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There are many different ways to pair your radio’s audio and ptt circuits with a computer to work digital modes.  This is not a discussion of all the different ways.  This is how  I (AC9RZ) did it.  Most of the information is readily available if you search this list and online.

 I'm using an Easy Digi kit for switching PTT and isolating Rx audio.  I found the loss was too high on the Tx side so I'm going right from the sound card to the rig for Tx but I will describe using both sides of the Easy Digi below.

I set up my radios with a mono jack for the speaker and TRRS for mic/PTT and corresponding cables on the Easy Digi so everything is interchangeable.

I'm using a USB sound card and an FTDI cable.  I have the sound card and FTDI cable plugged into a small unpowered USB hub with the Easy Digi hot glued on top with the cables all hot glued for strain relief.  It is ugly as sin but sits out of sight and works.

  • Pop the cover off the USB sound card and desolder the two audio jacks.
  • Cut two pieces long enough to go from the sound card to the Easy Digi off the mono cable.  It is 6’ long, you have plenty to spare and it is good shielded cable.
  • Solder the cables where the jacks were and route them out the holes in the case where the jacks were.
  • Solder those cables to the corresponding spots on the Easy Digi.  Mic from the sound card to Audio to PC on the Easy Digi and speaker on the sound card to Audio from PC.
  • Solder the audio cable with plugs to the Easy Digi board.  
    • Audio to your radio’s speaker via the mono cable
    • Mic to your radio’s mic via the 4 conductor cable if doing it like I did.
    • The last connections are from the FTDI to the Easy Digi and the Easy Digi to your ptt.
  • Cut the RJ45 connector off the FTDI cable and connect the following cables to the Easy Digi (These are the only wires you will use in this cable):
    • Black to DIG GND
    • Green to DTR
    • Brown to RTS. 
  • Connect PTT HI on the Easy Digi to your PTT wire and PTT GND to your PTT ground.  Both of these are also part of the 4 conductor cable.  
  • Plug the FTDI cable and USB sound card in the USB hub and connect the hub to your computer.  

If you are using Windows, your machine should set both up without issue. 

  • Connect the mono jack to your radio's speaker jack and the TRRS plug to your TRRS jack or however you have your mic and ptt connected.
  • Assuming you are using WSJT-X, in settings under the radio tab select RTS for PTT method and whatever port the FTDI adapter cable shows up on.
  • With a dummy load connected to your radio click the Test PTT button several times to make sure it toggles Tx on and off on your radio.



One last very important thing.
The heat sinks on the IRF510’s are sized for casual voice and cw work not the full blast usage of digital modes.
Make sure you have a plan to deal with the heat.  There are many other posts on heat sink ideas.
I have found even a little air flow from a small fan makes a huge difference.

Parts List

 Easy Digi <-- Author Bought this (now sold) Easy Digi Kit

Easy Digi is sold by cliffordwareham on Ebay, Easy Digi page:

mono cable with plug

4 conductor cable with TRRS plug

TRRS jack


USB sound card

FTDI cable

(do not buy a cheap TTL adaptor, they do not put out high enough voltage for the opto coupler on the Easy Digi)


USB hub


TRRS Breakout Jack

I found this breakout jack helpful for confirming the wires on the 4 conductor cable before soldering up the TRRS jack 


Also worth noting, you could probably save on shipping to order your parts from less suppliers than I did.  This wasn't the top of my project list so I just kept adding parts on to orders for other things as I thought of it.


A good number of people working digital modes are contesting or working toward awards.  You would be doing them a favor to log your QSO's.  Logbook of The World (LoTW) is the most popular and it is free even to non ARRL members.




KC8VRI’s Easy-Digi Parts, Price & Source

(updated Apr 27, 2019)


"EASY DIGI” Sound Card Interface $7.95 eBay item# 323255997507

100x60x25mm Plastic Electronic Project Box $1.90 eBay item# 272590733575 (5 min)

(2) 3.5mm 1’ Male to 3.5mm Male Stereo Audio Cables $1.52 eBay item# 302826667716 (3 min)

(5) 3.5mm Female Stereo Panel Mount Jack $0.27 eBay item# 253947882510 (10 min)

CP2102 USB 2.0 to TTL UART Module $1.37 eBay item# 381374541932

(DTR and RTS were inverted, so don’t use the UART)

Top USB 2.0 to Serial RS-232 DB9 9 Pin Adapter Cable $2.30 eBay item# 113682859199

(DTR and RTS are high during transmit - this is what we want!)

D-Sub Connector 9 Pins Female $0.60 eBay item# 233184125667 (5 min)

(3) 3.5mm 3’ Male to Male Car Aux Auxiliary Cord $0.74 eBay item# 392038513285


Total cost ~$20 (including cables!), including shipping on most items.  The DB9 connector didn’t include connector screws and nuts, but I found suitable parts in my spare screw drawer.


Switching to the USB to Serial DB9 adapter allows most all software, i.e. fldigi, WSJT-X, Winlink; to work normally and you don’t have to invert the CTS and/or DTR signals from the computer.


The only add’l items I used was some Cat5 network cable for the serial connector (for PTT) and some electrical tape.  Be sure to use a stranded cable vs. solid wire.  The shorter foot long 3.5mm jack cables are for connecting from the Digi-Easy to the radio.  My uBitx used 3.5mm stereo jacks for headphone and mic jacks. Other radios may use larger ¼” jacks, or something completely different.


The Easy-Digi seller includes several pages of assembly and wire-up instructions.


For all the ⅛” jack connectors, I connected black wires (GND) to the longer jack lugs, and the signal to the “tip” lugs.  For “Radio Mic/PTT” I connected the Mic signal to the tip, and PTT to the middle conductor. Your radio may be different.


For the RS-232 DB9 connector, connect:

  • DTR to pin 4

  • GND to pin 5

  • RTS to pin 7


When I setup the fldigi software, I went to ConfigureRig ControlPTT Hardware and checked

Use separate serial port PTT, Use RTS, Use DTR.  Baud rate and stop bit are NOT used so don’t worry about setting this.  To avoid erroneous PTT, power up the radio AFTER fldigi is running.


I printed a 2”x3.5” label on my laser printer to label the device, jacks, and of course my call sign.  Finished product looks pretty good for a homebrew project.


Good luck!