wiki:Manual/DataTypes/EmissionMasks

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Emissions mask

Click on the below links to get directly to the following sections of this page:

Dialog window

The emissions masks dialog window is designed to define parameters of different spectra of emissions for:

  • unwanted emission of transmitter or
  • its unwanted emissions floor.

The emission mask dialog window looks like this:

An emissions mask function is always defined by a sequence of triplets (x, y = f(x), z) displayed in the emissions mask grid where f(x) stands for the relative emitted power (in dBc) at frequency offset x (expressed in MHz), measured in a reference bandwidth z (expressed in kHz). A full description of the calculation of total emissions (including unwanted emissions) of IT falling in VR bandwidth is available in a separate page.

Two curves are displayed:

  • One shows the actual curve of the mask, for given reference bandwidth z, that is:

y = f(x)

  • The other one shows the curve normalized in a reference bandwidth of 1 MHz, that is:

y = f(x) + 10log(1000/z)

The latter curve is aimed to detect potential discontinuities in the definition of transmission mask, and is also the one which is used in actual simulations when integrating the total power of unwanted emissions, in order to overcome possible differences of victim and interferer bandwidthes.

The following functions are available in the dialog window:

  • Add: To add a triplet click on Add button. Triplets are then automatically sorted by increasing x value,
  • Delete: To suppress a triplet at marker position, click on Delete button,
  • Sym: To symmetrize a transmission mask, click on Sym button, this results in generating for each triplet (x, y, z) a symetric triplet (-x, y,z) if it doesn't already exist,
  • Load: click on the Load button to load a mask from an external text file. This file must contain one triplet (x, y, z) per line, with values TAB separated.
  • Save: If you want to save the defined mask for future re-use or sharing with other users, click on Save button to export the defined mask grid to a text file.

Important note

The value of reference bandwidth is therefore extremely important as it has direct impact on the calculated unwanted emissions level. Unless the reference bandwidth is separately defined as a part of mask definition (e.g. for mask definitions in radio equipment standards, etc), the user is advised to enter the total emissions bandwidth of interefering transmitter (i.e. channel width) as value for reference bandwidth.

Library

SEAMCAT contains pre-defined spectrum mask library that you can use directly or you can edit yourself.

Testing your mask

You may check the definition of unwanted emissions mask by calculating the actual unwanted emissions for given mask in a given victim receiver bandwidth and at a certain IT-VR frequency offset using a particular test feature by selecting the Test Rel. Unwanted command from the Workspace menu or click on the icon of the toolbar () or CTRL+SHIFT+U as shown below:

This feature allows you to directly extract the uwanted emission by entering the frequency separation, the receiver bandwidth and the spectrum mask as shown below:

Attachments