NUD X1M PSK31 Project

The digital mode of PSK31 is a natural fit for a QRP rig like the X1M.  A quick Internet search resulted in finding G4ILO's USBlink website where he used a USB-based soundcard along with KH6TY's PPT circuit to create a simple PSK31 interface.  I ordered up a USB soundcard interface from Amazon for less than $5, dug through my junk box for parts, and modified G4ILO's circuit to work with the X1M (using fixed values of resistors for a no-adustment-needed circuit).

The schematic (click on the image for a larger view) shows the simplicity of the circuit.

The output from the X1M's headphone jack is attenuated by R1 and R2 and then capacitively fed to the USB soundcard's "mic" input.

The output from the USB soundcard's "spk" output is capacitivey coupled to the X1M "mic" input through C2 and attenuated by R4 and R5.

The push-to-talk (PPT) circuit consists of an amplifier (Q1), voltage doubler/rectifier (C4, D1, D2, and C5), and switch (Q3 and D3).  Transistor Q2 drives the red LED D4 whenever the soundcard is sending a signal.

I began construction by removing the USB soundcard circuit board from the plastic housing, an easy task since no glue is used to hold the housing together.  I then soldered wires to the 5 volt and ground pins on the USB connector (as with all of the images, click on the image for a larger copy).
Flipping the USB soundcard board over, I soldered wires to the “mic” input (blue wires) and “spk” output (green wires).  The solid color wires are the signals, the wires with the white tracer are the ground wires.  I also removed the green and red LEDs from the circuit board (to be used as the power and PPT LEDs).
I used some black electrical tape to insulate the bottom of the USB soundcard…
…and installed the USB circuit board in an empty ALTOIDS tin, keeping the board in place with hot-melt glue.  I installed the LEDs in the other end of the ALTOIDS tin, again keeping the parts in place with hot-melt glue.
I built the circuit itself on some perf board, using point-to-point wiring, soldering the connections as I went.  As with the USB circuit board, I insulated the bottom of the perf board from the ALTOIDS tin by using black electrical tape.  I passed the headphone and mic cable ends through a grommet.
Works like a champ using Digital Master 780 with the USB soundcard mic level set to 30.