MAP65 Quadrus SDR connection

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Setting up MAP65 Quadrus SDR connection with virtual audio cables

In order to implement the MAP65 – Quadrus SDR connection, the output audio stream of the channel should be routed to the installed virtual audio devices in Windows. In case you have virtual audio cables installed, it is possible to select one for each channel as you can see it in the picture below.


The standard, speaker output device is used to monitor the channels in this example. The four channels of the receiver are connected to four different virtual audio cables.
We have to select one other virtual audio cable – like VAC line 5 in our example – in the MAP65 software. Finally, the streaming software can be started to connect the receiver and the decoder software.

inp   stream

MAP65 Quadrus SDR connection testing

We can find a strong signal in the receiver window, and the same signal will appear through the virtual cable in the MAP65 wideband spectrum display too.


Please note that the output sample rate of the SRM SDR receiver is only 48 kHz, but the input sample rate of the MAP65 is 96KHz. The VAC software makes the interpolation between the two different sample rates. Thus, the inner +/- 24 kHz part of the MAP65 display will contain valid spectrum components.  The interpolation is done without any filtering, so we will see the image spectrum beyond the 24 kHz limit. If we set up a 15 kHz filter in the SRM SDR receiver, we can see the noise level in the spectrum accordingly and mirrored to 24 kHz as well.


In the picture above, you can see the signals from the generators which was set +/- 4 kHz around the nominal frequency. As you can see, the signal was positioned beyond and below the center using the IQ streams from the receiver. The same kind of signal tuning can be seen in the screen recording below.



Successful MAP65 – Quadrus SDR connection via virtual audio cables was proven using the IQ demodulator of the SRM SDR software. Virtual audio cables were used during the test, and the streaming software of the VAC package was employed for connection and to implement re-sampling between the different audio sampling rates of the two software.

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Multi-channel SDR production system

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Mult-channel SDR receiver

I’ve already published some posts on the multi-channel decoder capability of the Quadrus SDR fairly recently. However, I ended up doing some new tests with the MULTIPSK decoder, because some questions were raised.
As we’ve described it already, the DRU-244A based Quadrus SDR platform has multi-channel capability. It can be used to deliver up to 16 channels to the decoder system. Thus, it can be used very well in a production environment too.

MULTIPSK decoder software

This software stack was developed and is maintained by Patrick, F6CTE, and can be used to run different digital modes in the RF bands. In the SWL and UDX operation modes, we can use its receiver decoder capability. It contains a lot of HAM radio and professional digital modes, as you can see below.


Some of them are available in the free version, and some of the professional functionality is only available in the licensed version, which has a reasonable price.

Connecting Quadrus multi-channel SDR and MULTIPSK decoders

The easiest and most convenient way to build a multi-channel SDR production system is by using virtual audio cables (VACs) to connect the audio output of the Quadrus multi-channel SDR to the decoder software. In case we’d like to use the full capacity of the receiver, we need some cables and some instance of the decoder running on the computer. To do that I just needed to understand the audio settings of the decoder software. After a short email exchange with Patrick, I understood that the MULTIPSK stores the audio and other settings in config files located in the program folder of the application. So, I just needed to make four different copies of the program in four different folders, and set up the audio input to the different VACs accordingly. I’ve made shortcuts on my desktop too. I assigned the VAC 1..4 to the four channels of my receiver, and I used the same set up with the decoder too.


Testing multi-channel SDR production system

I tuned to the different frequencies – used by meteo stations from Hamburg – as follows: DDK2 4583 kHz, DDH7 7646 kHz, DDK9 10100.8 kHz.,templateId=raw,property=publicationFile.pdf/Schedule_rtty_01.pdf
Then I tuned the fourth channel to the 20 m amateur band. As you can see from the receiver screen, the reception in the late morning time is pretty poor at 4.5 MHz, however, the upper bands have strong signals. At the output screen of the decoder, we can see the meteo messages and the ham radio calls in the 20 m band.




