On Dec 30, 2024, at 10:33, Roger Need via groups.io <sailtamarack@...> wrote:

On Mon, Dec 30, 2024 at 01:58 AM, G8HUL wrote:

The Tx does not see an SWR it sees an impedance, it is the transmission line
that has the standing waves and that must be based on the impedance of the
line NOT the load that the Tx 'likes to see'.

Yes it is the transmission line that has the standing waves on it. However as I stated in my previous post the transmitter power amplifier is designed for a specific load which is 50 ohms for ham transmitters. Modern solid state transmitters contain a circuit that calculates SWR based on the load impedance at the output connector on the Tx. The Tx circuitry cuts back on the output power as the SWR rises.

Maybe. It kind of depends on the amplifier - some just fold back when the voltage at the output terminals gets too high (to protect the transistors). That is, the protection circuit on most amps doesn’t actually calculate the SWR - it protects the devices against whatever the limiting parameter is (voltage is the quick death, current or heat is the slow death).

Imagine an amplifier with zero output impedance.