High frequency start can interfere with radio!! not sure if it will effect your setup though.

I fitted a small pot to my tig torch, I roll this with my thumb, I did this due to a foot injury…….

I wouldn't bank on any radio link working within range of a wide-band spark-gap transmitter = welder.

Neil

One method that MAY work would be to do the following. In the pedal unit have a potentiometer feeding a voltage into the ADC input of a micro controller (Such as an ATtiny2313.) Then output this via the serial port as an 8 bit value to a Bluetooth module which has been paired with another blue tooth module. The second Blutooth module would be connected to a second micro controller at the welder end. (Again via the serial port.) The second micro controller would need to have a built in DAC converter to convert the 8 bit value back to a voltage. (Or you could build an external DAC.) You would then need to find out how to interface this voltage to the welder. (You would need the schematic of the welder.) As Andrew says close to an electric welder is a very harsh environment for radio communications so Bluetooth may not work. Before you start you cold see if a Bluetooth linked worked close to the welder with a laptop and a Bluetooth device. (Such as a Bluetooth keyboard.) Another possible approach would be to use a model radio control transmitter and receiver with with a servo driving a potentiometer. Using infra red communication between the pedal unit and the welder might also work if the receiver was well shielded from the light from the welder. For either of these methods you would need to learn electronics and possibly programming micro controllers. So unless you want a real challenge I agree with Andrew that you should stick to a wire link.

Les.