Background

In this post we show how to set a streaming radio to remotely listen to airport radio.

SDRNode configuration

The SDRNode server is set to receive radio using an AirSpy SDR receiver and is connected to a discone antenna. System is configured to stream the IQ SDR samples on a bandwidth of 50 KHz, knowing that AM transmission between aircrafts and control tower is around 9KHz wide. Next picture shows the setup we have:

The SDRNode boot script (sdrnode.js, see this page for more details) is set as follows :

[code language="javascript"]
// SDRNode configuration code
function setup() {
 for( i=0 ; i < sources.length ; i++ ) {
  var sourceDef = sources[i] ;
  print( '--------------------------------------');
  print( 'Source ' + i + ' UID=' + sourceDef.UID );
  print( 'Source ' + i + ' name=' + sourceDef.name );
  print( ' Center Frequency =' + sourceDef.center + ' MHz');
  print( ' Tunable from ' + sourceDef.fmin + ' MHz to ' + sourceDef.fmax + ' MHz' );
  print( ' Current sampling rate : ' + sourceDef.sr/1000 + ' KHz' ) ;
  if( sourceDef.name == 'AirSpy' ) {
	var airspy = new RFSource( sourceDef.UID );
	airspy.setPublic(true);
	airspy.setRxGain( 0, 7 );
	airspy.setRxGain( 1, 6 );
	airspy.setRxGain( 2, 7 );
	var rx = airspy.createStream( 50e3, 'SPY@F4GKR' ) ;
	rx.setCompressionType(3) ;
	rx.setPublic(true);
  }
 }
}

Then, using the SDR Client software (or any “EXTIO” DLL compatible software like HDSDR #etc., see Wiki here for details), we can connect to the streaming server and rectrieve the IQ samples to process them as we want

CloudSDR client software is used here to record to an mp3 file the decoded audio. You can listen to it here (Orly Airport coordination frequency, 123.875 MHZ, AM, recorded on August 2016, the 9th, at 12:00 localtime).

Orly MP3 remotely recorded

CloudSDR client has “location awareness” and knows where are the SDR streaming sources. A map shows the different servers you can connect to and shows known radio stations, like Airports for example :