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Incoherent spikes in direct sampling mode.

Posted: Thu May 06, 2021 4:24 am
by FEuBZD4h5endBsjl3Dbv
I've been attempting to run the dongle in direct sampling mode so I could pick up some AM stations. Whenever I attempt to use the modes, I see nothing but incoherent signal spikes that do not move (q branch) or move randomly as I change the spectral window (I branch).
Screenshot 2021-05-06 000745.png
Q mode. Spikes are present throughout the MF and HF bands
Screenshot 2021-05-06 000745.png (2.04 MiB) Viewed 538 times

Re: Incoherent spikes in direct sampling mode.

Posted: Mon May 10, 2021 12:19 am
by hotpaw2
Those could be noise spikes caused by harmonics from a nearby 100 kHz power supply or other noise generator (solar panels, LED lights, USB chargers, etc.). Try running your RTL-SDR from a portable laptop/notebook computer on a picnic table far (1000's of meters) away from the nearest buildings, solar panels, or power lines.

The spikes could also be intermodulation overload distortion from a really strong nearby station. Try a much smaller antenna, or even no antenna. If the intermod spikes go away, then you my need to add a broadcast blocking filter (or two), a bandpass filter, or an attenuator.