If your decoder software has the capability to run multiple instances at the same time on the same computer, you can integrate a very powerful multi-channel SDR production system. The connections between the receiver and the different decoder software can be implemented as virtual audio cables.

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Multi-channel SDR decoder

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What is a Multi-channel SDR decoder receiver?

As I’ve described in my earlier posts, the DRU-244A SDR digitizer hardware contains up 16 radio channels as hardware Digital Down Converters (DDCs). These can be distributed in 4 channel blocks between different antenna inputs. One signal processor contains 4 channels and supports one input, which presents a limitation when pairing antenna inputs and receiver channels.

Integrating the multi-channel SDR receiver with external decoder software

There are several ways to integrate the DRU-244A based Quadrus SDR platform with external software packages.

  • direct programming of the DRU-244A SDR hardware employing its API
  • programming the SRM-3000 SDR software using its API
  • and simple audio connection with virtual audio cables

All the API descriptions can be found in the documentations of the muti-channel SDR hardware and SDR software. They can be downloaded from the support page on the Quadrus SDR site:
The first two methods requires some programming, however, the third one does not. It is very similar to connecting  your old hardware receiver to a decoder software. But in this case, the receiver itself is a software too. So, we just need a virtual audio cable.

Setting up the audio outputs

In the options menu you can assign an audio out device for all of the SDR receiver channels. Also, you can select the monitor sound device as well.

audio settings2

If you start each channel, the sound output of the demodulator will be routed to the selected audio device. It will be a mono channel in case of CW/AM/FM/USB/LSB demodulation, and stereo in case of IQ demodulation.
The monitor channel is usually employed to monitor the given channel, and has the audio routed to the loud speakers or head phones connected to your machine. If you touch one of the controls of a given channel or press the Monitor button, the channel will be automatically monitored, and you will hear its demodulator output.

Testing multi-channel SDR decoders

After setting up the system with different virtual audio cables, I’ve tested it with some well-known digital decoders, like MultiPSK, MMVari, Digipan. All of the multi-channel SDR decoders worked fine without any problem. Even several copies can be run on different channels and operating modes depending on the available computer resources.

mpsk01 mmvari02 psk31a


It is possible to connect the audio output of each channel of the multi-channel SDR decoder to an external software with virtual audio cables. It was proven to work with several digital post-pocessors, like MultiPSK, MMVari, and Digipan.

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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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Multi channel SDR receiver in a single PC

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While the DRU platform offers up to 16 channels to be addressed via a single DRU card, there may be applications, which need further channels. When building a multi channel SDR receiver system, users would like to avoid using multiple PCs – to keep costs down and simplify signal processing.

We have tested a setup consisting of 2 DRU cards in a single PC, and using the SRM platform: according to our expectations, everything went well – the software instances recognized the cards without any issues. The attached screenshot shows the cards under different physical addresses and device IDs.

2DRUs in one system dev9-dev4

This enables the user to build a system using our DRU platform that is able to listen to up to 80 channels in a single PC. Of course, for that you’ll need an appropriate motherboard, such as the ASUS P8B-C/4L, but for 48 channels you may find commonplace commercial solutions, such as the MSI H81-P33 or the ASUS H81-PLUS, to work as well.

Happy listening :-)

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Receiving Moon bounce signals

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What is Moon bounce?

Moon bounce is a form of radio communication with an Earth-Moon-Earth path, which is why it is also called EME communication. The first proposal to employ the Moon surface as a passive reflector for radio communications was made as early as 1940. A couple years had to go by before practical Moon bounce implementations could be proven.

