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Re: [TowerTalk] Balun Overheating?

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Balun Overheating?
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 21 Apr 2014 09:47:22 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 4/21/2014 5:32 AM, Jim Lux wrote:
The real sticky issue when trying to calculate stuff is "what is the voltage". And that's something that is hard to determine in a simple way. One can do a numerical model (using NEC, for instance), but in practice it's highly installation dependent.

YES! NEC will at least get you in the ballpark if the model you enter is close to your reality (like feedline length). But antenna imbalance increases the common mode voltage (and thus the common mode current), and those imbalances can be hard to model, because they come from things like ground slope, variations in soil under the antenna, surrounding metal objects (wiring in your home, adjacent antennas and even adjacent feedlines).

All of which are reasons why I've always taken a brute force "more is better" approach to designing for high power. If you buy them right (in quantity from vendors who specialize in Fair-Rite products, you should be paying no more than about $5 for a #31 2.4-in o.d. toroid, tax and shipping included). And all it takes to buy them right is a group purchase with one or more local ham clubs. I recently did a very successful group buy with Dexter Magnetics, near Chicago, and I've seen good reports about Lodestone Pacific.

73, Jim K9YC
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