The antenna chain: SWR and tuner

What sits between my radio and my antenna, and why?

Between a radio and its antenna there are usually two helpers. The order is worth memorising, as the exam shows it as four numbered blocks.

The order

From the radio to the antenna:

1. Transceiver
2. SWR meter
3. Antenna tuner (ATU)
4. Antenna

What the SWR meter does

The SWR meter measures the standing wave ratio on a transmission line, which shows how well the antenna system is matched to the radio.

• Low SWR: efficient power transfer to the antenna.
• High SWR: power loss, and possible damage to the transmitter.

What the antenna tuner does

The Antenna tuner (ATU) matches the antenna system's impedance to the transmitter's output impedance, which is typically $50\ \Omega$. That gives maximum power transfer and a lower SWR.

You now know

• The chain is transceiver (1), SWR meter (2), antenna tuner (3), antenna (4).
• The SWR meter shows how well the antenna system is matched; low SWR is efficient, high SWR loses power and can damage the transmitter.
• The antenna tuner matches the antenna system to the transmitter, typically 50 ohms, for maximum power transfer.