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


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.

Whitham D. Reeve
Anchorage, Alaska USA

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