[Elecraft] BL-2 Balun Heating

[Steve Ellington]

I have the AT1KM. It has a nice big 4:1 balun built in. Have you tried it to
see if it gets hot too? That little BL2 may be rated for 250 watts but this
is for a resistive load or 200 ohms. It's not going to be able to handle the
extreme reactance of that antenna system. Even 25 watts would be asking a
lot of it.
I quote the BL2 manual:
"Power Rating 250 watts with a MATCHED LOAD". Your load is far from matched.
73

Steve
N4LQ
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Ron D'Eau Claire" <ron at cobi.biz>
To: <n2um at live.com>; <elecraft at mailman.qth.net>
Sent: Thursday, November 19, 2009 11:32 PM
Subject: Re: [Elecraft] BL-2 Balun Heating


> 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
>
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