Matching networks and tuners
When an antenna’s impedance is far from 50 ohms, a matching network transforms it so the transmitter sees a clean load.
What a tuner really does
An ‘antenna tuner’ does not tune the antenna — it transforms the impedance presented at the shack end of the feedline to something the radio is happy with. The antenna’s actual pattern and efficiency are unchanged.
Common networks
- L-network — two reactive components; simple and efficient
- Pi and T networks — wider matching range, used in many tuners
- Stub and gamma matches — built into the antenna itself
High-Q antennas
Some antennas are matched by a single tuned capacitor. A small transmitting magnetic loop resonates with a high-voltage variable capacitor and is extremely sharp — retune it for even small frequency changes. An end-fed half-wave instead uses a 49:1 transformer to tame its very high feedpoint impedance. Different problems, different matching tools.