[Elecraft] BL-2 Balun Heating

[Ron D'Eau Claire]

Yes, you are reaching the "curie temperature" of the core. At that point
it's magnetic properties change dramatically. 

Of course that heat comes from RF that is becoming heat instead of being
radiated by the antenna. A bigger core isn't the answer. You'd still be
losing the same amount of power even if a much larger core felt cooler. Same
with a heat sink.

You didn't say what band you are using. Heating a balun is usually a sign of
excessive current flowing -that is you are at a current loop. You can change
that by changing the length of the feedline or just do away with the balun
and connect one side of the open wire feeders to the center pin of the tuner
output and the other to the case. That does not introduce anything like the
degree of "unbalance" that some suggest. Indeed, the balance in the feedline
is much more strongly affected by the antenna than the source. 

Ron AC7AC


-----Original Message-----
I recently built a BL-2 Balun.  It is connected between my Palstar AT1KM 
tuner and my doublet antenna.  The antenna consists of a 100' wire up 
25' and fed by 95' of 600 ohm open wire feeder.  I'm using the 1:1 
setting on the balun.  There is a 4" section of RG-213 between the balun 
and a coax input of the tuner.  I'm driving it with 125 watts from a 
TS-850.   After no more than a few minutes of CW or RTTY transmission, 
the balun is too hot to touch, the SWR rises and the power goes down.  
The balun is obviously saturated. 

Does anyone have an idea how I can reduce the overheating?  I've tried 
adding a heat sink but it doesn't make any difference.

Tnx for reading!

Gary  N2UM