About differences TDR and VNA TDR https://incompliancemag.com/time-domain-measurement-tdr-or-vna/ https://coppermountaintech.com/what-is-the-difference-between-tdr-and-vna-time-domain-measurement/ Als

By default at startup always load 0 calibration slot But if select config->expert settings->remember state (and save config, config->save) NanoVNA store several settings in backup registers and use it

Exist USB isolators on ADUM3160 try search it https://aliexpress.ru/item/1005002959825296.html?sku_id=12000022964317764&spm=a2g2w.productlist.search_results.0.48497f1aAGtFNW

No, measure module in NanoVNA not provide any API on console, just display You can read measured data and calculate on CPU side

Check SI5351 generator I2C bus exchange

No, but LiteVNA support SD Card->Cardreader mode LiteVNA visible as external flash drive and allow direct read/write files

On my firmware not need reset, device always collect RAW data on calibration If frequency range equal old calibration, new calibration data overwrite old. If frequency range different, all old calibra

Depend from option in MARKER->SEARCH, Maximum or Minimum: auto jump on selected trace Max or Min position

This board not original H4 (and possible not work sd card if install slot)

Not understand where you get this code. From plot.c //************************************************************************************** // LINEAR = |S| //*****************************************

Try use USB2 port for update, on some computers USB3 very slow in DFU mode

No, Port2 mismatch very small and in most cases enable ER allow get more better results

ENHANCED RESPONSE calibration method allow fix DUT and port 2 mismatch on measure S21 But on Nanovna due to RAM limits not added Port 2 match compensation (on LiteVNA added full ER calculation)

Made NanoVNA-H/H4 v1.2.40 release https://github.com/DiSlord/NanoVNA-D/releases/tag/v1.2.40 VNA Added Enhanced Response calibration (but not compensate Port 2 impedance, due to memory limits) Separate

Last NanoVNA-H (ST_SM on hardware text on back) use ST7789V lcd module, and need firmware correction, soon I provide universal firmware vs support old ili9341 and new st7789v

Used differential mode codec input

NanoVNA-H use Cortex M0 MCU and allow only 32 bit accumulator for processing. For prevent overflow values divided H4 use hardware DSP and 64 bit accumulator calculate_gamma function just divide comple

XTAL measure Rl - Resistance of one side to the crystal (50Om for nanoVNA or 12.5 Ohm when using adapter) https://www.ph2lb.nl/blog/index.php?page=xtal-adapter-for-nanovna L/C match https://leleivre.c

Negative effects are present at the 12kHz intermediate frequency and its harmonics (in the measure bandwidth around point, so they can be reduced by reducing it)

Just calibrate at the end of this cable But be careful in interpolation mode (when changing the measurement range without calibration), a long cable and interpolation can give incorrect results