Multi-channel SDR receiver audio connections

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What is multi-channel SDR receiver audio?

The Quadrus SDR receiver platform consists of the DRU-244A SDR hardware digitizer and the SRM-3000 SDR software receiver. Both the hardware and the software are multi-channel capable. The hardware is able to digitize 40 MHz instantaneous (Nyquist) bandwidth with its 80 MSPS Analog-to-Digital Converter (ADC). Within this bandwidth narrower bands may be selected using built-in digital tuners or Digital Down Converters (DDC). The DDCs are implemented with dedicated applications-specific chips on the hardware. Each chip contains four channels, and up to four chips may be installed on one card. So, the card’s maximum number of channels is 16.

DRU-244A-1-1-PCI DRU-244A-1-4-PCI

The SRM receiver software can handle each of these channels, and provides receiver functionality – including independent setup and display windows – for them. Each channel can deliver its own demodulated audio output.

srm-2 srm-1

Audio connection for multi-channel SDR receiver systems

Integrated systems can be easily built at a higher level using the audio connections of the multi-channel SDR receiver. Besides audio connections, it is possible to use the API of the DRU-244A hardware or the API of the SRM-3000 receiver as well. Both of them are available from the support page:

Selecting audio output for the receiver channels

The SRM-3000 SDR receiver software has the capability to select the output audio driver for each radio receiver channels. If you have some audio card or virtual audio cables installed on your machine, you can redirect each radio channel to different audio outputs. I had four virtual audio cables installed on my machine during my tests.

vac ctrl

I could easily select the output and input – including the real sound card channels and the installed virtual audio cables alike – in the SRM-3000 SDR receiver software and in other software packages as well, like the Spectrumlab.

out channels selection out channels selection 2

Additional info on using virtual audio cables with Quadrus SDR receiver platform can be found in my earlier posts:

Testing the multi-channel SDR receiver audio connections

I used the well-known Spectrumlab software for testing purposes. I configured the SRM-3000 SDR receiver to be in the standard internal generator mode. All of the four available channels were tuned to the same frequency, but the demodulator offsets were different as follows: 500/800/1000/1200 Hz. Thus each channel generated a different audio output frequency at its USB/SSB demodulator. This can be seen on the screenshots below.

out channels 2a

Spectrumlab is not prepared to handle multiple channels, however, it is possible to run multiple instances of the software, and set them up with different inputs. Usually, signal processing at this scale requires large amounts of memory and a lot of processing power, so a high-power machine is needed.

Additional multi-channel SDR receiver audio connections to decoders

Besides Spectrumlab, I have also tested some of the well-known decoder software packages, like Code300 and MultiPSK. I’ve managed to receive some RTTY and CW stations around 10 MHz, and was able to decode the output of the radio channels with the signal processing software.

rtty02 rtty01

cw01 cw02


The Quadrus SDR receiver platform has multi-channel reception capability. Up to 16 channels can be received and demodulated with a single instance of the DRU-244A SDR digitizer and the SRM-3000 SDR receiver software. External software packages may be employed to further process, demodulate, and decode digital waveforms. The easy way to connect the multi-channel SDR receiver platform with multiple instances of the decoder software is by using virtual audio cables connections. The connections and the decoding capability were proven with Spectrumlab, Code300, and MultiPSK software packages.

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