FT8 with the (tr)uSDX

Can it FT8? Yes it can.

Update: PE1NNZ has introduced a beta feature which allows audio over USB. I’ve posted an article on the subject here.

DL2MAN posted a video with detailed instructions for setting up the (tr)uSDX for FT8 using WSJT-X. Since the (tr)uSDX supports CAT control through it’s USB connector and it has 3.5mm audio in and out jacks, you can use it with a PC for digital modes.

It should be noted that you will need to modify the patch cable for the PC speaker out to the microphone input on the (tr)uSDX. The modification is to disconnect the “tip” connection, leaving just the ring and sleeve connected.

PSK Reporter FT8 from New Jersey

The first test I ran was on 20, then 30, then 40 meters. When viewing the “spots” on GridTracker, I was heard by about a few dozen stations on each band, all of which were in the United States, with the exception of a station in Japan (11,272km), who heard me on 40 meters at -14dB. The output power on 40 meters was 581mW. I ran the (tr)uSDX on the 5 volt USB source.

Signal Noise from PC

I looked at the signal from the (tr)uSDX on an SDR and the signal looked a bit noisy right after keydown before WSJT-X began generating its FSK audio output, then some more noise after WSJT-X stopped the FSK and before the radio was un-keyed. Further, you can see a bit of “noise” across the roughly 3k bandwidth of the upper sideband output.

FT8 Waterfall on (tr)uSDX During Transmit Cycle

I’ve captured an audio recording of this “static” or noise before and after the transmit cycle, received by a nearby radio which had it’s RF input grounded. Note that there was no noise in the receiver once the transmission stopped. The receiving radio indicated an S9 for signal strength.

FT8 Transmission from (tr)uSDX

I noticed this same “static” noise to be present during the FSK transmission when the signal level from WSJT-X was too low, and raising it up to just the right spot the static was minimized. The noise rises to an audible level when there is little or no input level into the rig.

When disconnecting the 3.5mm plug from the microphone/key jack on the (tr)uSDX, the noise disappeared on transmit (when using the built-in mic). It appears the noise is related to the connection to the C-Media USB Audio device I am using. I will need to find a way to isolate that source of noise coming from the PC audio output. Perhaps a different sound card device would have better results. I did test the built in sound card in the desktop PC, and the noise was lower than the C-Media USB device.

Audio Isolation Transformer

I decided to try to eliminate the possibility of a ground loop or other source of interference by putting an audio isolation transformer inline between the audio input of the (tr)uSDX and the audio output of the PC.

Audio Isolation Transformer

Most of the noise was eliminated. Below is a recording of the FT8 transmission received by the FT-991A with this transformer inline.

Receiver Capability

The (tr)uSDX seemed to perform well receiving for FT8 decoding. I confirmed reception of stations on nearly the full channel bandwidth from the low end to upwards of 2,700 Hz. I ran the receiver test on 20-meters during the afternoon.


The (tr)uSDX appeared to work well for my first round of tests on FT8. Although the PC connection was a bit noisy, it did work, I managed to make a contact to test the setup. Not only did it work, it worked on the lower power output (powered from a 5 volt USB power source). All tests were run on an MFJ-2012 OCFD.

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