Your First S11 Measurement

S11 measures the signal reflected back from Port 1 (CH0). This tutorial walks you through connecting an antenna and interpreting the results.

What You Will Learn

• How to connect an antenna to the NanoVNA-H
• Setting the frequency range for your band of interest
• Reading SWR, return loss (LogMag), and impedance
• Using markers to find resonant frequency

Equipment Needed

• NanoVNA-H or NanoVNA-H4
• SMA cable or adapter for your antenna
• An antenna to measure (any HF/VHF/UHF antenna)
• Calibration kit (if not already calibrated)

Tip

For accurate measurements, calibrate the NanoVNA at the end of your feedline cable before connecting the antenna. See the Full Calibration tutorial.

Connecting Your Antenna

1. Power on the NanoVNA-H

   Connect via USB or use the battery. The sweep will start automatically.

2. Connect the antenna to Port 1 (CH0)

   Port 1 is the SMA connector labeled “CH0” or “S11”. This is the reflection measurement port.

   Caution

   Do not transmit into the NanoVNA. Maximum safe input is approximately +10 dBm (10 mW). Disconnect your antenna from your transmitter before measuring.

3. Verify the connection

   You should see the trace move on screen as the NanoVNA sweeps. If the trace is flat at 0 dB, check your connection.

Setting the Frequency Range

1. Open the Stimulus menu

   Touch the screen to bring up the menu, then select STIMULUS.

2. Set the START frequency

   Select START and enter your lower frequency. For a 2m antenna, enter 140M (140 MHz).

   Use the keypad:

   • Numbers 0-9 for digits
   • M for MHz, k for kHz, G for GHz
   • Touch the checkmark or press the encoder to confirm

3. Set the STOP frequency

   Select STOP and enter your upper frequency. For a 2m antenna, enter 150M (150 MHz).

4. Alternative: Use CENTER and SPAN

   You can also set frequency using CENTER and SPAN:

   • CENTER: 145M (center of the 2m band)
   • SPAN: 10M (10 MHz total span)

Choosing Display Formats

The NanoVNA can display S11 data in several formats. Access these via DISPLAY > FORMAT S11 (REFL).

Most Useful S11 Formats

Format	What It Shows	Good For
LOGMAG	Return loss in dB	Quick assessment of match quality
SWR	Standing Wave Ratio	Familiar metric for antenna work
SMITH	Impedance on Smith chart	Understanding complex impedance
RESISTANCE	Real part of Z	Finding resonance (X=0)
REACTANCE	Imaginary part of Z	Determining if antenna is too long/short

1. Select LOGMAG for return loss

   Go to DISPLAY > FORMAT S11 (REFL) > LOGMAG

   The trace shows return loss in dB. Lower values (more negative) indicate a better match:

   • -6 dB = SWR 3:1
   • -10 dB = SWR 2:1
   • -14 dB = SWR 1.5:1
   • -20 dB = SWR 1.2:1

2. Add an SWR trace

   Enable a second trace: DISPLAY > TRACE > TRACE 2

   Set it to SWR: DISPLAY > FORMAT S11 (REFL) > SWR

   Now you see both return loss and SWR simultaneously.

Using Markers

Markers let you read exact values at specific frequencies.

1. Enable Marker 1

   Touch MARKER > MARKER 1. A marker appears on the trace.

2. Move the marker

   Use the rotary encoder (jog wheel) to move the marker along the trace. The marker readout shows frequency and measured values.

3. Use marker search

   To find the best match point automatically:

   • Touch MARKER > SEARCH > MIN to find the minimum return loss (best match)

4. Read the marker values

   The marker display shows:

   • Frequency
   • Return loss (dB) for LOGMAG trace
   • SWR for SWR trace
   • Impedance (R + jX) in Smith chart mode

Interpreting Your Results

Good Antenna Match

A well-matched antenna shows:

• Return loss better than -10 dB (more negative) at your desired frequency
• SWR below 2:1
• Impedance close to 50 ohms with minimal reactance

Common Issues

Antenna Too Long

Symptoms:

• Resonant frequency is below your target
• Reactance is negative (capacitive) at target frequency

Fix: Shorten the antenna elements

Antenna Too Short

Symptoms:

• Resonant frequency is above your target
• Reactance is positive (inductive) at target frequency

Fix: Lengthen the antenna elements

Poor Match at Resonance

Symptoms:

• Reactance is zero but resistance is not 50 ohms
• SWR minimum is still above 2:1

Fix: Adjust antenna geometry, height, or add a matching network

Example: Measuring a 2m J-Pole

Here is what a typical 2-meter J-pole antenna measurement looks like:

1. Set frequency range: 140 MHz to 150 MHz
2. Enable LOGMAG and SWR traces
3. Place marker at the SWR minimum
4. Expected results for a tuned J-pole:
   • Resonance near 146 MHz
   • SWR below 1.5:1
   • Return loss better than -14 dB
   • Impedance approximately 50 ohms

Saving Your Measurement

To save your measurement data or screenshot:

1. Insert a microSD card (formatted FAT32)
2. Touch SD CARD in the menu
3. Select SCREENSHOT to save an image
4. Select SAVE S1P to save Touchstone data for later analysis

Next Steps

• Reading the Smith Chart - Understand the circular display
• Your First S21 Measurement - Measure insertion loss through a filter
• Tuning an HF Antenna - Detailed antenna adjustment procedure