Mike,
I'm not a betting man, but if I were I'd bet heavily that those UnUn
losses are significantly less than 0.2dB. Here's my reasoning:
The core in the Balun Designs photo looks to be about a size 140 with 6
turns of coax on it; but we don't know what the core material is, so
let's take two extremes from a loss perspective: #61 and #43.
Secondary impedance of a FT140-61 UnUn with six turns measures 0.6+j277.
Handling 1kW into a well matched load, the secondary voltage is 224V
rms. So the loss in the UnUn is 392mW or 0.002dB
Secondary impedance of a FT140-43 UnUn with six turns measures
318+j1677. Handling 1kW into a well matched load, the secondary voltage
is 224V rms. So the loss in the UnUn is 5.48W or 0.024dB
As I said in an earlier posting, your application is very benign for the
UnUn: the impedances, and therefore the voltages, are low; and down at
160m the loss component of the winding impedance is low compared to the
overall reactance.
If the UnUn were handling a more "challenging" load, things would be a
lot different. A while ago I measured the performance of UnUns made from
various mixes when connected to a 40ft wire used as a non-resonant
multiband vertical; you can see the results here:
http://www.karinya.net/g3txq/unun/
73,
Steve G3TXQ
On 15/04/2012 16:47, Michael Tope wrote:
> Hi Hank,
>
> 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................
>
>
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