Spectrum Lab Application: Beacon Logger
By Wolfgang Buescher, DL4YHF
Last modified: October 12, 2001.
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This application is used for propagation studies on shortwave. Radio amateurs all over the world operate becons on certain frequencies (like 14.1 MHz). These beacons periodically transmit a carrier and their identifier in Morse code. Some of these beacons have a very low duty cycle but a precise interval, for example 1 second carrier and 3 minute interval. This application takes precise readings of the signal strength, and writes the result into a text file which can be post-processed with a spreadsheet program etc.
The settings for the two beacon-logging applications (presented below) can be loaded from configuration files which are part of the installation package. They are called "Beacon1.usr" and "Beacon2.usr". You can load them from Spectrum Lab's file menu as explained here, or add new entries to SL's quick settings menu as explained here. The latter allows you to quickly switch between different settings.
A more recent beacon-logging example (from 2005) for the experimental MW beacon DI2AG can be found in a separate document (only in german language so far).
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If the beacon you want to monitor has a very stable interval, try this (or load the BEACON1.USR example into SpecLab from the "Quick Settings" menu):
There is one problem with this approach: you must precisely start the export function to catch the key-down phase. If your PC's clock or the beacon's clock is drifting a bit, the "sample slot" will slowly move away from the beacons key-down phase, no matter how precisely you measured the beacon's cycle time.
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To catch the carrier amplitude of a beacon with low duty cycle without the need for precise timing, there is a different solution which will result in a very clean exported file. Principle:
In Spectrum Lab, the steps described above can be performed simultaneously for many different frequency ranges. The following interpreter commands must be entered in the export configuration dialog to do the job (or load the BEACON2.USR example into SpecLab from the "Quick Settings" menu) :
2of the export file = line
2of the definition table):
2, and returns the maximum of both values which will be the "new" value for this colum. It you entered this in column 3, you would have to use index  in the expression).
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