[TenTec] [Fwd: Line Isolator Balun (sorta) question.]

[Steve Hunt]

It's actually short of an electrical half-wavelength, which gives it 
about 300 ohms of series capacitive reactance. That reactance is then 
cancelled by the inductive CM choke, leading to a lower CM path 
impedance and increased braid current. The effect is most noticeable, 
not when the braid is an electrical half-wavelength and the CM path 
impedance is lowest, but when it has a significant reactive component 
which may be offset by the choke impedance.

Even with 16ft of coax a Reactive choke will increase the braid current; 
albeit the current is low to begin with.

The point is that most operators will never know what their braid 
impedance will be; and it will likely be very different on different 
bands. So the safe option is a CM choke with a high RESISTIVE impedance.

73,
Steve G3TXQ


Dr. Gerald N. Johnson wrote:
> Of course there's lots of current in the braid, you made it nearly a 
> half wave long. Try the same experiment with that braid 16 feet long and 
> you will find much less current because then its a quarter wave long 
> terminated in a low impedance.
>
> 73, Jerry, K0CQ
>