Interesting thing happened today.
One of the symptoms of RF in the shack is when you’re using a digital mode like FT8 and you transmit, your computer says that the audio input has gone away. This has happened to me on Linux, Windows, and MacOS on their own respective machines.
Well today, I was adjusting my EFHW wire into an inverted V because of bad SWR. I have a 6ft counterpoise attached to my transformer and I thought this was leading to an extra dip around 12 mhz.
Well just for giggles, after I made a contact on FT8 on 20 meters, I removed the counterpoise and tried again.
BAM! Audio disconnected!
This was just data point but it makes sense since the purpose of the counterpoise is to provide a low impedance (lower than the surface of the coax) for common mode to exit/balance or provide “something to push against on transmit.
Note that I only use the same (probably cheap, unshielded) USB cable to connect to my Raspberry Pi, MacBook, and Surface. 5 wraps of the USB cable on a ft 240-43 toroid “cures” the problem (not really, the RFI is still coming back on the coax).
15 minutes after this post….
I went outside and removed the 6 foot counterpoise and tried to re-transmit on 20 meters ft-4. Bam. Audio went out. You can see just seconds ago I had a QSO with N7JB when the counterpoise was on. Hang on while I go connect it back and then try to transmit again..
HOLY WOW!
I put the counterpoise back on and transmitted on 20 meters ft4 and look what the cat dragged in! KL7TC – the coveted state of Alaska – on 5 watts on my ICom 705! 2,500 miles. I mean, I can get about 1,000 miles on 1 watt going to the east and west coasts of USA so it shouldn’t come as a shocker that 5 watts can reach 2,500 miles but Alaska has been hard for me to QSO with.
So there you go – if you’re losing your USBaudio connection on Tx, consider fixing the RFI problem rather than reaching for a ferrite to wrap your USB cable in (if you have 100% control of all other factors).
Note2: Today’s experiments (and cure with the FT 240-43) were on 5 watts. My previous issues with my 705 have been on 10 watts with a mag loop that’s an arm’s length away with me and the radio sitting in the null region.
73,
ae0rs
