The Simple Pico Rx is my minimalist implementation of Jonathan Dawson's "Pico Rx" at 101things:  https://github.com/dawsonjon/PicoRX

In this basic form the receiver consists of a Quadrature Sampling Detector (QSD aka Tayloe) and the Pico2 MCU which handles all DSP functions.  There are NO front-end filters, the only bandwidth limitation comes from the tracking filter that is inherent in QSD operation.    A class D audio amplifier module is included and there is an oled display for normal use,   but the Pico also streams audio via USB, and can be controlled by CAT commands, so can be operated "headless" as well.  

I wanted to test the ability of the Pico Rx to demodulate weak signals on the longwave band,  and 630 meter WSPR provided the ideal target.   Few transmitting stations are able to muster more than 5 watts ERP due to the inefficiency of reasonable-sized antennas on this frequency.

My longwave receiving antenna is an active whip of the R.W. Burhans design that has proven to outperform all other antennas for LW beacon DX-ing.  It includes a low-pass filter that attenuates signals from the AM BC band and up.

The decoding software was WSPR-X. 

The test consisted of obtaining a 24 hour baseline using a SDR receiver with known good LW performance.  This receiver uses the ST Microelectronics STA-709 silicon radio chipset which was designed for car radio applications, including the longwave broadcast band,  and has a set of front-end filters and PC-based SDR software that sent data via VB-Cable to WSPR-X.

The Pico Rx was then connected to the same antenna without changing anything other than the audio source.   Using the USB streaming capability, I simply selected "Pico Rx" as the "microphone" device in WSPR-X.   A 12 hour run was deemed sufficient since only one semi-local signal can be heard during daylight hours. 

During its 24 hour test period,  the PC-based SDR received 12 different wspr beacons at distances up to 2416 km    In it's 12 hour test, the Pico Rx received 13 beacons, up to the same 2416 km distance.   The difference could be due to propagation,  the fact that not all beacons are in operation 24/7/365,  or other factors, but the bottom line is - the Pico Rx worked very well, spotting every beacon the more expensive and sophisticated receiver did.

The antenna no doubt played a major role as it provided the low-pass filter that is absent from the Pico Rx in this implementation.   An external filter would doubtless be helpful if the Pico Rx were used with a broadband antenna as undersampling of strong BC band stations would otherwise occur.