Radio frequencies (just a quick look)


We aren't modelling radio telescopes in detail in this trail section, so the following analysis is just enough to be able to complete our basic overview of the EM spectral regions. The target snippet is:

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The RegionEM has ranges stated in wavelengths in nm, which was convenient enough for visible light, but not ideal for radio frequencies. The value properties fMin to fMax use the ValueType frequency[gigahertz] and Unit gigahertz already available in the ISO-80000 ModelLibrary, and readonly values have been assigned within redefined fMin to fMax within RegionRadio.

It would be nice to be able to use either wavelength ranges lMin to lMax or frequency ranges fMin to fMax, but if we do that we need to make sure that if both value sets are populated they agree. Constraints for the relationship between frequency (f) and wavelength (λ) can be elicited from the following:

Where the speed of light c is held by a common block of Constants:

This gives us basic UML-style Constraints on block RegionEM, which must be satisfied by any valid instances:

{lMax = constants.c / fMin}
{lMin = constants.c / fMax}

Consistent values for lMin and lMax have been assigned in readonly redefinitions in block RegionRadio using an online resource frequency converter resource, with the SysML Trace relationship used to indicate where the values come from.

However, we can also use SysML Parametrics to calculate them. For example, given fMin and fMax we can calculate lMax and lMin. But because this is Parsing Analysis tutorial, we don't want to overwrite values that have been stated as elicited from snippets, so instead some value holders /calc_lMin and /calc_lMax are used, which we can use to compare with the stated values as shown next .

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