NanoVNA Versions Save

• fix sign of group delay

• make group delay trace format work
• support negative time value
• remove close menu item
• minor fixes

• change toggle behavior of trace menu and marker menu
• add transform command to change mode of TDR
• add threadshold command
• remove cal glitch between different harmonic modes
• NanoVNA-saver in multisegment mode shall work well

Needs touch calibration and save it after flashing firmware.

• in-device TDR support (contributed by @cho45)
• add scan command for multisegment scan excess 101 points
• fixed invalid sweep at the narrow span (<5kHz)
• fixed failures caused by a race condition between USB and measuring loop
• find device automatically in python script

• use gcc-8.2.1 to build firmware
• contributed by cho45
  • add screen capture command (use script ./python/nanovna.py -C)
  • add trace format of real/imag/impedance/reactance
  • add battery indicator (needs install D2. any small diodes are suitable. 1N4148WS or B5817WS is the best. see https://lowreal.net/2019/09/09/1)
  • add version info screen
  • add menu and command to enter dfu mode
  • add menu item to calibrate touch screen and test it
  • optimize line drawing
  • reduce sram usage

• support 900MHz x3 harmonic operation
• add experimental x5 harmonic
• adjust gain and drive strength of LO
• add sample command to evaluate IF amplitude and dynamic range
• add version command
• rearrange menu to reduce clicks
  • split save and restore
  • trace and marker menu
• remove glitch at first point in sweep span
• interpolate only when cal applied
• add visual feedback on correction/pause menu item
• add n, p key in number pad screen for electrical delay
• fix the mistake of error correction formula for s11
• fix the mistake of the impedance calculation formula