I recently got a Siglent SDS1204X-E with the SAG1021 AWG addon. Almost everything works well, but there's a very annoying problem with the bode plot function that I'm pretty sure is a firmware bug.
I'm using a very simple test setup, where I have the AWG output going through a piece of RG58 to a tee on channel 1, which also goes through a second piece of RG58 to a 50 ohm terminator on channel 2:
When I run a bode plot, the first sweep after I press the run button comes out fine. But if I let it loop around back to the start frequency, the second and subsequent sweeps have significant glitches in both the frequency and phase plots:
That's a 14db spike in the amplitude! I've also attached the csv data file from the scope that corresponds to this run.
EDIT: 14db is the biggest glitch I've seen so far. Usually the glitches are smaller, more like 1-6db, sometimes positive and sometimes negative.
At first I thought it might just be loose connections, but it's very reproducible and only happens on the second and subsequent frequency sweeps. Pressing the run button again to stop it and then restarting the sweep makes it work again for one more sweep.
I tried it with various sweep settings (e.g. 20hz to 20Mhz at 20 points/decade, and 100hz to 1khz at 100 points/decade) and it's pretty consistent. Now here's the interesting part: the glitches always happen right after the scope timebase (as indicated in the upper left of the screen) changes. The three problematic switches are where it goes from 100ms/div to 50ms, 50ms to 20ms, and 20ms to 10ms.
That sure sounds like a bug to me. My guess is there isn't enough delay after the scope switches timebases before it tries to take a measurement. Unless I'm the one doing something stupid?
Versions:
SDS1204X-E firmware version 6.1.33, hardware version 01-03
SAG1021 firmware version 1.02, hardware version 0-3-1