Update README.md

extras/cad/README.md

@@ -4,7 +4,7 @@
 - `antenna_base` - base for rubber duck antenna, to be printed with PETG filament.
 - `antenna_cover` - cover for rubber duck antenna, to printed with TPU filament.
 
-👉 Rubber duck antenna spiral widing was done with 1.3mm copper wire on 8mm aluminium scaffolding tube.
+👉 Rubber duck antenna spiral widing was done with 1.3mm copper wire on 8mm aluminium scaffolding tube, ~8 turns with 6mm step
 
 **Tracker case**:
 - `aprs_tracker_e22_base` - base for tracker case without battery compartment.