Marker Search

Marker search functions automatically position markers at points of interest such as peaks, minimums, or specific values. This speeds up measurements and improves accuracy.

Search Functions

Access search functions via MARKER > SEARCH:

Function	Action
MAX	Move marker to maximum value
MIN	Move marker to minimum value
PEAK	Find local peak near current position
LEFT	Search left for next peak/crossing
RIGHT	Search right for next peak/crossing

Find Maximum Value

1. Ensure a marker is active
2. Go to MARKER > SEARCH
3. Tap MAX
4. The marker moves to the highest point on the trace

Useful for:

• Finding filter passband center
• Locating S21 transmission peak
• Finding amplifier gain maximum

Find Minimum Value

1. Ensure a marker is active
2. Go to MARKER > SEARCH
3. Tap MIN
4. The marker moves to the lowest point on the trace

Useful for:

• Finding antenna resonance (minimum SWR or S11)
• Locating filter notch frequency
• Finding transmission minimum

Tip

For antennas and SWR measurements, use MIN search to quickly find the resonant frequency.

Peak Search

The PEAK function finds a local maximum near the current marker position:

1. Position marker roughly near the peak of interest
2. Go to MARKER > SEARCH > PEAK
3. The marker moves to the exact peak location

This uses bilinear interpolation for sub-point accuracy.

Left/Right Search

Search left or right from the current marker position:

Search Left

1. Position marker at a reference point (like a peak)
2. Go to MARKER > SEARCH > LEFT
3. The marker moves to the next significant point to the left

Search Right

1. Position marker at a reference point
2. Go to MARKER > SEARCH > RIGHT
3. The marker moves to the next significant point to the right

These searches find threshold crossings, useful for:

• Finding -3 dB bandwidth points
• Locating filter edges
• Finding zero-crossing points

Automatic Tracking

Enable continuous peak tracking:

1. Go to MARKER > TRACKING
2. Select tracking mode:
   • MAX - Track maximum value
   • MIN - Track minimum value
   • OFF - Disable tracking

When tracking is enabled, the marker automatically moves to the peak/minimum after each sweep.

Note

Tracking is useful for monitoring resonant frequency changes in real-time, such as when tuning an antenna.

Practical Examples

Find Antenna Resonance

1. Connect antenna to CH0
2. Set S11 format to SWR or LogMag
3. Go to MARKER > SEARCH > MIN
4. Marker moves to resonant frequency

Measure Filter -3 dB Bandwidth

1. Set S21 LogMag format
2. Use MARKER > SEARCH > MAX to find passband center
3. Enable marker 2 at the same position
4. Use MARKER > SEARCH > LEFT to find left -3 dB point
5. Enable marker 3
6. Use MARKER > SEARCH > RIGHT to find right -3 dB point
7. Bandwidth = Marker 3 frequency - Marker 2 frequency

Monitor Resonance While Tuning

1. Set S11 LogMag format
2. Enable marker at resonance
3. Go to MARKER > TRACKING > MIN
4. As you adjust the antenna, marker follows the resonance
5. Watch the frequency readout change in real-time

Search Algorithm Details

The firmware implements search in three distinct ways:

MAX/MIN — Linear Scan

Scans all sweep points and keeps the index with the highest (or lowest) value. Simple and always finds the global extremum. The search direction (maximum vs minimum) is toggled in CONFIG > MODE > SEARCH — this setting is labeled MAXIMUM or MINIMUM and controls whether the firmware’s internal compare function uses > or <.

PEAK — Interpolated Peak Finding

Finds a local peak near the current marker position using bilinear interpolation between adjacent points. This gives sub-point frequency accuracy — the reported frequency is more precise than the sweep point spacing would normally allow.

For a 101-point sweep across 100 MHz (1 MHz/point), peak interpolation can resolve the peak center to roughly 100 kHz accuracy.

LEFT/RIGHT — Threshold Crossing Search

Searches from the current marker position in the specified direction, looking for where the trace crosses a target threshold. The firmware uses this internally for finding -3 dB bandwidth points, zero crossings, and filter edge detection.

The search walks point-by-point from the current index, comparing each value against a target. When it finds a crossing, it reports the index. This is the mechanism behind the automatic bandwidth measurement in the filter analysis tool.

When Search Fails

Search can fail or give unexpected results when:

Symptom	Cause	Fix
MAX finds wrong peak	Multiple peaks, finds global max not local	Position marker near the peak first, use PEAK instead
LEFT/RIGHT jumps to edge	No crossing exists in that direction	Widen the sweep range or check scale
MIN finds noise floor	Trace dips below measurement floor	Reduce sweep span or increase IF bandwidth
Search doesn’t move marker	Marker already at the extremum	Expected behavior — the search succeeded

Search and Sweep Points

Search accuracy depends directly on sweep point density:

Points	Frequency Step (100 MHz span)	Best For
101	1.0 MHz	Antennas, broad features
201	0.5 MHz	Moderate resolution
401	0.25 MHz	Narrow filters, crystals

For narrow-band devices like crystals (bandwidth measured in kHz), use the maximum sweep points your device supports and narrow the span. On a NanoVNA-H with 101 points, a 1 MHz span gives 10 kHz resolution — adequate for most crystal measurements.

Shell Commands

Search functions are accessed through the marker and measure commands:

# Enable tracking
config mode 1    # Enable search mode

# Use measure command for analysis modes
measure none     # Disable
measure lc       # LC match analysis

Caution

Search functions operate on the currently active trace. Make sure the correct trace and format are selected before searching.