[Moon-Net] RFI from laptop via USB cable

James Morris jmorris at namei.org
Thu Apr 22 09:06:42 CEST 2021

Yep, I'm sure it's at IF.

I have an attenuator between the preamp and the transverter, which I'll 
try removing, thanks.

I'm finding it difficult to avoid driving the transverter rx path into 
saturation when measuring sun noise. I also have the rx gain pretty far 
down in the transverter (this is a Kuhne G4). I've spent quite some time 
experimenting with attenuators and rx gain to get the best dynamic range 

And I will also try directly connecting the audio.

James W7TXT

On Thu, 22 Apr 2021, Charles via Moon-net wrote:

> 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 masked.
> Another alternative might be to try to connect the 817 directly to the audio
> input of the PC.
> 73
> 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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James Morris
<jmorris at namei.org>

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