The RSPduo is the latest product from SDRplay, and it's main defining feature is it's dual RX channels. The two channels allow you to simultaneously listen to two stations that may be at opposite ends of the spectrum. Of course the same could be done cheaper with two separate RSP1A devices, however the advantage of the RSPduo is that the two channels are phase coherent. This opens up a lot of technical possibilities such as active noise cancelling/spatial filtering of an interfering signal or unwanted RF noise.
The basic idea behind phase coherent noise cancelling is that you have one antenna pointed towards your signal of interest, and the other pointing towards the interfering signal or coupled to the unwanted noise source. The unwanted signal/noise can then be subtracted from the signal of interest, resulting in a cleaner signal. This can only be done if the two channels are phase coherent like they are on the RSPduo.
Over on YouTube and his blog, ICAS Enterprises has been experimenting with noise cancelling on his RSPduo [Part 1] [Part 2]. The blog is entirely in Japanese, but all the relevant screenshots are in English, and we have provided Google Translated links. SDRplay have also provided a description of the process on their blog. The idea is to use Linrad to process the sound output of the two RSPduo channels from SDRuno. Linrad has capabilities that allow you to subtract two signals from one another.
In his experiments he receives a known 50 MHz CW beacon, and then injects an interfering test signal into the system. Then using Linrads 'signal adaption' feature he is able to completely remove the interference.
SDRplay have released a new product at this years Hamvention called the "RSPduo". The product uses the same technology as their previous RSP models, but this time includes a phase-coherent dual tuner architecture which allows you to tune to two completely separate 2 MHz bands of spectrum simultaneously. The RSPduo retails for US $279.95 + shipping. Their press release reads:
Today at the Dayton Hamvention, SDRplay is announcing the launch of a new Software Defined Radio product – the RSPduo.
The RSPduo is a radical new addition to the RSP line of SDR receivers from SDRplay. Architecturally, it is different from any previous RSP in that it features dual independent tuners, both piped through a single high-speed USB 2.0 interface.
The SDRplay RSPduo is a dual-tuner wideband full featured 14-bit SDR which covers the entire RF spectrum from 1kHz to 2GHz giving 10MHz of spectrum visibility. Initially using Windows based ‘SDRuno’ supplied by SDRplay, you can simultaneously monitor two completely separate 2MHz bands of spectrum anywhere between 1kHz and 2GHz.
Superficially the RSPduo looks identical to the highly popular RSP2pro and will be able to operate in a very similar way. However, it also allows a completely new and exciting set of usage scenarios such as:
1. Simultaneous monitoring of two widely spaced bands – e.g. 40m (HF) and 2m (VHF) 2. Mixing and matching applications simultaneously – e.g. ADS-B and ATC scanning 3. Phase and time coherent demodulation of two receivers
Scenario 3 is very difficult to achieve with two separate USB devices because of the uncertainty of USB latency. The RSPduo overcomes this limitation because all traffic goes through a single USB interface, thus enabling the possibility of the development of various types of diversity demodulation such as: spatial, frequency and polarisation which can bring huge benefits in terms of improved performance.
As well as adding a second independently controlled tuner, which in itself, offers a whole new set of exciting usage possibilities, the SDRduo features 14bit ADCs and a completely re-designed RF front end. These changes provide better RF selectivity and even more dynamic range, offering outstanding performance under extremely challenging reception conditions. The combination of performance and features makes the RSPduo our highest spec RSP yet and sets a new benchmark in the sub $300 SDR market.
Lots of great new videos are appearing on YouTube showing the Dual Tuner RSPduo in use. Just search for RSPduo in the YouTube Search bar.
While it appears that it will be a useful tool for multi-band monitoring, what we're looking forward to most are the phase coherent applications. Thanks to its phase coherence and predictable USB timing implementation, the unit should be very useful for passive radar and spatial filtering techniques, and we're hoping that SDRplay will be working on software for at least the latter. Multi-channel phase coherent applications are probably going to be one of the the next big developments in the SDR space so it's good to see low cost hardware with this potential coming out now.
We'll be reviewing the unit ourselves within the next month, so keep an eye out for that post!