[Moon-Net] RFI from laptop via USB cable

Charles g3wdg at moon-net.eu
Thu Apr 22 08:41:37 CEST 2021

Hi James

It sounds like the QRM is coming in at the IF.  Do you have any 
attenuation in circuit between the transverter and the 817?  If so, I 
would take it out so that the noise from the transverter (and preamp if 
you have one) might be at a higher level so the QRM is then sufficiently 

Another alternative might be to try to connect the 817 directly to the 
audio input of the PC.


Charlie G3WDG

On 22/04/2021 06:09, James Morris via Moon-net wrote:
> 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

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