>
>> Then we just run a few kW through it and see if the core heats up, and we
>> measure how much power comes out the other end.
>>
>
> Yes, this is a meaningful test that can be run rather easily. N6RK has
> suggested
> that in addition to the choke under test, a coaxial choke wound according to
> my
> guidelines should be added to the line to insure that the common mode
> voltage/current is small. That makes sense to me. Indeed, if it is done, you
> don't need a dummy load, you can do this with any reasonable antenna.
>
> 73,
>
> Jim K9YC
Okay, here's my problem.
I know I don't know this stuff.
But I've tried to read everything I can find on the web. Including Jim
K9YC's excellent amount of information at his website.
But then I read something like W1CG's low power 4:1 current balun
article, where he tested it with a procedure that seems good, that
includes a temperature rise test inside a vacuum bottle, correlated to
the temp rise caused by a non-inductive resistor load. (see test for
details), to get loss/efficiency numbers.
So he's done something like the temp test we're asking about (for a 4:1
current balun, but the issues are the same)
http://www.njqrp.org/balun/Balun%20Manual%20-%20final.pdf
page 5 of 7 starts the testing description. I'd be interested in what
people think about the test methodology and results.
He points out that the losses vary with the output load. If close to
target impedance, losses aren't bad..i.e. 3% or 0.12 dB.
This correlates to the 30 watts at 1000 watts kind of ballpark I mentioned.
If instead, the load is 714 ohm reactive (instead of 200 ohm) losses
double to 6%. (.27 db)
This is a two core Guanella 4:1 current balun. Type 43 mix.
So what I'm wondering about:
Have people been talking about the heat and loss generally, without
bounding it, for specific loads and frequencies (and designs)?
And using the general experience of poorly designed baluns historically,
to support the case, when really that's not fair?
When looking at a specific case, the heat loss is manageable. Especially
if the load matches the design goal.
However the balun has to be designed for heat dissipation, and
additional cores may be necessary to avoid overheating the material.
Passive cooling should be sufficient, if the enclosure is designed for
it. It probably means you don't want weatherproof enclosures. But the
ladderline goes to the shack, and the balun can easily be in a weather
protected area (overhang etc).
W1CG mentions in his conclusion, that a larger balun (more ferrite
material) of a less lossy material, would probably work well for QRO.
(he used type 43)
Thoughts?
-kevin
ke6rad
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|