Hi Jose, am I right in thinking you want to use sdr# with the tetra plugin and your sdrplay rsp1a to decode tetra?
Somebody will correct me if I’m wrong but I think sdr# software will not work with the rsp1a. However all is not lost there is a workaround. Although it is a bit long winded. It can be done through audio piping, basically you need vbcable (virtual audio cable) to pipe the Raw iq data stream from sdruno (iq out ) to sdr#/source: ( iq from sound card ) then there are more settings to change I said it was long winded.
1 Download the latest SDR#
2 Download the EXT/IO add on from here SDR#_ExtIO_v1.1.zip http://www.meteorgis.space/files/ExtIO/
3 Extract both zips into a new folder (SDR# and the EXT/IO add on.
4 Place your RSP1a EXT/IO dll file into your newly created folder.
Follow the read me inside the SDR#_ExtIO_v1.1.zip file.