Clicking-type noise on transmit audio on FT8
VK4ADC > 28-06-2021, 02:34 PM
I have just replaced the shack PC - which of course has different ports to the original machine. This necessitated adding another 4-port USB hub that has the USB/serial interface to feed CIV to the Icom transceiver, a USB/audio sound card device (ie FT8 audio in/out) and the USB/serial connection for my rotator control device, all connected to it.
The WSJT-X software worked with the USB sound interface, my transceiver was keyed by VOX, frequency was software controlled, and I still wasn't getting QSOs stacking up as quickly as before the hardware changeover.
Fortunately my IC-7400 has an audio monitor button active on transmit and that was a great revealer : there were random audible clicks affecting the transmit audio quality.
First step was to replace the USB sound card interface device - different audio levels but click sounds still there.
Plugging the USB interface device into a different (and powered) hub just in case the original total current draw was too high : no, still clicking sounds on the TX audio.
Found a short USB male/female extension lead so the USB sound device could plug directly into a USB port on the front of the PC (extra cable length needed) : NO CLICKING sound.
No real explanation as to why it only happened on a USB hub - powered or unpowered - but there is a lesson here. If you are re-configuring your station for digital modes , or replacing the shack PC/laptop, then have a listen to your transmit audio (eg using the Tune button in WSJT-X) and check for extraneous noises on a suitably-tuned receiver. It could save you a bit of time, and maybe heartache, because it "isn't working like it's supposed to".
The fix : Connect the USB / sound interface directly to the computer's USB port and then put other peripheral devices on the hub(/s).