I agree with what your are saying, except for the part about the test
being inconclusive. I was try to make a quick assessment of whether the
Unun had significant loss (say greater that 0.5dB / 10%). Based on the
result, I'd being willing to bet money that the loss is less than 0.5dB
(100 watts dissipation in the Unun). Now if you wanted me to bet money
on it being say less than 0.2dB (5%), I'd probably want to do a better
test incorporating your and W6RMK's suggestions just because I am loss
averse (no pun intended) even though I still think the odds are good
based upon my crude test that the Unun loss is less than < 0.2dB.
When I get my Alpha 91B fixed, I'll do a much harsher test :-)
73, Mike W4EF................
On 4/14/2012 12:00 PM, Hank Garretson wrote:
> 1. There may or may not be significant losses in the core.
> 2. There may or may not be significant I-squared-R losses in the wire.
> 3. The cover was off when you did your test.
> To me, all three items plus others make your test inconclusive.
> It's a heat-transfer calculus which is very complicated.
> You don't know how much heat was radiated to ambient air instead of
> accumulating in and heating the core. You don't know how much heat from the
> wire made it to the core. Thirty seconds is a very short time for heat
> transfer and accumulation.
> My recommendation is to check the balun under your typical worse-case
> operating conditions. Thirty seconds key down is one data point, but I
> wouldn't bet my balun on it.
> Hank, W6SX
> On Sat, Apr 14, 2012 at 10:42 AM, Michael Tope<W4EF@dellroy.com> 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 :-)
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