Re: rough draft of how to connect BITX to PC for digital modes wiki

Joe Puma

Sounds like a good setup. I’ll be doing something similar. 

On May 17, 2018, at 9:08 PM, atouk <atouk@...> wrote:

I followed a similar approach.  Mounted a 4 port usb hub inside the case.  One port for the radiuno, one for a 6 buck usb sound dongle, two free for future use (rtl dongle for panadapter and maybe a pi0 for for something in the future).

I also used an Easy-Digi board simply because I prefer to have the radio as electrically isolated from the computer as possible.  The advantage of the USB sound dongle is that the radio gets it's own dedicated audio in and out channels. This way I can have WSJT-X running and not lose my main PC audio.   Disadvantage?  I used an unpowered hub that puts a load on a single USB port with the RTL dongle plugged in.  I'll change that later.

The only thing I had to do to tame the audio is to put a 330 ohm resistor across the output side of the audio out (dongle mic in) to make the volume adjustment smoother.

I run the CEC software to control freq changes and transmit from WSJT-X via CAT control through Onmi-Rig.

On 5/17/2018 8:45 PM, Doug W wrote:
It seems almost every day (or hour) someone has a question about connecting their radio for digital modes.  Following are my cobbled together notes that if the group deems worthy could be the start of a wiki page on the topic.  My concern is my use of a TRRS jack might be too specific, but at least this is a place to start.  Your feedback is welcome.


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 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.  There are links below to all the parts I used.

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.  Now 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.  Now solder the audio cable with plugs to the Easy Digi board.  Audio to your radio’s speaker via the mono cable and 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, Black to DIG GND, Green to DTR and Brown to RTS.  Those are the only wires you will use in that cable.  Now 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.  Now 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.

Following are the parts I used:


Easy Digi

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

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


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