Producing suitable bitmaps
Colours in bitmap files are often written as red,green.blue as in 26,239,179 indicating the amount of red (26), the amount of green (239) and the amount of blue (179). Amounts vary from 0 (none of the colour) to 255 (the maximum possible amount of the colour. Often the colours are written in hexadecimal format as 0x1aefb3 or 0x1AEFB3. Such a colour will look like this.
It is absolutely essential that you are able to produce bitmap images with exactly the colours
One conductor must be produced in pure red. i.e 255,0,0 or 0xFF0000. This red will look like the red square on the left. The one on the right is very slightly different, having a very small amount of blue, and so has the colour representation 255,0,1 or 0xFF0001. The colour on the left will be interpreted by
Graphics packages such as Gimp (freely available for no cost on unix systems) will allow you to set a colour precisely.
You then need to draw an image of the cross section of the transmission line to be analysed. The scale can be anything you reasonably want, but should result in the largest dimension in your transmission line have 200 or more pixels allocated to it. Making the bitmap much smaller (say 32 pixels in one dimension) will results in fast but inaccurate results. Much larger bitmaps, say 1000x1000, will take a long time to compute. The bitmaps don't have to be square. You should aim to fill the whole of the bitmap with the relevant details, and not have a lot of unused space on the bitmap. For example, the image on the left below is fine, but the one on the right will spend a lot of time computing nothing of value.
Predefined colours in
The input file to atlc, which is a bitmap, must have the correct colours to indicate what parts of the image are conductors and dielectrics. Parts at ground (0 V) potential must be drawn green, those at +1 V must be drawn red and those at -1V must be drawn blue. Only red and green are noramlly used for conductors, with blue being used only on couplers. Vacuum dielectric must be drawn while. Many other colours have very specific meanings as shown below.
RT duroid 5880
PVC (at 1MHz)
RT duroid 6006
RT duroid 6010
Er of 100.0
atlc, having another permittivity very close to 1.0 is useful, as for test purposes. The figures for the plastics given above are only approximate. The permittivity of plastics are usually frequency dependant and temperature dependant.
atlcwith the following command line option.
atlc is written and supported by Dr. David Kirkby (G8WRB)