Some days ago I received a parcel from my friend Silvio, DM9KS. There was a 20m QRP band-pass filter from QRP Labs inside. I then built the kit as it was there anyway. I did not wind the torroids very accurate, but I have an insertion loss of 2.1 db only on 20m and I have -53db attenuation on 40m and -32db on 15m. I would say great piece of kit! Silvio also told me, that some guys use their Raspberry Pis as a 10mW WSPR beacon. So I connected the filter to my Pi to see what happens.