Topband: Balun Discussions

[i4jmy at iol.it]

Nobody told that beyond the resonance the choke impedance goes further increasing, of course it doesn't because of inductor self capacitance. 
Disregarding self capacitance, which is a parasitic effect anyway, and very little felt on topband, the inductor reactance is multiplied by four when doubling the number of turns. 

The only way to have more reactance in real life chokes is to work in the around of an inductor self reasonance, whose thing is obtained acting with the number of turns, if and when inter-wire capacitance is a fixed value.

Self capacitance anyway, is a matter of capacitance between adiacent turns, and in a single layer coil it doesn't add for increasing the number of turns. 

Talking about 1.8 MHz it's uncommon to go beyond resonance with common coil sizes and standard RG213 lines. The warning to have an excessive number of turns is a purely academic speech with a little practical application.

Chokes, moreover, out of the TEM mode which is confined inside, are not lines and do not behave like lines. In the "outside" of the choke, there is one, and only one, self resonance.

73 & HNY
Mauri I4JMY


> 
> The trend stops rather quickly and it is easy
> to have too many turns on higher bands.
> 
> After parallel resonance is reached impedance drops.
> 
> Baluns and other chokes are used in the frequency
> region well above one where they can be regarded as
> simple inductors. Chokes are transmission lines.
> Impedance rises and falls periodically with
> increasing length.
> 
> 
> 73,
> 
> Sinisa  YT1NT, VA3TTN