A second measurement at a known mismatch settled both the index and the scale.
At SWR 1.1: RM6=0. At SWR 1.5: RM6=52, while RM4 kept tracking the power.
52/255 = 0.204, which is the reflection coefficient of a 1.5 SWR to three
decimals. So the raw value is rho scaled to 255, and the ratio is
(1+rho)/(1-rho) — physics, not a curve fitted through two points, which is why
2.0 and 3.0 fall out of it correctly without ever having been measured.
The panel now shows that ratio, the number the operator reads on the rig, rather
than a percentage of meter travel — and a dash while receiving, since a stale SWR
from the last transmission reads as a live one.
Both measurements are recorded in the code and in a test, so the mapping is
evidence rather than a table borrowed from another model — which is exactly how
it came to read 81 in the first place.
rouggy
bdda7ad07a