[TowerTalk] 4 square for 80

[Jim Brown]

On Mon,9/26/2016 7:41 AM, Rik van Riel wrote:
> The thing about resistive common mode chokes is, the higher
> their impedance, the lower the amount of power lost.

Right.

> Put a choke with over 1000 ohms of impedance into an antenna
> system with 35 ohm impedance, and the losses will be quite
> small.

Wrong. Power dissipated in the choke will depend on its resistive 
impedance and how it relates to the common mode circuit. That can be a 
very complex calculation. Also, the 35 ohm number you're citing has 
little to do with the calculation -- it's in the DIFFERENTIAL circuit.  
Several years ago, N2IC posted a question (maybe here) about power 
handling and dissipation for a choke. I didn't pay enough attention to 
his application and gave him a bad answer, which W8JI caught.

AND how much common mode power a given choke can dissipate depends a lot 
on its thermal mass and its ability to shed that heat to the 
environment.  A choke wound with RG8/213 size coax on five - six 2.4-in 
diameter #31 cores has a lot more thermal mass that a choke bifilar 
wound with #12 on a single #31 core, so the physically larger choke will 
handle more power than the smaller one, even if both have the same 
common mode impedance.

73, Jim K9YC