MAP65 and Quadrus SDR connected

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What is MAP65 and Quadrus SDR?

MAP65 is part of the WSJT software stack developed for weak signal reception by Joe Taylor K1JT .
MAP65 contains support for wideband receivers. In this context, wideband means 96 kHz IQ sampling, which can be implemented with a premium sound card.  If you have an RF to baseband conversion, like LinkRF, it is possible to use the digitized baseband IQ signal with a stereo sound card, and feed it into the MAP65 software. Thus, not only a single 3 kHz wide signal is processed. However, the MAP65 is ready to process and decode all of the signals that can be found in its full 90 kHz bandwidth.

Wideband IQ stream from the Quadrus SDR receiver platform

The SDR receiver software of the Quadrus SDR platform can also provide the wideband IQ signal stream on the audio interface, which is the simplest way to integrate the SDR receiver front-end with the MAP65 processing back-end. Some more info on IQ signal from the Quadrus SDR receiver can be found here:

Phase-coherent SDR receiver for dual polarization reception

Wideband processing is not the only feature of MAP65. It is also able to process two phase coherent parallel channels. This can be used to process a dual polarized antenna system, and exactly match the receiver polarization to the incoming wavefront polarization. 3 dB gain can be achieved this way compared to a simple adder circular antenna system. In case of weak signals, each dB is important.

On the other hand, what I originally liked to use it for, was tracking small satellites based on changes in their polarization. With stabilized satellites, we can deduce some additional information on the ionosphere based on the polarization change of the Faraday rotation. So, lot of promising experiments…

Connecting MAP65 Quadrus SDR with virtual audio cable

I simple used the setup window of the VAC software, and set the first channel to the maximum sampling frequency of 96 kHz.

vac vac ctrl

The SRM SDR software can send the audio samples only with a 48 kHz sampling rate. The 96 kHz sampling rate is not supported yet. As you can see in the picture, the noise floor ends at 48 kHz, because the signal is interpolated to 96 kHz, but there is no real signal above 48 kHz. The spectrum test pictures were generated with the internal generated feature of the SRM SDR receiver and tested with the SpectrumLab audio signal processing software.

48ksps 96ksps

So, finally I connected the SRM SDR receiver front-end output to the MAP65 digital signal processing back-end, and saw the same spectrum with the two test signal.

map65 map65b


The MAP65 wideband dual polarized receiver of the WSJT software stack was connected to the SRM SDR receiver front end of the Quadrus SDR receiver platform. The IQ signal stream connection was verified with internally generated test signals. I am waiting for the real antenna signal to test the real  signal processing capability.

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