/diy/ - Do It Yourself

>>1730762
Manual antenna tuners aren't so bad to make, the real challenge is sourcing the variable inductors. You're totally right though- tune at low power before applying full output is standard procedure.
>>1730766
Near the bottom of said article:
> Transistor rigs usually do not have any tuning adjustments. To avoid the extra heat created when running a de-tuned amplifier, there is a protection circuit that will significantly reduce the output power if the SWR is high.

If the antenna system isn't resonant at the RF frequency desired, the energy HAS to go somewhere. It will do anything it can to find the lowest potential point. Some radiates into space at poor efficiency, the remainder of the wave sees the transmission line as being effectively a short, and is reflected 180 degrees out of phase back through the antenna and feedline. This can cause a steadily ramping voltage on said transmission line, which eventually puts the final drive transistors into avalanche breakdown- something they're not designed for, and damage occurs. In tube based radios, high SWR can mean high voltage in places you don't want it to be; and you end up with stray RF in places it shouldn't be- the chassis, nearby metal objects, etc.
It's possible other L and C elements in the radio dissipate the energy as well, again not being designed to take induced back voltages, bad things happen.
>>1730764
Need to find the source of the problem first. Is it the power supply, or coming directly from the monitor? Any ground loops present? Clamp on ferrites with the cord going through them multiple times is a good start; but if it's coming from inside the monitor, you might need either electrical isolation and/or extra shielding.
>>1730767
If only you knew how many RFI/EMI problems I've solved with ferrite beads. Too many ferrites is a another fun one, you can literally take the edge off of a square wave.