[TenTec] Problem on 160 meters, Whats up?

[Dr. Gerald N. Johnson]

On Wed, 2009-03-18 at 18:54 -0700, Jim Brown wrote:
> d.e.warnick at comcast.net wrote:
> > The problem of heating an unmatched balun is one of the reasons that I chose the Palstar AT5K. 
> Heating in a common mode choke (current balun) has NOTHING to do with 
> SWR, it's all about antenna BALANCE, the common mode voltage across the 
> choke, and the choking impedance. If the choking impedance is high 
> enough, there's very little heating because there's very little current, 
> and power is I squared R!

Yet, just like a transformer, the voltage across the choke is the same
as the voltage on one side of the transformer, and one has to watch out
for core saturation. Higher permeability cores can saturate easier, but
the voltage for saturation is higher on the choke because there is only
one turn and the core cross section is greater. Yet that one turn also
limits the amount of inductance available to limit the magnetization
current.
> 
> Heating in a voltage balun (transformer) has little to do with SWR 
> either. All the TX power must go through the core. If the core is lossy 
> it gets hot. Period.

If the SWR is high and presents a high impedance at the voltage balun,
the voltage is high and so the magnetization current is high possibly
causing core saturation and then the magnetization inductance falls from
saturation and the current leaps (probably not a simple sine wave) and
the core heats drastically which also changes the limited permeability
leading to more heating and possible destruction of the core.
> 
> 73,
> 
> Jim Brown K9YC
> 
> _______________________________________________
73, Jerry, K0CQ