So I cooked a set of finals recently with no obvious reason why.? Most of time my radio uses my raingutters as the antenna, which means I'm using a 9:1 unun with my ATU100 tuner.? When I switch bands the tuner takes a second to do it's thing and for a brief period of time the SWR and power output can be very high.? Gyula mentions that he uses a current limited power supply to reduce these power spikes.? That got me thinking.? I found a chip and made a quick design which could be placed between any standard power supply (battery, AC/DC converter, etc) which would limit the maximum current drawn from the source.? I got a decent way into the PCB design, but then this morning on my drive to work, I got thinking that this approach maybe doesn't do anything...? Help me understand this, I may not have this right in my head:
When transmitting the SDR controls the voltage going into the mosfets in the PA.? The signal goes out the radio hits the antenna and we'll say that this antenna has a very high SWR.? Which means a large portion of the power sent out gets reflected back to the mosfets.? Is that incoming reflection the power increase that we see?? Or is high power during high SWR increasing voltage at the mosfet and pulling more current from the source?
If it's from the source, then I think I can complete this design and have a simple way to add a bit of protection.? If it's just from reflected power, then it's a matter of turning down the drive while tuning, I assume.
