On 2009-09-24, Tomylavitesse wrote:
HI,

Often I can see coils where some turns are shorted in order to modify there
value.
I wonder whether these shorted turns would not be seen as a short cicuit and
could decrease the quality of that coil.
How can I have an idea of the lost of quality without complex equipment ?
I plan to build this kind of coil for a shortened antenna...

The circuit to shorten turns in such environments has to be very low
loss. Otherwise you will have lots of power lost in this short
circiuted parts of the coil. And in PA / antenna environments you
always have power. This is why switches are always "heavy duty" in PA
and antenna switching units.

If you do so, the current in this shortened turns is a complex
current. And as you know, complex currents do not consume power. Only
the real parts of current do.

This is totally different from the situation e.g. in a power
transformator. If you would shorten turns there, you would have power
loss, because the resistant of the turns in power transformators has a
much higher real part compared with rf coils in PA / antenna units.

OK?