oresat-c3-hardware/doc/RF and Microstrip notes.md

We use OSH Park 4 layer PCB. 50 ohm line on this is 0.38 mm, as we determined by calculation and by measurement.

Decided to move RF net clearance to 0.75 mm which is ~ 4x the dielectric thickness of 0.17 mm. Better than minimum of 3 and worse than the 5 some people say.

The 0.75 mm clearance means that the total RF "width" of the strip and pulled back ground plane is 0.75 * 2 + 0.38 mm = 1.88 mm.

The TSTOP on the RF traces is 1.6 wide, which protects the ground copper with 0.18 mm of coverage on both sides.