In the forum there were instructions for measuring the scope bandwidth. Does anyone know which thread it was in?
I don’t know the forum post you’re referring to, but for any serious measurement a levelled signal generator is required.
Yet in a pinch you can use a less accurate method that requires no further equipment:
SDS2504X_HD_Base_Noise
This method assumes that the base noise in the scope frontend is white - which isn’t quite true, particularly not for frequencies below 20 MHz. Taking this into account, you just need to use 20 MHz as the reference frequency (instead of 1 MHz).
Most of the settings can be plainly seen in the screenshot:
Input coupling DC with 50 Ω input impedance, 500 µV/div.
Timebase 1 µs/div and AC Line trigger.
An FFT with Flattop window over the full span from 0 – 1 GHz and 1024 times averaging. For a 100 MHz instrument, a narrower span like 500 MHz could be used.
Now we can use tracking cursors to find the frequency where the amplitude has dropped by 3 dB with regard to the reference frequency (20 MHz):
3.07 (ΔY) dB Bandwidth = X2 = 595 MHz;
This result isn’t too far off; the actual bandwidth is about 585 MHz, as measured in max hold mode with a properly swept and levelled signal source:
SDS2504X_HD_FR_2x600s_500uV