The design point: Feed-point impedance is the complex voltage-to-current ratio at the antenna feed point, and the installed value includes geometry, ground, supports, nearby conductors, return paths, and frequency.
Why the complete system matters
A handbook value assumes a defined ideal geometry. Height, slope, leg angle, coax shield current, moisture, and structures can change both resistance and reactance.
The assumption that breaks it
Quoting “73 ohms for a dipole” or “high impedance for an EFHW” as a fixed property can produce the wrong transformer or tuning plan.
Build or deploy it correctly
Measure at the actual feed-point reference plane in final geometry, document the complete current path, repeat after weather or height changes, and match the observed load range.
Configuration boundary
Use the exact product guide, electrical topology, geometry, materials, loading, feed, return path, support, and environment. Mechanical fit or a visually similar arrangement does not establish electrical equivalence.
