I have taken a couple of days to put together a closer look at an RXTX using the Tayloe detector design.
The PDF can be downloaded here TAYLOE DETECTOR
This QRP RXTX has not yet been implemented on an Arduino shield, it will be a tight squeeze, but I will attempt the PCB layout in the next few weeks. And if all goes well fabricate the design early next year.
The Low Pass Filter is already in production.