button and wait for the sweep to complete. The NanoVNA measures the reflection from an open circuit, which has a reflection coefficient magnitude of 1 and a phase that varies with frequency due to the fringing capacitance of the open connector. This data is used to correct the measurement for the instrument's source directivity and frequency response.
Perform SHORT calibration
Attach the short-circuit standard — the metal cap supplied with the NanoVNA that shorts the SMA centre pin to the shell, or a purpose-made short standard. Navigate to Calibrate → Short and trigger the measurement. The short circuit has a reflection coefficient magnitude of 1 and a phase of 180 degrees opposite to the open, allowing the instrument to separate different error mechanisms in its error model.
Perform LOAD calibration
Attach the 50-ohm load standard — the precision termination included in the NanoVNA kit. Navigate to Calibrate → Load and trigger the measurement. The 50-ohm load presents zero reflection (S11 = 0) and allows the instrument to characterise and remove its own port mismatch from subsequent measurements. The quality of this 50-ohm standard directly affects calibration accuracy — a 50-ohm resistor with even 1 percent tolerance error reduces calibration accuracy noticeably at higher frequencies.
Perform THROUGH calibration (for S21 measurements)
If you plan to use Port 2 for transmission measurements — measuring filter response, cable loss, or balun insertion loss — connect Port 1 directly to Port 2 with a short SMA-SMA adapter. Navigate to Calibrate → Thru and trigger the measurement. This step is not needed for antenna SWR and impedance measurements using Port 1 only, but is required for any two-port measurement. Skip this step if you are only measuring antennas.
Apply and save calibration
Navigate to Calibrate → Done to apply the calibration corrections. Then navigate to Calibrate → Save and save to one of the available calibration slots — typically Cal 0 through Cal 4. Label the slot in a notebook with the frequency range and date. A saved calibration is automatically loaded when the NanoVNA boots if it was saved to slot 0. Verify the calibration by connecting the 50-ohm load and confirming SWR reads 1.00:1 and R reads 50 ohms across the full sweep range. Any deviation indicates a calibration error — repeat from the beginning.
Coax Velocity Factor Measurement Calculator
Use the NanoVNA to measure the resonant frequency of an open-ended or short-circuited cable stub, then calculate its velocity factor. Connect the cable to Port 1 with the far end open (for first resonance at quarter-wave) or shorted.
The SWR trace — finding resonance
The SWR trace is the most immediately useful display for antenna work. Configure the NanoVNA to show SWR on the primary trace for CH0 (Port 1). Set the display scale so the Y-axis covers SWR 1 to 5 for initial surveys, narrowing to 1 to 2 once resonance is found. Resonance appears as a dip in the SWR trace — the frequency of minimum SWR is approximately the resonant frequency of the antenna. For a correctly built resonant dipole, the SWR minimum should be between 1.0:1 and 1.5:1 at the design frequency.
A useful workflow for trimming a new dipole is to start with the wire cut 5 to 10 percent long, sweep from 1 to 30 MHz, identify the SWR dip, note its frequency, and trim the wire until the dip sits on the target frequency. Each 5mm trim of each arm shifts the resonant frequency up by approximately 20 to 50 kHz depending on the band. Trim conservatively — you cannot add wire back once it is cut. The NanoVNA makes this process dramatically faster than the traditional trim-transmit-check cycle using an SWR meter and transceiver.
The impedance traces — R and X
The R (resistance) and X (reactance) traces give more diagnostic information than the SWR trace alone. At the resonant frequency of an antenna, the reactance X passes through zero — a sign that the inductive and capacitive reactances of the antenna are equal and cancelling. Below resonance the antenna is capacitively reactive (X is negative). Above resonance it is inductively reactive (X is positive). The frequency where X crosses zero is the true resonant frequency, which may differ slightly from the SWR minimum if the feedpoint resistance at resonance is not 50 ohms.
The R trace at resonance shows the feedpoint resistance. A resonant half-wave dipole in free space has approximately 73 ohms feedpoint resistance, which produces SWR of about 1.46:1. A dipole configured as an inverted-V has lower feedpoint resistance — typically 50 to 65 ohms — depending on apex angle. If the R trace shows 35 ohms at resonance, the antenna is a near-quarter-wave element with a missing or inadequate ground system. If R shows 150 ohms at resonance, the antenna may be operating at a second harmonic where the feedpoint impedance is elevated. These diagnoses are impossible from SWR alone and require the R and X traces.
The Smith chart — impedance at a glance
The Smith chart display maps the complex impedance at each frequency to a point on a circular chart. The centre of the chart represents 50 ohms — perfect match. Points to the right of centre represent resistance above 50 ohms. Points to the left represent resistance below 50 ohms. Points above the horizontal centreline represent inductive reactance. Points below represent capacitive reactance. The outer circle represents zero resistance — a purely reactive load.
