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Dual Antenna Spatial Filtering Really Works

dual antenna spatial filtering

If you are lucky enough to have two (or more) antennas, you can get started with dual antenna spatial filtering using RSPduo. Look and listen.

Right now, I have three antennas set up in my back yard. Two are on the tower – an HF beam and a 40 meter dipole. My third antenna, a switched pair of orthogonal wideband loops, is near the ground. You can see these in the picture above.

While separation between loop and beam is only around 70 feet, that’s enough to experiment with signal time of arrival differences to do some really basic beamforming.

My first experiment is focused on spatial interference filtering to reduce RFI from my neighbor’s halogen lights, about 100 meters away. Her whole house is one big RF interference radiator which tends to wipe out reception on 11 MHz (25 meter) short wave broadcast band. While I can reduce this noise with my ANC-4, digital beamforming with a coherent SDR is a lot more fun.

Here we go with two videos of RSPduo diversity reception to reduce noise:

You can see the filtering reducing noise and bringing two stations to life: China Radio International on 11,910 kHz and All India Radio on 11,560 kHz. Both of these signals traveled a long ionospheric path to Calgary only to get clobbered by the halogen lights next door. With the RSPduo, dual antenna spatial filtering knocks down the noise really well.

Dual Antenna Spatial Filtering with SDRuno

I find the SDRuno software challenging to use but powerful. Out of the box, hooking up my HF beam to one RSPduo tuner and the wideband loop to the second channel worked fine, as shown in the videos.

Two issues, though. First, the Diversity Window is quite small and adjusting amplitude and phase is quite finicky. Reducing the mouse cursor speed on your PC might help – see the mouse Settings in Windows 10. Adding the ability for me to expand this Diversity Window would make tuning a lot easier.

Second, we would benefit from having the Spectrum Window synchronize to stay at the same Zoom factor each time you switch between Single Tuner versus Diversity modes. That’s a suggestion I would make to SDRplay.

But these are pretty small nits I am picking. Overall, well done SDRplay folks.

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