I already got some feedback as to what might be causing my problem but I wanted to hear more thoughts on this. I have a horizontal delta loop that I use on 20 meters. When I use to tune up on that band and run my amp I had no issues for a long time. Now...I cant seem to tune up and run my amp on that band because when I increase the power output to over about 500 watts the radio cuts out. I have no issues when running 100 watts, but when I use the amp and increase power its like someone pushed the on/off switch on my ic 7300 and it goes off and then back on????....by the way my loop is fed with 450 ohm window line to a 4:1 balun and then a run of coax into the shack. oh yeah...the swr is 1:8:1 with no tuner....although I do use a tuner rated for 1kw when I operate. Someone told me that it could be a bad balun? but as I mentioned I have no problem when running 100w just at higher power....any ideas?