For antenna work, the Smith chart sweep should produce a trace that crosses the horizontal centreline (X = 0) at the resonant frequency and passes close to the chart centre (50 ohms) at the point of best match. A trace crossing the centreline to the left of centre means feedpoint resistance is below 50 ohms. A trace crossing to the right means feedpoint resistance is above 50 ohms. The Smith chart also reveals the type of matching network needed to transform a given feedpoint impedance to 50 ohms.
Time domain reflectometry — finding cable faults
The NanoVNA includes a TDR function — accessible via the Transform menu — that converts the frequency-domain S11 sweep into a time-domain view of reflections along a cable. Impedance discontinuities along the cable — connectors, kinks, water ingress, or an antenna feedpoint — appear as peaks in the TDR display at a time delay corresponding to their distance from the NanoVNA port. With the cable's velocity factor entered, the TDR display converts time to physical distance, showing the location of each discontinuity in metres from the measurement point.
TDR is invaluable for locating water ingress in buried or wall-routed coax, identifying a bad connector mid-run without opening walls, measuring the electrical length of an unknown cable, and verifying the physical length of a cable against its labelled value. The resolution of the NanoVNA TDR is limited by its frequency range — for finer resolution at short distances, a wider frequency sweep is needed. For most amateur feedline fault-finding applications, the NanoVNA TDR provides sufficient resolution to locate faults within half a metre.
| Task | Display mode | Frequency range | What to look for | Action on result |
|---|---|---|---|---|
| Find dipole resonance | SWR trace CH0 | Band ±20% | SWR minimum dip | Trim wire until dip reaches target frequency |
| Measure feedpoint impedance | R + jX or Smith chart | Narrow around resonance | X crosses zero; note R value | R ≠ 50Ω → consider matching or height adjustment |
| Check multiband antenna | SWR trace, 1–30 MHz | 1–30 MHz full HF | Multiple SWR dips | Verify each dip falls on target band; trim accordingly |
| Measure coax VF | S11 |Z| or SWR | Around expected resonance | Low-Z dip (shorted stub) or high-Z peak (open stub) | Enter measured f and cable length into VF calculator above |
| Check coax for damage | TDR (Transform menu) | 1–300 MHz | Unexpected reflection peak mid-run | Peak location in metres = fault position |
| Measure balun insertion loss | S21 dB, CH1 | Target band | S21 dB value through balun | <0.5 dB at target freq = good; >1 dB = concern |
| Verify ATU match | SWR, CH0 | Operating frequency | SWR at output port of ATU | SWR <1.5:1 = good match; >2:1 = retune ATU |
| Measure choke impedance | S11 |Z| or Smith chart | Target band | |Z| value at operating frequency | >1,000 Ω = adequate choke; <500 Ω = insufficient |
| Measure filter response | S21 dB, CH1 | Full filter range | Passband loss + stopband rejection | Compare to filter specification |
| Identify cable electrical length | TDR or stub resonance | Wide HF sweep | TDR delay or stub resonance frequency | Calculate electrical length from time delay × VF × c |
Why use NanoVNA Saver
NanoVNA Saver is free open-source PC software that connects to the NanoVNA over USB and provides a large-screen interface with enhanced measurement capabilities. It offers higher sweep point counts — up to 10,000 points versus 201 on the device — producing finer frequency resolution for detailed impedance characterisation. It displays multiple trace types simultaneously on large format plots, exports data to CSV for spreadsheet analysis, and saves calibration files that can be reloaded without repeating the hardware calibration procedure on the device.
For precise antenna work — finding the exact resonant frequency of a narrow-bandwidth magnetic loop, characterising a trap antenna across multiple bands, or generating publication-quality impedance plots — NanoVNA Saver is substantially more capable than the device screen alone. The TDR function in NanoVNA Saver is also more configurable than the on-device TDR, allowing the velocity factor to be set precisely and the time-domain window function to be adjusted for the best resolution-versus-sidelobe trade-off.
Connecting and configuring NanoVNA Saver
Download NanoVNA Saver from its GitHub repository — search for NanoVNA-Saver by NanoVNA-Users organisation. Install and launch. Connect the NanoVNA to the PC via the USB cable supplied. In NanoVNA Saver, click the serial port dropdown and select the COM port assigned to the NanoVNA. Click Connect. The software reads the current calibration and sweep data from the device and displays them immediately.
The calibration workflow in NanoVNA Saver allows performing the full OSL calibration from within the software, storing calibration data on the PC rather than the device's limited memory slots. This is particularly useful when working with multiple frequency ranges — store separate calibration files for 1–30 MHz HF, 100–200 MHz 2m, and 400–500 MHz 70cm, loading the appropriate file for each measurement session. The software also supports averaging multiple sweeps to reduce noise, which is valuable when measuring very low-impedance loads or near the instrument's dynamic range limits.
