Spectrum Reference curve

Overview

• Usage of the spectrum reference
• Spectrum Reference Controls
• Interpreter commands for the spectrum reference

See also: Spectrum Lab's main index ,  settings dialog .

The spectrum reference can be displayed as curve in an overlay of the spectrum graph. The reference data can be taken from a spectrum which has been recorded previously, it can also be saved as and loaded from a file (as a TEXT file). The controls for the "Spectrum Reference" are explained later.

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Spectrum Reference Controls

The spectrum reference controls are located on a special tab in the settings dialog.

Visible graph

if checked, the reference spectrum is shown in the graph as an "overlay". The visibility can also be turned on and off through an interpreter command.

Color

Used to define the color of the reference spectrum (if visible)

Subtract

If checked, the reference spectrum will always be subtracted from the currently displayed spectrum (in the spectrum graph and on the waterfall).
This feature can be used to detect "slow changes" if used together with the following button:

Copy from current spectrum

Click this button if you want to use the actual spectrum as a new reference. The new reference will not be saved as a file automatically (you can save it from the "File" menu). The same function can be invoked as an interpreter command too.

Copy from long-term average

Similar as above, but this function copies the reference curve from the long-term average spectrum (instead of from the most recently calculated spectrum).

Notes and hints:

• To generate a "smooth" reference, use a very slow waterfall scroll interval in combination with the "optimum waterfall average" (in the "Spectrum display" menu), or turn on the long term average and copy the reference from there (after a sufficiently long time of integration, when the curve is reasonably smooth).
  For example, feed noise into your receiver and you will get the frequency response of the IF filters (etc) which you can save as a reference file (in the main menu under "File").
• The reference can be saved as a text file (extension usually ".REF"). You can modify such a file with a text editor, or with a spreadsheet program, or with the author's "Curve Editor". The latter is a tiny utility to view and edit array data stored in textfiles. Search the net for "DL4YHF's Ham Radio Homepage" or "DL4YHF Curve Editor" to find it.
• The interpreter command "spectrum.save" uses the same text file format as used for the reference curve.

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Interpreter commands for the spectrum reference

The following commands (and functions) for SL's command interpreter can be used to control the spectrum reference:

sref.pick

Picks the "curve" for the reference spectrum from the current spectrum in the main analyser, like the button "Copy From Current" on the spectrum reference tab.
Optionally, the source (channel) can be specified for this command, like:
sref.pick(#LTA1).  Other possible sources  (spectrum analyser channels) are listed here .

sref.visible=0,  sref.visible=1

Turns the visibility of the spectrum reference in the spectrum graph on (1, or any non-zero expression) or off (0, zero).  For example, the command line sref.visible = ! sref.visible toggles the visibility of the spectrum reference.

sref.load(<filename>)

Loads the spectrum reference (curve) from the specified file.

sref.save(<filename>)

Saves the spectrum reference (curve) as a textfile, from which it can be loaded later.

See also: Overview of interpreter commands, interpreter functions , numeric expressions .

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