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NanoVNA-H NanoVNA-H Documentation

Screenshots

The NanoVNA-H can capture screenshots of the current display for documentation, troubleshooting, or sharing measurement results.

Capture to SD Card

Section titled “Capture to SD Card”
  1. Set up your measurement and display as desired
  2. Tap the screen to open the menu
  3. Navigate to SD CARD
  4. Tap CAPTURE or SCREENSHOT
  5. The screen is saved to the SD card

The image is saved in BMP format with an auto-generated filename.

File Format

Section titled “File Format”

Screenshots are saved in BMP format:

  • Resolution: 320x240 (NanoVNA-H) or 480x320 (NanoVNA-H4)
  • Color depth: 16-bit RGB565
  • Filename: Sequential numbering (e.g., CAPTURE001.BMP)

TIFF Format (Optional)

Section titled “TIFF Format (Optional)”

Some firmware versions support TIFF format with RLE compression:

  • Smaller file size than BMP
  • Enable via configuration if available

Capture via USB

Section titled “Capture via USB”

Capture screenshots from a connected computer:

Shell Command

Section titled “Shell Command”
Terminal window
capture

This sends raw pixel data over USB. Use PC software to decode:

With NanoVNASaver

Section titled “With NanoVNASaver”
  1. Connect NanoVNA-H via USB
  2. Open NanoVNASaver
  3. Click the screenshot/capture button
  4. Save the image file

With Python

Section titled “With Python”
import serial
import struct
from PIL import Image


# Connect to NanoVNA
ser = serial.Serial('/dev/ttyACM0', 115200)


# Request capture
ser.write(b'capture\r\n')


# Read pixel data (320x240x2 bytes for 16-bit RGB)
data = ser.read(320 * 240 * 2)


# Convert to image (RGB565 to RGB888)
# ... (conversion code needed)

RLE Compressed Capture

Section titled “RLE Compressed Capture”

For faster transfer over USB, use compressed capture:

Terminal window
capture 1

This sends RLE-compressed 8-bit palette data:

  • Smaller transfer size
  • Faster capture
  • Requires decoding on PC side

Practical Uses

Section titled “Practical Uses”

Documentation

Section titled “Documentation”
  1. Set up the measurement showing key data
  2. Adjust scaling for clarity
  3. Capture screenshot
  4. Include in documentation or reports

Troubleshooting

Section titled “Troubleshooting”
  1. Reproduce the issue on screen
  2. Capture the display state
  3. Share screenshot for remote assistance

Before/After Comparison

Section titled “Before/After Comparison”
  1. Capture “before” screenshot
  2. Make adjustments (tuning, modification)
  3. Capture “after” screenshot
  4. Compare the two images

Tips for Good Screenshots

Section titled “Tips for Good Screenshots”

Shell Commands

Section titled “Shell Commands”
Terminal window
# Capture raw (16-bit RGB)
capture


# Capture RLE compressed (if supported)
capture 1


# List captured files on SD card
sd_list *.BMP

Retrieving Screenshots

Section titled “Retrieving Screenshots”

From SD Card

Section titled “From SD Card”
  1. Power off NanoVNA-H
  2. Remove SD card
  3. Insert in computer card reader
  4. Copy BMP files

Via Serial Command

Section titled “Via Serial Command”
Terminal window
# List files
sd_list *.BMP


# Read a specific file (outputs binary data)
sd_read CAPTURE001.BMP

File Management

Section titled “File Management”

Screenshots accumulate on the SD card. Periodically:

  1. Transfer files to computer
  2. Delete from SD card using file browser or sd_delete command
Terminal window
# Delete a screenshot
sd_delete CAPTURE001.BMP

Limitations

Section titled “Limitations”
  • No PNG or JPEG support (BMP/TIFF only)
  • Files saved to root directory only
  • Sequential naming only (no custom names from device)
  • SD card required for on-device capture