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Digital Phasing Reduces Radio Frequency Interference

digital phasing

Watch digital phasing reduce local noise and interference using Spatial Interference Filtering Techniques. It really works! 

Here is a video demonstration of digital phasing to reduce neighborhood RFI on shortwave. I can dim the interference from my neighbor’s halogen lights by 10-15 dB and get rid of the annoying 120 Hz buzz.

Earlier this year, I wrote about Spatial Interference Filtering. Since spring, I have been experimenting with my Afedri AFE822x receiver from Israel. This radio listens to two channels on two antennas at the same time. The data stream is synchronized across both channels, making coherent reception a reality.

While I could use this for diversity reception, my main interest is noise or interference reduction. At present, my main antenna is on channel 1 and my noise probe is connected to channel 2. By mixing these two signals together and adjusting their amplitude and phase, I can do a pretty good job of subtracting the interference.

In the video, you can see me applying spatial filtering across a wide chunk of the 25 meter SWBC band. Using the phasing control, you can peak the interference reduction on specific frequencies. Good quality signals jump out of the noise.

Digital Phasing – Beamforming using the I/Q stream

You can do your own beamforming with the combination Afedri AFE822x and PowerSDR mRX software. These work together seamlessly. Synchronized blocks of I/Q data from the AFE822x arrive over a LAN connection. PowerSDR lets you use a phasing control to do some math on the amplitude and phase of the received signals. So far, this is the lowest-cost, high performance dual channel digital phasing solution I have found. The radio costs US $359; the software is open source.

Other software that does digital phasing with this SDR includes Linrad and SdrDx. Also, the new SDRPlay RSPduo is said to have coherent reception but we are still waiting for the software to accomplish this.I hope it arrives soon.

Soon, I will demonstrate how well digital phasing works compared to analog phasing using the ANC4.


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