Widebandantenna

gpr

open source ground penetation radar,

princible

┌──────────┐ ┌─────────┐ ┌─────────┐ ┌──────────┤ VNA │.s2p│ tdr.py │.DZT│ viewer: │ ▼ ┌──►│(NanoVNA) |───►│ ├───►│ GPRPy │ ──── ──── │ │ │ │ │ │ Ant1 Ant2 └──────────┘ └─────────┘ └─────────┘

hardware interfaces

based on RaspberryPi 3 or 4

USB NanoVNA

GPIO 08 SDA (I2C) => Display (displays measurement number)
GPIO 09 SCL (I2C) => Display (displays measurement number)
GPIO 26 switch to 3.3V, external pull down => activates measurement
GPIO 17 buzzer => indicating active measurement

usage

• start worker.py on startup, see config section in worker.py
  • config in worker.py, enable/disable modules
  • set path for patched nanovna-saver, adjust freuqency range
  • if rpi is disabled, start worker.py to start measurement, crtl+c for ending, no automatic postprocessing

Requirements

• patched nanovna-saver with parameter interface for headless operation https://github.com/spel-oe/nanovna-saver
• i2c activated on raspberry
• pip3 install:
  • numpy
  • scikit-rf
• imagemagick for preview image
  for pdf conversion support: sudo sed -i '/disable ghostscript format types/,+6d' /etc/ImageMagick-6/policy.xml

For file transfer:

• dnsmasq for AP (dhcp server)
• hostapd for AP (wifi access point)
• http server - if http is enabled in worker.py, file listing is provided on port 8080

Viewing the data

• GPRPy (optional )
  https://nsgeophysics.github.io/GPRPy/
  https://github.com/NSGeophysics/GPRPy
• if gprpy is installed and enabled in worker, a preview image is provided in out/images

wifi_ap

simple accesspoint using dns-catch all as captive portal for easy data access

files and directories:

• documentation/ hardware documentation and example files
• out/ contains processed input files (.DZT), webserver points here
• out/images contains preview images if enabled in worker.py
• wifi_ap/ example config files for wifi access point
• worker/ contains the raw touchstone files one folder each measurement, with ascending number
• beep.py lib: triggers beep as metronom during measurements
• display.py lib: controls the oled display with font file and oled lib
• FreeSans.ttf lib: font for oled display
• gprpy_img.py generates preview png-image out of .DZT file (standalone -h for help)
• lib_oled96.py lib: for small i2c oled display
• LibreVNA_Class.py lib for LibreVNA
• librevna.py saves s2p files from librevna experimental (standalone -h for help)
• README.md this file
• tdr.py converts touchstone (.s2p) files to gpr .DZT file (standalone -h for help)
• worker.py script that orchestrates everything

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TODO

• maybe apply file based calibration for s2p files before tdr.py
• librevna haeadless operation
• example files and pictures

Hardware

Antenna

Antenna design based on https://www.mdpi.com/1424-8220/19/5/1045/pdf?version=1551428447
see documentation/antenna (KiCad 6)

overall setup

• antennas
  • sma cables, short as possible
• shielding boxes, including absorptive material
• vna, e.g. nanovna v2
• pc, e.g. debian based, RaspberryPi 3, 4 or equivalent, pinout see above
  • oled display (i2c) 0,96'' 128x64 pixel
  • beep, buzzer just supply voltage for beep
  • switch, switching measurement on/off
• usb power pack > 30Wh