Probably someone tried to measure amplifier with this nanovna and it's CH1 input is burned out. Another possible root of cause - incorrect channel setting for trace.
In order to check, do the following:
1) Open CAL menu and press RESET
2) Open DISPLAY - TRACE and select blue TRACE1, make sure it is enabled
3) return back to DISPLAY menu and open CHANNEL menu and select CH1 THROUGH
4) return back to DISPLAY menu and open FORMAT menu and select LOGMAG
5) try to connect/disconnect CH0 with CH1 with cable and check if blue trace has significant change
if you performed these steps and blue trace does not respond on cable between CH0 and CH1, then your CH1 input doesn't works.
