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Digital Versus Analog SIFT

digital versus analog sift

Which reduces wideband RFI better: digital versus analog SIFT. Take a look at my experiment and judge for yourself.

As you know, I am a huge fan of using Spatial Interference Filtering Techniques to reduce local RFI. As the next generation in interference fighting, SIFT works by manipulating amplitude and phase of competing signals and noise. You can apply digital SIFT within a two-channel SDR receiver. Or, you can use analog SIFT with an outboard phasing box and two antennas.

People ask me if there is any advantage to digital beamforming with diversity reception in a two channel coherent SDR. Can’t you achieve the same effect with an analog device like the ANC-4, MFJ-1026 or NCC-1?

Short answer is yes, both work, and pretty well. Digital beamforming gives you more precise control over the phase and amplitude of each channel at baseband. But, to do this, you need two things. First, a two channel coherent receiver, like the RSPduo. Second, software that conducts the beamforming such as the SDRuno or PowerSDR.

On the analog side, all of the QRM Eliminator devices let you do beamforming (subtraction of competing signals and noise) ahead of the receiver. All of these do noise reduction, and the better ones like the NCC-1 give you enough control to create phased arrays with two antennas.

So, is there a best approach?

Digital Versus Analog SIFT Experiment

You can see the results of my digital versus analog SIFT experiment. My receiver was the RSPduo, running in either single or diversity mode. My main antenna is an HF beam on a 50 tower. My auxiliary antenna was a vertical dipole (E-Field) probe at close to ground level. At the top of the picture is the raw noise and signals in the 25 meter band single channel with the beam on the tower going into Tuner 1 of the RSPduo. Really bad wideband RFI.

In the middle is the result of digital beamforming with diversity reception on Tuners 1 and 2. At the bottom is the result of analog phasing with the DX Engineering NCC-1 ahead of Tuner 1.

Results? Both worked well. My NCC-1 lowered the noise more but also attenuated signals more. Best SNR improvement came from diversity reception in the RSPduo.

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