Icom IC-705 QRM caused by USB CAT control

 Date: August 9, 2021

When using WSJT-X with my IC-705 connected by USB all bands (160m - 70cm) are drowning in a spike-like noise pattern that renders the entire device unuseable.

The setup to reproduce this is issue simple: LogPer or Dipole Antenna (placed at max possible distance) → 6m Hyperflex-7 cable → IC-705 (on battery) → 3m USB cable (Shielded/Ferrited) → PC (on battery)

Then start WSJT-X and have a close look the the waterfall. You will be able to see the structure of the USB frames on the HF spectrum.

This is kinda strange, as my shack (Lots of different SDRs, etc.) never had any USB noise issues at all. I’m well aware of this kind of problems.

Attempts of getting rid of this issue

Tests regarding USB
  • The USB cable had no shielding at all. I replaced it with a high-quality cable from HAMA.
  • Added 15 loops of the USB cable around a FT240-32 /-43 ferrite ring
  • Added a USB isolator (ADuM). Didn’t work at all.
Tests regarding my shack infrastructure
  • Replaced all antenna cable connectors
  • Checked ground
  • Tested it with different PCs (RasPi on Battery, etc.)
  • Running everything on battery (standard in my shack)
Tests regarding my antenna
  • Using a directional antenna. Nope. Effects still visible in all directions.
  • Moving my PC away from the receiver. Nope.

Attempts of getting rid of this issue

There is still a lot of USB QRM left. I’m not happy with the results. The IC705 seems to have problems with the USB signal created by my Acer Swift 1 notebook. There are several reports from reddit hat they have seen similar behavior with some notebooks. It doesn’t seem to be a generic behavior of the device.

For now my solution is to remote control the entire device using WLAN. The application will create virtual audio and COM interfaces.


12/2020: My dealer was able to reproduce this issue with a second IC-705 on his test site

12/2020: Had two very long calls with an Icom engineer. They assume that thist might be a radiation issue from my cable and/or PC.

12/2020: Ordered a PreciseRF Magloop to deal with my limited antenna space. This will give me a new chance to re-check this issue with an entirely different kind of antenna.

02/2021: Same problems using a MagLoop.

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