Exporting and interpreting data
NanoVNA Saver can export S-parameter data in Touchstone (.s1p, .s2p) format, the standard interchange format for VNA data importable into antenna modelling software, RF simulation tools, and analysis packages. It can also export CSV files containing frequency, R, X, SWR, and |Z| values suitable for direct import into spreadsheets. The exported data allows offline analysis, comparison of measurements taken at different times or antenna configurations, and production of annotated plots for logging purposes.
A practical workflow for antenna development is to save a baseline Touchstone file when the antenna is first resonated, then compare subsequent measurement sessions against the baseline. SWR plots that have drifted from baseline indicate physical changes — connector corrosion, water in coax, wire movement, or nearby structure changes. This systematic comparison approach is far more sensitive to gradual degradation than relying on memory of what the SWR looked like months ago.
Port extension and de-embedding
The port extension function in NanoVNA Saver mathematically compensates for a known length of cable between the calibration plane and the actual measurement point. If the NanoVNA was calibrated at its SMA port but is connected to an antenna through 10 metres of coax, entering the electrical length of the coax into the port extension dialog shifts the measurement plane to the far end of the cable, showing the antenna feedpoint impedance rather than the transformed impedance at the VNA port.
Port extension accuracy depends on knowing the electrical length of the cable precisely, which requires knowing its velocity factor — another reason the VF measurement procedure above is useful. For routine antenna work, directly calibrating at the antenna end of the cable is simpler and more accurate than port extension. Port extension is most useful when the cable is fixed and it is inconvenient to transport the calibration standards to the antenna location.
How accurate is the NanoVNA for antenna measurements?
For finding resonant frequencies, trimming antennas, and comparing SWR before and after changes, the NanoVNA is entirely adequate. Absolute impedance accuracy is typically within 2 to 5 percent at mid-HF frequencies after good calibration, degrading toward the frequency extremes. For identifying whether an SWR dip is at 14.150 or 14.200 MHz the NanoVNA is accurate enough. For measuring a 50-ohm load to verify it is exactly 50.0 ohms, a laboratory instrument is required.
Do I need to recalibrate every time I use the NanoVNA?
Not necessarily. A calibration stored in slot 0 is loaded at boot. If the NanoVNA has not been physically disturbed, the temperature has not changed significantly, and you are using the same frequency range and cables as the stored calibration, the stored calibration remains valid. For critical measurements, recalibrate. If results look obviously wrong — SWR reads 3:1 on a known good 50-ohm load — recalibrate immediately.
Why does my SWR look different on the NanoVNA versus my rig's meter?
Several factors cause this discrepancy. The rig's SWR meter uses a directional coupler sampled at transmit power levels; the NanoVNA uses a very low-level test signal. Harmonics and IMD from the transmitter affect the rig's SWR meter. Most importantly, the NanoVNA is calibrated to a reference plane while the rig's meter is at a different point in the RF chain. Both instruments can be correct simultaneously — they are measuring at different points with different reference impedances and signal levels.
Can the NanoVNA damage my antenna or transceiver?
No. The NanoVNA transmits an extremely low-level test signal — typically −13 dBm (50 microwatts) or less — which cannot damage any antenna or passive component. It should not be connected to a transmitter output that is actively transmitting, as the transmitter's power level will damage the NanoVNA's sensitive receiver circuits. Always ensure the transceiver is off or disconnected before connecting the NanoVNA to the feedline.
What is the Smith chart actually useful for?
The Smith chart is most useful for visualising how impedance changes with frequency and for planning matching networks. For antenna work it tells you at a glance whether an antenna is inductive or capacitive at a given frequency, which direction to trim wire, and approximately what matching network topology would produce a 50-ohm match. Many operators find the R + X linear traces more intuitive for routine antenna work and use the Smith chart only for matching design.
How do I measure the resonant frequency of a trap?
Connect the trap in series between Port 1 and Port 2 — the trap acts as a series resonant circuit. Sweep across the expected resonant frequency. The transmission S21 will dip sharply at the trap resonant frequency where the trap's impedance peaks and maximum attenuation occurs. Alternatively, connect the trap across Port 1 with a 50-ohm termination to ground — the impedance will peak at resonance, visible as a peak in |Z| on the S11 display.
Can I use the NanoVNA to measure antenna radiation efficiency?
Not directly. The NanoVNA measures impedance but cannot distinguish between resistance that is radiating RF energy and resistance that is dissipating it as heat. A 50-ohm resistive load and a 50-ohm resonant antenna look identical on the NanoVNA. Radiation efficiency measurement requires comparison methods using known reference antennas and field strength measurements, or antenna modelling software that includes ground loss models.
What is the best NanoVNA firmware to use?
For the NanoVNA-H4, DiSlord firmware is widely regarded as the most stable and feature-complete. It adds improved calibration algorithms, better display options, enhanced TDR, and supports the extended frequency range of the H4 hardware. Check the NanoVNA-Users GitHub for the current recommended version for your specific hardware variant. Do not flash firmware intended for a different hardware variant.