Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

WReeve
 

Niceto - Thanks for looking at this problem. I previously reported USB noise in the spectrum at but received no reply.

I just spent 3 hours in my lab testing various USB cables and ferrite beads. For these tests I terminated the R2 receiver in 50 ohms to eliminate a noise path to the RF input. Most of my tests were with new Volutz USB cables, 1 m and 5 m long, and Fair-Rite clamp-on beads, 31 and 61 mix..

I confirmed what I had suspected before: The USBs and ferrite chokes have only a minor or negligible effect. Instead, the spyserver software or receiver is inconsistent. USB noise can be made to come and go simply by stopping and then starting SDR#.

See attached screenshots. For these, I simply started and stopped the spyserver using SDR# Connect/Disconnect button and Play/Stop button. I did not touch the physical setup in any way. And I could replicate the good and bad spectrum with any cable and any configuration of ferrite beads. In other words.the cable or ferrite chokes had nothing to do with it.

I found that I can almost always make the USB visible or invisible by pressing in order Connect, Play, Connect again (to disconnect) and then Play again, waiting a few seconds between each press. If the noise is there, repeat the sequence and the noise will be gone. Sometimes simply pressing Play, Stop, Play will do it.






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Whitham D. Reeve
Anchorage, Alaska USA
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