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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Group,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I found the reason for my antenna problem. A Unadilla balun came with the antenna, probably typical for a number of commercial dipoles and wire antenna. The Unadilla baluns are rated at 2kW. One would think that should not be an issue when using only 600W sideband. What I did not think about is that the 2kW rating is for antennae with 3:1 SWR. Once the antenna SWR is over 3:1, derating is required. On 40 M, my calculated SWR is 3.4:1. This is apparently enough to cause heating over a couple of months that resulted in a breakdown of the insulation in the balun. As the balun was inside the house, I often checked its temperature by touch and also with a thermistor attached to the side. I never observed a significant deviation from ambient. There is air space around the core and the PVC is probably a good thermal insulator. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>SSB is about 30% duty cycle, so that is about 200W CW. Not a lot when considering the unit is rated at 2kW. Information is not available for a derating curve. 3.4:1 is not what I would regard as that far from 3:1. Some SWR calculators even report that as 3:1. I was advised that one should not run more than 100W into a Unadilla balun. That is likely good advice. Most baluns are outdoors, so that may prolong the life. I will either build or buy something like Balun Design units in the future. Unadilla will only see QRP power levels from here on out unless I can obtain derating info.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Some may already have an understanding of this, others may not be aware. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am back on the air with 100 W and expect the new balun to arrive in a day or two at which point I will be back on with 600 W capability.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have included a photo so you can see the incredible engineering of Unadilla baluns. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>73, stay warm!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>George<o:p></o:p></p><p class=MsoNormal>N1YAE<o:p></o:p></p></div></body></html>