Ian Jackson wrote:

But how good is the efficiency when the balun/transformer is working
between completely the wrong impedances (which will be most of the
time)?

I use a 4:1 balun under such conditions. I use it simply to make my autotuner
happy (which makes bandhopping easier). I have run extensive tests with the
balun in and out on the HF bands and have yet to find anyone on the other end
who could tell a difference.

My understanding (and limited experience) is that most of your
power simply heats up the ferrite.

My KW rated balun does get warm, even at 50 watts on some bands.

Of course tuners can also eat up considerable power on large mismatches. If you
want (or need) a simple antenna system to work on all bands then you will likely
have to absorb some loss no matter how you do it to get there. And the reason
many don't have a big problem with this is even if you do lose *half* you power,
that's still not a real big difference on the S meter at the other end...