VS: [WSJTX] WUB WUB WUB sound and drop-outs, but only at 20m #FT8 #txaudio #signalink

Reino Talarmo

Hi Christian,

You described very well a typical RFI situation. As you don’t have any problems at 20 m using no PC. then most probable ingress point is connection cables between PC and Signalink or Signalink and rig or both. (Actually in most cases so called Pin 1 problem). Typical fix is to add suitable ferrite common mode chokes on those lines. Easy way is to put wires multiple times through a ferrite toroid, if the connector fits through the ferrite. Also clip-on ferrites may help especially, if you can fit multiple turns through those. Another additional help is to connect grounds of  rig, Signalink and PC together with a heavy wire or wide strip thogether, it may be enough alone as well.

73, Reino OH3mA


Lähettäjä: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] Puolesta Christian Sandvig
Lähetetty: 11 April 2021 01:59
Vastaanottaja: main@WSJTX.groups.io
Aihe: [WSJTX] WUB WUB WUB sound and drop-outs, but only at 20m #FT8 #signalink #txaudio


Hi, I'm a new ham and I wondered if anyone can help me figure out a WSJTX/FT8 problem I am having. I've tried searching for the answer but I am so new at this that I think I don't know the right keywords to describe the issue.

I have a laptop connected to a SignaLink USB, to an Icom M802 (150W max), Ameritron SWR/Wattmeter, then a 1:1 balun, then an Icom AT-140 antenna tuner, and a ~34ft random wire antenna with a ~34ft counterpoise.

When I try to transmit FT8 at 30m and up everything works fine and I am able to make contacts. The wattmeter is showing 6-10W forward power depending on how I set the TX dial of the SignaLink. However when I transmit FT8 at 20m usually no one responds. I noticed some weird fluctuations on the wattmeter like a rhythmic movement and forward power periodically drops to zero. This does not happen at other frequencies.

To diagnose this problem I have used an SDRplay RSP1A connected to a front end isolator and a long piece of wire. I am also running RCForb and I can monitor my own signal from a generous Ham who has an open access rig in my town.  When I monitor myself broadcasting FT8 at 20m I hear a sound that seems like a deep-voiced man saying "WUB WUB WUB WUB WUB WUB" over my signal. If I turn the TX dial on the SignaLink down all the way this improves but it never goes away. 

In addition, during an FT8 transmission there are 1-2 periodic drops when it seems like my signal cuts out entirely, sort of like when your hand slips off of the PTT button for a second and you press it again.  However, the SignaLink PTT light remains on the whole time and the Icom "TX" indicator remains on the whole time. The wattmeter does drop to zero during the drop-outs. So I am wondering if the WSJTX software is producing these drop-outs somehow by sending the PTT signal but briefly not sending any sound?  Again I am only seeing this on 20m.

I can transmit directly from the radio (no computer) on 20m or any band using my voice and I do not see these problems. 

I have carefully followed the setup instructions for all of the software and for the SignaLink (to set levels, etc.) if that helps. I'm not sure what to try now!  Any ideas?

Here is a screenshot of the SDRuno waterfall showing a problem transmission. I think the wavy waterfall is the man saying WUB WUB WUB and I marked the 2 drop-outs with arrows.  

Really hoping someone can help!
(brand new ham)