trace command hung

[d51r3verse]

qrp73/NanoVNA-Q#16
Same issue appeared latest(f6f948b) NanoVNA-H too.

I using "empty trace" command for identify current trace status and scale in my script.
But it will hung occasionally.
I found the only way to remove this issue, Manually reconfigure traces or simply disable unsued trace slot( trace x off ) before send "empty trace". Similar issues on marker too.

Another issue I found was...

1. Set sweep range to full span 10e3 ~ 1.5e9 / calibrate off / Nothing connected CH0/CH1.
2. trace all off -> marker 1...4 off -> pause (Blank screen / LED steady - For fast fetch)
3. Python loop scan&data 0..1 -> Join&save s2p touchstone via scikit-rf
   Exported every data 0...1 and sp2 files was exactly same.

But data is different with sweep&trace 0..1 enabled.( +4 ~ +20 dB point appeared at CH0 logmag )
NanoVNA requires at least one activated trace for get valid data?

Always appreciate your contribution.

[hugen79]

Do not use the "pause" command to pause the scan. You can use the "scan" command to pause the screen display and perform a single scan, then use the "data" command to get the data.

[d51r3verse]

I issued single pause command at outside of the loop.
Inside the loop doing scan & data 0...1, Every iterated data array were different( data array only updates after scan command )

In device live mode( trace 0 logmag 0 enabled / live sweep ), pulled CH0 logmag can not up to -21 dB( As I expected ).
But, I can see plus level of CH0 logmag when I turned all off traces & markers( blank screen / manual scan via PC ).