The first practical proof-of-concept was project Diana performed by the US Army Signal corps on January 10, 1946. However, I can proudly say that our researcher were not far behind. Led by Zoltan Bay, they were also able to successfully perform their Moon radar experiment. Their first successfully received echo dates February 6, 1946.
Find the original publications here: Zoltan Bay Moonradar.pdf Radar-Echoes-from-the-Moon.pdf


The topic is well described in the history of NASA too: These experiments were crucial for satellite-based telecommunications and radio astronomy as well.

Bay and his team used very interesting device for integration:

What is the challenge in EME connection?

As with all types of the radio communication, the minimal requirement is that the transmitted signal should be received with sufficient Signal-to-Noise Ratio (SNR) so that the message can be demodulated and decoded. The necessary power level depends on the message and the format, and can be very different for analog (e.g., SSB), simple digital (e.g., CW Morse coded), and well-designed digital waveforms (e.g., JT65).

However, all of them should overcome the distance to the Moon and back, which includes the Moon surface scattering. Signal attenuation depends very much on the employed frequency, but we can safely say that for practical frequency ranges the attenuation due to path loss is around 270-290 dB. A pretty high value, isn’t it?

How to overcome path loss?

First of all, you need a lot of power and a big antenna. Usually, 0.1-1 kW transmitted power is used, and the size of the antenna is limited by the size of your backyard. Let me share some photos of typical EME antenna systems from my friends here. (YU7AA, OM3BC, HG1W)

YU7AA om3bc hg1w

Using software instead of hardware

While it is possible to get good results by increasing the output power and the size/gain of the antenna system, there are other options as well. Recent advancements in signal theory and Digital Signal Processing (DSP) helped to leapfrog technology. It is now possible to develop and run advanced modulation and coding algorithms on a simple PC, which enables the reception of very low-level signals. One of the cutting edge technologies was developed in an open source community led by Joe Taylor, K1JT. Their software stack is called JT65, which has different sub versions with different features.

We already published some posts on using the WSJT software stack with Quadrus SDR:

Waiting for Moon-bounced signals

So, we decided to perform some practical experiments. One of our friends, QTH, is setting up some stations featuring V/H polar antennas. This is an ongoing process, and while Andy, 6NN, and I were waiting on this, we decided to set up our own simple station with a 6 element DL6WU yagi antenna fixed to 270 deg direction. We connected a Quadrus SDR receiver with some pre-selection filtering and low noise pre-amplification. The photo below, taken by Andy, shows the last element of the antenna and the Moon:

antenna 6nn moon and ant

So, now he has set up his receiver, and he just needs to wait for the Moon to enter the antenna beam. With luck some good QRO stations will transmit with enough power so even this simple station is going to be able to receive and decode.  I am excited to see his updates.

New Moon radar project

A couple of us have decided to repeat the original experiment by Zoltan Bay’s team on the anniversary in 2016. We already started to build a system including the antenna system with a half wave dipole array. Here you can see some of the 3D electromagnetic simulation results of one antenna patch. Stayed tuned!

full_dip3_hor1_2dg full_dip3_hor1_3dg full_dip3_hor1_cos

 full_dip3_hor1_epl full_dip3_hor1_hplfull_dip3_hor1_3dr

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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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WSJT-X and Quadrus | testing the new release

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WSJT-X and Quadrus | testing the new release

We got some news from Andy, HA6NN, on testing out the new WSJT-X with Quadrus. The testing is based on the latest v1.4 beta release of the WSJT-X using the DRU-244A Quadrus SDR hardware and the accompanying SRM-3000 SDR software. Let me share some very good screenshots from him – note that they include a couple of DX calls.

iz3wuc-w7nbh_1502261850ut wsjtx_1502261843ut

vk4xjb_1502252004ut                wsjtx-spec-1502252000ut

He kept his Quadrus equipped computer on during the night, and shared the list of stations heard on a video published here:

All these results show that the WSJT-X and the Quadrus SDR provide a suitable platform to receive digital signals and stream them to the back end processor, like the WSJT. Our development team is working on adding multi-channel Virtual Audio Connection (VAC) capability to utilize the real, multi-channel feature of the SDR. This would allow us to connect different instances of the decoder software to different channels on the receiver. First, it will only support 48 kHz IQ sampling rate, but we are working on the 96 kHz capability of the MAP65 and WSJT software stack as well.

