What is a VNA?

A Vector Network Analyzer (VNA) is an instrument that measures how RF signals behave when they encounter your antenna, filter, or other RF component. Unlike a simple SWR meter that only tells you “how much” signal is reflected, a VNA tells you both the magnitude and phase of the signal---giving you a complete picture of what is happening at RF frequencies.

Why “Vector”?

The word “vector” refers to how the VNA measures signals. When an RF signal hits your antenna, some of it radiates (what you want) and some reflects back (what you do not want). That reflected signal has two properties:

• Magnitude: How much signal bounced back (expressed as return loss in dB or as SWR)
• Phase: The timing relationship between the outgoing and reflected signals (expressed in degrees)

Together, magnitude and phase form a “vector”---a complete description of the reflection. This is crucial because phase information lets you calculate the actual impedance of your antenna or device, not just whether it is “good” or “bad.”

Real-World Analogy

Think of throwing a ball against a wall. A simple meter only tells you the ball came back. A “vector” measurement tells you both how hard it came back AND exactly when it arrived---enough information to figure out where the wall is and what it is made of.

What Can You Measure?

The NanoVNA-H measures two fundamental quantities:

S11 (Reflection)

How much signal reflects back from Port 1. Connect your antenna here to measure SWR, impedance, and resonant frequency.

S21 (Transmission)

How much signal passes through from Port 1 to Port 2. Use this to measure filter response, cable loss, and component gain/attenuation.

Common Ham Radio Applications

Antenna Analysis

The most common use: connect your antenna feedline to Port 1 (CH0) and see:

• SWR across the band
• Resonant frequency (where X = 0)
• Actual impedance (R + jX) at any frequency
• Whether the antenna is too long or too short (inductive vs capacitive)

Filter Testing

Connect Port 1 to the filter input and Port 2 to the filter output to see:

• Passband (frequencies that get through)
• Stopband (frequencies that are blocked)
• Insertion loss (how much signal you lose in the passband)
• Rolloff (how quickly the filter cuts off)

Cable Testing

Measure feedline characteristics:

• Velocity factor (how fast signals travel in the cable)
• Cable loss at different frequencies
• Locate faults using Time Domain Reflectometry (TDR) mode

Component Measurement

Measure inductors, capacitors, and crystals:

• Inductance and capacitance values
• Q factor (quality factor)
• Crystal parameters for filter design

How the NanoVNA-H Works (Simplified)

flowchart LR
  A[Signal Source<br/>Si5351] --> B[Port 1<br/>CH0]
  B --> C[Device Under Test]
  C --> D[Reflected Signal]
  D --> E[Mixer + ADC]
  C --> F[Port 2<br/>CH1]
  F --> G[Transmitted Signal]
  G --> E
  E --> H[DSP Processing]
  H --> I[Display]

1. Generate: The Si5351 chip creates a test signal at the frequency you specify (50 kHz to 1.5+ GHz)
2. Apply: The signal goes out Port 1 (CH0) to your device under test
3. Measure: The NanoVNA captures both the reflected signal (S11) and any signal that passes through to Port 2 (S21)
4. Calculate: Digital signal processing extracts the magnitude and phase
5. Correct: Calibration data removes systematic errors from cables, connectors, and the VNA itself
6. Display: Results appear as traces on the Smith chart, graphs, or numeric readouts

VNA vs Other Instruments

Instrument	Measures	Phase Info	Impedance	Frequency Sweep
SWR Meter	Forward/Reflected Power	No	No	No
Antenna Analyzer	SWR, Z	Sometimes	Yes	Limited
Vector Network Analyzer	S11, S21	Yes	Yes	Yes
Spectrum Analyzer	Signal Level	No	No	Yes (receive only)

Why Phase Matters

Two antennas can have identical SWR readings but completely different impedances. Only by knowing the phase can you determine whether your antenna is too long (capacitive) or too short (inductive)---and by how much.

The NanoVNA-H Advantage

Traditional VNAs cost thousands of dollars and require extensive training. The NanoVNA-H brings vector network analysis to every ham shack:

• Portable: Battery-powered, fits in your hand
• Affordable: A fraction of professional VNA cost
• Capable: Measures from 600 Hz to 1.5+ GHz (with harmonics to 2 GHz)
• User-friendly: Touchscreen interface, no computer required
• Accurate: Proper calibration yields professional-grade results

What You Will Learn

The following concept pages build on this foundation:

• S-Parameters: The mathematical language VNAs use (S11, S21, return loss, insertion loss)
• Smith Chart: The powerful circular display that shows impedance at a glance
• Impedance and Q: Understanding resistance, reactance, and component quality
• Calibration: Why and how to calibrate for accurate measurements

Calibration is Key

A VNA is only as accurate as its calibration. Before any serious measurement, you must calibrate with known standards (Short, Open, Load, and optionally Thru). See the calibration guides for step-by-step instructions.

Next Steps

Ready to understand the measurements? Continue to S-Parameters to learn the language of network analysis.