On the comments about balun heating/QRO, even for guanella current baluns with
lower loss cores like Type 61 or 43:
I like this topic, because I've been wrestling with that issue for a 6:1 or 9:1
impedance match for a N6LF antenna.
Feedline is ladderline. I actually wound three bifilar 6" diameter air core
coils I was going to use to make a huge 9:1
guanella balun, because of this loss issue, but decided that a commercial model
based on cores (from DX Engineering)
looked like it would work well. (heck, I started wondering about the loss I
was going to get because of the length of
the wires in my 6" coils too)
Sure there's some loss transmitting with the ferrite cores in a current balun.
The thing is we should just count the dB,
right? Especially if just being used on a single band. Why stress about higher
frequency behavior if not being used
there?...(I'm targeting 80M)
We have heat loss everywhere, at some scale. Why are we stressed about the
balun? Mostly because of bad history in balun
design, right? And the use of baluns in situations far from their target
impedance. Or with not enough choking impedance
at the target frequency. Or antennas more unbalanced then we thought.
But let's look at what's fundamental solvable vs unsolvable.
We accept some dB loss if we have a long coax...it's just that the heat loss
there is distributed, so we don't worry
about it.
This particular heat loss is concentrated in the balun, and there's a history
of poor thermal construction for baluns.
Not enough core material. Plastic closed containers. Etc.
What's wrong with losing 35 watts at a balun, (.1dB out of 1500W say) as long
as there's enough ferrite material so the
cores don't see a heat rise that changes the core behaviors, or melts
insulation, (note that all the good baluns are
moving to teflon insulation) and there's enough air flow or other thermal
transfer? Heat is not necessarily the problem.
Heat dissipation can be.
If the Balun is up in the air and in the direct sun, there are issues about
raised temperatures due to that also. But
with ladderline, the balun isn't usually at the antenna?
Maybe the real problem here is the inability to measure things well. i.e. we
don't have techniques to tell us when the
end result is operating in a situation a lot different than we expected.
Wouldn't it be cool to put temperature sensors on a core in a balun, and get
remote temp sensing at all times? Then we'd
have a lot more real-world information about this core heating issue, rather
than lab data.
-kevin
ke6rad
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