by **AndrewA** » Thu May 14, 2015 12:14 pm

The FFT calculations work by using the full bandwidth from 0 to the displayed frequency which is based on the sample rate.

Even if picoscope software could be set to display say from 40-60MHz it would still use the 0-60MHz bandwidth of the scope. So you need to use the zoom function. In your case you could type in a zoom of x100 into the zoom box, and scroll to 44-45MHz, with the frequency on 200MHz.

You can display sampling and FFT information by opening the properties window ("Views" menu, "View Properties")

Here is some more information about the spectrum mode -

At low frequencies, the update rate is slower than at high frequencies as it takes longer to capture the required number of data points for a particular frequency resolution. There is a trade-off between update time and frequency resolution on screen. A high number of "Spectrum Bins" selected (16384?) which will give you, for instance, a frequency resolution (Bin Width) of 305.2mHz on the 5kHz range and a refresh rate (Time Gate) of 3.277 seconds. To get a faster refresh rate, please got to the spectrum options pull-down menu (to the right of the spectrum button) and change the number of bins to, say, 1024. This will give you a refresh rate of 204.8ms, and a frequency resolution of 4.883Hz You may find it useful to keep the "Properties" window open where all these parameters will be permanently displayed.

Regards Andrew

Technical Specialist