You can read more about IQ samples and Quadrus SDR in this post:

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Quadrus SDR for DRM receiver in education

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AM and DRM broadcasts in the HF bands

Traditionally, AM modulation is used in the LW/MW/SW bands for broadcasting purposes. It is very easy to identify these the AM broadcast stations based on their Dual Side Band (DSB) shape in the spectrum. The spectrum and waterfall displays of the Quadrus SDR show such a modulation on the following pictures.

am spectr
am water

However, digital waveforms, i.e., DRM, have started to populate the HF bands, which can provide high quality content. The modulation format is optimized to the propagation behavior, and is based on the multi-carrier scheme. It is also very easy to recognize them in the band using the Quadrus SDR for DRM, because these stations have a distinct rectangular shape in the spectrum.


DRM in the telecommunication curriculum of universities

As DRM represents a significant part of broadcasting systems nowadays, most universities around the world have included this standard, or parts of it, into their curriculum on telecommunications. It is also an important part of the telecommunications program at the Budapest University of Technology and Economics as well, where we have recently introduced the Quadrus SDR for DRM by showcasing its DRM reception capability.

DSC_0478 DSC_0523

drm05 drm02



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Performance testing of Software Defined Radios

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Performance testing of Software Defined Radios

Do SDRs perform better than conventional Superhet architecture radios? A big problem is that many of the traditionally used tests, which compare radios on league tables and in reviews, are not very relevant to SDRs due to fundamental differences in technology.
A very good article on this topic by Andrew Barron ZL3DW
Performance testing of Software Defined Radios

We already published a post on the sensitivity of the Quadrus SDR here:

The published results are:
SSB -111 dBm at 10 dB S+N/N with 2.1 kHz bandwidth
CW  -119 dBm at 10 dB S+N/N with 400 Hz bandwidth

According to Andrew:

MDS (Minimum Discernible Signal)

MDS is a measurement of how sensitive the receiver is. It represents the weakest signal you can hear. You need it to be good if you want to hear very weak signals on a quiet band, for example when sunspots are poor or the band is closing. If the band is noisy the noise level coming in the antenna port will often be higher than the MDS so sensitivity is not as relevant.

In the test a signal is input to the receiver and the MDS is the input signal level when it shows as 3dB above the receiver noise floor. The MDS is better if the bandwidth of the receiver is reduced because a narrow bandwidth allows less noise in. So it is usually measured using a typical CW bandwidth of 500Hz and using a typical SSB bandwidth of 2.4kHz. It is normally checked on several bands as well. In most SDR receivers especially direct sampling (digital down conversion DDC) receivers you would expect the same performance on all bands. When you compare results relating to different radios, check that no attenuators or preamplifiers are in use. Most SDR receivers have an MDS better than -125dBm in 500Hz bandwidth and better than -115dBm in 2.4kHz bandwidth. Excellent receivers can achieve an MDS better than -130dBm in 500Hz bandwidth and better than    -120dBm in 2.4kHz bandwidth. SDRs with 8bit analog to digital conversion (ADC) will probably not be able to achieve that level of performance because of limited dynamic range.

It is not easy to compare the results, because we’ve measured in 400 Hz / 2.1 kHz bandwidth instead of 500 Hz / 2.4 kHz, and we’ve measured a 10 dB signal above the noise floor instead of 3 dB. However, we can do a very simple calculation of adding 7 dB to the 3/10 dB measurement level difference.

So our performance testing comparable to this reference article is:
SSB -118 dBm at 3 dB S+N/N with 2.1 kHz bandwidth
CW  -126 dBm at 3 dB S+N/N with 400 Hz bandwidth

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