Assuming your top-loaded vertical was close to resonance, the UnUn
application is not very demanding. I'm not sure what core material Balun
Designs use, but a quick calculation for 2x6 turns on a FT240-K toroid
predicts a core dissipation of 3.7W on 160m when handling 1kW, or
0.016dB loss - that's very probably less than the winding copper losses.
Steve G3TXQ
On 14/04/2012 18:42, Michael Tope wrote:
> Guys, I was testing their Unun. Although I do agree with what K9YC says
> about testing common-mode chokes, I just want to be clear that is not
> what I was testing. Also, I think thirty seconds key down at 1KW is a
> pretty good test for something with small thermal mass. I would have
> gone longer, but my amp is a Drake L-7 and I would be leery of running
> it longer than that (even 30 seconds is probably questionable). A loss
> of 0.2dB would be ~50 watts dissipation in the Unun. I claim that much
> dissipation would produce a noticeable temperature rise in the unun
> core/windings after 30 seconds. The goal of the test was to give some
> indication of whether the unun was going deliver the bulk of the input
> power to the antenna. On that score it passed IMO. I also didn't see any
> drift in VSWR while doing the CQ 160 CW contest, where contrary to what
> W6RMK would have you all believe (he's heard to many of my "fish
> stories"), I do CQ a lot with no answers :-)
>
> 73, Mike W4EF...
>
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