[Moon-Net] RFI from laptop via USB cable

James Morris jmorris at namei.org
Thu Apr 22 06:09:41 CEST 2021

I'm wondering if anyone has experience dealing with RFI from a laptop (or 
other computer) when connecting audio via USB?

I have a Kuhne 3cm transverter, an FT-817, and a Rigblaster (which uses a 
USB audio connection to my laptop). This has been working fine for 
terrestrial contacts, but I'm running into issues trying to receive the 
DL0SHF beacon.

When the USB cable is connected, there's a bunch of interference on ~144.0 
MHz, with sidebands extending up at least 25kHz, which makes a mess of the 
spectrum at the beacon frequency (144.025 at the IF radio, +/- doppler). 
I've tried adding ferrites to the USB cable but with no effect.

The laptop is a Thinkpad T470s which has otherwise worked fine with weak 
signals at higher frequencies in the band. This is running on batter 
power, also.

Any ideas / suggestions?

- James W7TXT 
James Morris
<jmorris at namei.org>

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