Topband: Core for K9AY loop transformer

[Joe Subich, W4TV]

Jim wrote: 

> Consider a suppressor on a wire shorter than a quarter wave. 

and 

> Above resonance, the choke will look capacitive, so it will 
> combine with the inductive reactance of a wire longer 
> than a quarter wave to reduce the total impedance, thus 
> increasing the current. 

Be careful of over simplification.  Because feedlines can 
(and often are) several wavelengths long (particularly on 
the higher bands), you need to specify ranges here.  Once 
the line is longer than 1/4 wave ... any line shorter than 
an odd multiple of one-eighth wave will be capacitive 
while a line longer than an odd multiple of one-eighth wave 
will be inductive.  

As the line reaches an odd quarter wave the reactive part of 
the impedance will move through 0 ohms and the real impedance 
will be relatively low - at this point lower impedance chokes 
(1 K or so) will be relatively more effective.  As the line 
reaches an EVEN quarter wave the reactive part of the impedance 
will also move through 0 ohms but the real part of the impedance 
will be quite high - at this point common mode chokes may be 
ineffective because they lack sufficient impedance.  

73, 

   ... Joe, W4TV