[Elecraft] RFIth

[Jim Brown]

On 12/20/2021 6:21 PM, Pete Smith N4ZR wrote:
> Others can speak more authoritatively about this, but I thought those 
> clamp-on cores, where they go right on the existing run of coax, offered 
> too little inductance to be of much use below VHF.  Experts?

That's right, sort of. But it misses the principle of how ferrite chokes 
work. It's NOT the inductance, it's the resonance formed by the parallel 
resonant circuit of series inductance and resistance coupled from the 
core with stray (parasitic) capacitance of the winding. Choking action 
is provided by the resistance associated with that parallel resonance. 
The most useful chokes are those with a broad, low Q resonance. THAT'S 
what is so special about the #31 mix, which combines the resonance of 
the winding with a dimensional resonance within the core. OTs among us 
will remember stagger-tuned IFs. Same principle.

k9yc.com/RFI-Ham.pdf  includes a tutorial discussion of this, so I won't 
repeat it here.

73, Jim K9YC