Is this a step up balun on an end fed? That is a little tougher to find a suitable non-balun replacement for, but for most things there is always a way to eliminate that weak link. I'd put my efforts in that direction and go QRO as soon as possible! <br>
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<div class="gmail_quote">On Mon, Feb 3, 2014 at 3:26 PM, George Andrews <span dir="ltr"><<a href="mailto:gandrews@ntplx.net" target="_blank">gandrews@ntplx.net</a>></span> wrote:<br>
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<p class="MsoNormal">Group,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></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. <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></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.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Some may already have an understanding of this, others may not be aware. <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></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.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I have included a photo so you can see the incredible engineering of Unadilla baluns. <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">73, stay warm!<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">George<u></u><u></u></p>
<p class="MsoNormal">N1YAE<u></u><u></u></p></div></div><br>_______________________________________________<br>450 mailing list<br><a href="mailto:450@lists.vhfwiki.com">450@lists.vhfwiki.com</a><br><a href="http://lists.vhfwiki.com/cgi-bin/mailman/listinfo/450" target="_blank">http://lists.vhfwiki.com/cgi-bin/mailman/listinfo/450</a><br>
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