[450] Problem solved! Balun issue!

[Bob]

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!

On Mon, Feb 3, 2014 at 3:26 PM, George Andrews <gandrews at ntplx.net> wrote:

>  Group,
>
>
>
> 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.
>
>
>
> 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.
>
>
>
> Some may already have an understanding of this, others may not be aware.
>
>
>
> 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.
>
>
>
> I have included a photo so you can see the incredible engineering of
> Unadilla baluns.
>
>
>
> 73, stay warm!
>
>
>
> George
>
> N1YAE
>
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>
>
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