End whistling into your mic with this suggestion from David GW4AKZ:
When using an antenna tuner on SSB, we could easily add a tone generator and switch to do that.
I have fitted a switchable -6db pad between the output of the pcb and the antenna socket. With the circuit switched in the worst case SWR is about 1.65 to 1 with an open or short circuit. This prevents the finals from ever seeing a poor SWR.
Tune is easily achived with the key down and reduced radiated power when tuning up.
I use 2 watt carbon resistors 33 ohms in a t attenuator circuit. 2 in parallel to give 16.5 ohms which is close enough to the calculated value. A relay is s used to switch this attenuator in and out.