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RSPduo Dual Channel SDR – A Hit at Dayton 2018

sdrduo dual channel sdr

In case you missed it, SDRPlay hit a home run at the Dayton Hamvention last week with the introduction of the new RSPduo dual channel SDR. Let’s take a look. 

It’s amazing how much SDRPlay Limited has accomplished since it was incorporated four years ago this month. By leveraging the Mirics investment in the MSi3101 chipset, SDRPlay has stormed across the radio community with a series of wonderful, low-cost DC-to-daylight receivers.

As you know, I have been advocating Spatial Interference Filtering Techniques which would benefit from low-cost dual channel SDR receivers. Obviously SDRPlay has been developing the RSPduo long before my articles were published. But the timing is great and a big thank you. At under US$300, the RSPduo definitely advances current state of the art!

The RSPduo should provide coherent two-channel reception across 100 kHz to 2 GHz. Sampling bandwidth are available from 200 kHz to 1.5 MHz. Both receivers share a common clock. The second receiver is another MSi001tuner. Both data streams come out of a single USB port.

SDRUno software supports two channels right now, but no diversity reception yet. Expect to see diversity and phasing in the upcoming version 1.4. SDRPlay also promised that the new API will soon be made available to third-party developers.

Here are some RSPduo technical details and a video presentation about this new receiver.

RSPduo Dual Channel SDR – How SDRPlay gets 14 bits out of the ADC

Up until now, most people considered the SDRPlay products to be a 12 bit solution. So, when implementing the RSPduo dual channel SDR, how did the designers accomplish 14 bits from the same hardware? Here’s the story.

Mirics brought their MSi3101 chipset to market in 2010 to provide a broadcast television and radio reception solution in Europe. For a while, they even released a (short lived) USB Dongle in 2013. Although the system was proprietary, hackers in the Linux community started experimenting with new drivers to unlock the potential.

If you follow the trails, you will find that the hackers discovered that the MSi2500 has several different modes of operation, depending on how it is configured. It is capable of producing 8, 12, and 14 bit complex signed data performance. Even 16 bit unsigned. Different data streaming rates exist, ranging from 17.2 Msps with 8 bits to 8.6 Msps with 14 bits.

So, by reducing the sampled bandwidth down to 1.5 MHz per channel, the RSPduo dual channel SDR is able to work in Low IF mode at 14 bits.

The magic comes from the use of continuous time multi-bit sigma-delta ADC in the MSi2500. You can adjust the sample and data rates, as well as filtering and decimation in ∑Δ analog-to-digital conversion. If you are interested, watch this Hackaday video about how sigma-delta devices work.

Looks like I will soon sell my RSP2 and get the RSPduo.

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