I’m now 100% certain my plug-in is working correctly, I’ve pretty much re-written it in order to get it to work reliably. The original version of the plugin didn’t use the LimeSuite API to calibrate or specify any anti-alias filtering. Also, the metallic sound I mentioned (when listening to the commercial FM radio band) seems to occur whenever one of the 100 MHz harmonic artefacts is located within a station.
Today I had a quick look at the FTDI USB3 device and driver. Interestingly the supplied configuration utility show that the device uses a 100 MHz FIFO clock. I wonder if this is the culprit…
There is a 66 MHz option, but so far I’ve not been able to get this to work, as when selected the device drops down to a single USB channel (the driver appears to require two). Shame, as it would confirm whether or not this is the source of the spurious signals.
If I make any progress I’ll post the outcome here. Any thoughts?
Just for interest here’s a screen shot of the FT60X configuration utility.