Data Smoothing

Data smoothing reduces noise in measurements by averaging adjacent data points. This is useful for noisy measurements or when you need cleaner traces for documentation.

Enable Smoothing

Tap the screen to open the menu
Navigate to DISPLAY > SMOOTH
Select a smoothing level (1-8) or OFF

Smoothing Levels

The smooth factor controls how many adjacent points are averaged:

Level	Points Averaged	Effect
OFF	None	Raw data, maximum detail
1	3	Light smoothing
2	5	Moderate smoothing
3	9	Good noise reduction
4	17	Heavy smoothing
5-8	33+	Very heavy smoothing

How Smoothing Works

The firmware smooths complex S-parameter data (real and imaginary parts independently) by making multiple passes over the sweep points. Each pass applies a 3-point weighted average to adjacent points.

Iteration Count

The smooth factor controls how many passes are applied:

Factor	Passes	Effective Window
1	1 pass	3 points
2	2 passes	~5 points
3	4 passes	~9 points
4	8 passes	~17 points
5	16 passes	~33 points
6	32 passes	~65 points
7	64 passes	~100+ points
8	128 passes	Nearly flat

The formula is 2^(factor-1) passes. At factor 7-8 on a 101-point sweep, the smoothing window approaches the full sweep — effectively flattening the trace.

Smoothing Algorithms

The firmware supports two averaging methods, toggled via CONFIG > SMOOTH MODE:

Arithmetic Mean (default, VNA_MODE_SMOOTH enabled):

Formula: (v_prev + 2*v_current + v_next) / 4
Weighted toward the center point
Best for most measurements — linear averaging preserves amplitude relationships

Geometric Mean (VNA_MODE_SMOOTH disabled):

Uses cube root: cbrt(v_prev * v_current * v_next)
Better preserves multiplicative relationships (dB-scale quantities)
Useful when you want smoothing that behaves linearly in log scale

Boundary Handling

The first and last sweep points are not smoothed — they lack a neighbor on one side, and smoothing them would introduce a phase shift at the sweep edges. This means you may see slightly more noise at the extreme start and end of a sweep compared to the middle.

Smoothing and Sweep Points

Smoothing effectiveness depends on how many sweep points you have:

Device	Max Points	Practical Max Factor
NanoVNA-H	101	4-5
NanoVNA-H4	401	6-7

With 101 points, factor 5 (16 passes) already averages over roughly a third of the sweep. With 401 points, you have four times the resolution budget — factor 6 still preserves meaningful detail.

Shell Commands

# Set smoothing factor (0-8)
smooth 0    # Smoothing off
smooth 1    # Light smoothing
smooth 3    # Moderate smoothing
smooth 5    # Heavy smoothing
smooth 8    # Maximum smoothing

# Query current setting
smooth

When to Use Smoothing

Good Use Cases

Noisy environments: EMI or vibration causing measurement noise
High frequency measurements: Above 500 MHz where noise increases
Documentation: Clean traces for reports or screenshots
Trend analysis: When you need to see overall shape, not fine detail

When to Avoid

Sharp resonances: Smoothing can hide narrow peaks
Calibration: Always calibrate with smoothing OFF
Crystal measurements: Need to see exact peak location
Filter ripple: Smoothing hides passband ripple

Smoothing vs Bandwidth

Both smoothing and bandwidth settings affect noise, but differently:

Setting	Effect	Trade-off
Smoothing	Averages displayed points	Hides sharp features
Bandwidth	Averages at each point during acquisition	Slower sweep

For best results:

First, increase bandwidth (reduce IF bandwidth) for lower noise during measurement
Then apply smoothing if additional noise reduction is needed

Practical Example

Measuring a noisy antenna:

Set bandwidth to 100 Hz for low noise acquisition
Run the sweep
If trace is still noisy, enable smoothing level 2-3
Adjust smoothing level until trace is clean but details remain visible

Status Indicator

When smoothing is enabled, an indicator appears in the status area showing the current smooth factor.