Tagged: sdr software


SRM GUI tips and tricks series – RF record and playback

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Hi Everyone,

We at Spectrafold thought it would be helpful for the community if we provided some tips on how to use SRM – even the simpler functions. This is the first piece of this “tips and tricks” or “best practices” series. We are going to look into record and playback this time. Playback and recording will be essential for both amateur and professional SRM use.

For testing purposes I am always using the latest stable release of our software (release 20150415 at this point), which you may get from our support site: http://spectrafold.com/quadrus/support/

RF Record and playback

Looking into the RF record and playback functionality, one will quickly realize that most of the time we deal with .DSRS binary files (essentially saved samples), which are unique to SRM as an IF file type. I will cover audio recording in a separate post.


We have recorded and shared some IF spectra in a prior blogpost. Feel free to download any of them -  I have chosen 14100+-100KHz-20140316-111835-0984.DSRS, because it has a 200 kHz bandwidth.

You may open and load such a file in SRM by selecting FILE as an input method, then choosing the appropriate file from your hard drive or other location. Start playing it by clicking on ‘Start’.


The user may freely change a number of functions while listening, for example:



You may choose from the following demodulation types:

  1. AM – amplitude demodulation
  2. USB – upper sideband (single sideband) demodulation
  3. LSB – lower sideband (single sideband) demodulation
  4. ISB – independent sideband (or Kahn method) demodulation
  5. FM – frequency demodulation
  6. CW – continuous wave demodulation
  7. IQ – ‘I’nphase ‘Q’uadrature demodulation

If you are using the IF spectrogram (or ‘Waterfall’ as it’s colloquially called), you may want to understand the use of Reference signal strength and the AutoMax/AutoMin functions. You may re-shape the appearance of your waterfall with these, which is very useful to find weaker signals and to separate them from noise more effectively.


Please note that recorded files will be played back continuously and restart unlimited times.


SRM will record into the same DSRS files, which we have discussed at Playback. Firstly, I would recommend to set up a proper folder to save into, which may be done on a per channel basis.


Then you choose the spectrum type in Control -> Recording as shown.

SRM_tips_01_setting_IF_capture_settings_01Recording will start as soon as any source starts feeding data to SRM – just hit the start button. In my case, seen below, I have been generating a known signal with the Internal Generator, to make sure I get the exact same result back.


Saving a spectrum is quite storage intensive: a 1 minute long recording will be approximately 30 MiB with 100 kHz bandwidth. Also, note that due to longer buffering times, your file will appear somewhat later after recording. In my case, it was some 30 seconds after recording stopped. You may close SRM to ensure your file is saved.

The files follow a naming convention:


{filetype IF/AF_channel number-/YYYYMMDD/-/HHMMSS/-/code/}


Feel free to download the SRM-3000 SDR software receiver from the support page and some recorded IF files with different bandwidths from the 20 m and the 15 m HAM radio bands. Using the recordings feels like having actual receiver hardware under your SDR.

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CW Skimmer – Quadrus SDR

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What is a CW Skimmer?

A CW Skimmer is multi-channel CW decoder and analyzer by Alex, VE3NEA. You can read about this great tool and his other works on his website: http://www.dxatlas.com/CwSkimmer/

A great tutorial is available from Pete, N4ZR as well: http://www.dxatlas.com/CwSkimmer/Files/Skimmerintro.pdf

Go ahead, and look at the links if you are not familiar with the topic.

How to connect the CW Skimmer and the Quadrus SDR ?

The CW Skimmer is accepting signals from radio receivers. The traditional hardware radio can be connected through a sound card audio input to the software, and the CW Skimmer software can remote control the receiver on CAT. The bandwidth, in this case, is limited to the usual 3 kHz of typical HF radios.

However, the CW Skimmer software can handle a couple of SDRs too, and can accept higher bandwidth signals from them. Some of the SDRs on the market can also be controlled from software trough their APIs.

Today the CW Skimmer – Quadrus SDR connection is not supported directly by the CW Skimmer. Thus, we have to use the simple audio interface connection. This limits the analysis bandwidth to 3 kHz. Because the SRM-3000 SDR receiver is software too, we can use a virtual audio cable to connect to the CW Skimmer. I’ve used the VB-Cable A&B from VB-Audio Software for my tests. A single connection is free for non-commercial use.

Decoding calls in the 20 m band

Yesterday, I had a chance to use one of the remote stations with TeamViewer. It is located in the country side with a simple inverted-V shaped G5RV wire antenna. I found a spot around 14.025 MHz in the CW band. There were a lot of stations in the 3 kHz bandwidth. The outcome of only a couple of minutes of recording can be seen below with the call signs collected by the CW Skimmer.


Further improvements with server version CW Skimmer

There is another software from Alex called CW Skimmer Server. This application can handle up to 192 kHz bandwidth in seven ham radio bands. The SDRs can be connected with a 3rd party driver. We are looking for interested programmers to provide a driver to CW Skimmer Server based on the TCP/IP remote control interface of the SRM-3000 SDR software receiver.

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