http://elecraft.85.s1.nabble.com/Re-NOT-the-feedline-was-KPA-1500-faulting-on-6m-SWR-issues-tp7661502p7661555.html
folded dipole made of equal wire diameter or size. Depending on height
4:1 give an impedance of 50 to 75 ohms. Any other usage of a 4:1
> On 6/1/2020 6:45 AM, Alan - G4GNX wrote:
>> I have a similar issue with ferrite 'balun' heating, although mostly
>> tested on 40 metres. I'm using an OSCFD (Windom) which has a main 4:1
>> balun at the feed point, but also has a sleeve 'balun' consisting of
>> 8 ferrites wrapped in a plastic sleeve, about 3 feet from the feed
>> point. If I run the K3S at 100W, via the KPA500 in standby, then
>> through the KAT500 tuner, I see no problems.
>>
>> On increasing the power to 200W by using the KPA500 in Operate and
>> about 10W drive from the K3S, during a SSB 'over' the temperature of
>> the KPA500 rises and after a few minutes, the SWR readings on the
>> KPA500 and KAT500 start to rise.
>
> Alan,
>
> What you describe basically a lousy common mode choke, applied to an
> antenna that, because it is so badly unbalanced, has a LOT common mode
> current. The primary function of such a choke is to prevent common
> mode noise picked up on that feedline from coupling to the antenna,
> and from there to the receiver. I don't know of a way to EFFECTIVELY
> choke such an antenna. The application of ANY choke to such an antenna
> is an unnatural act -- it does nothing useful.
>
> I strongly suggest that you study the material on my website about how
> common mode chokes work. These concepts have been part of the ARRL
> Handbook and/or Antenna Book for nearly 10 years.
>
> k9yc.com/publish.htm
>
> The word "balun" is used to describe nearly a dozen very different
> things. What COULD work is a two winding transformer wound on a low
> loss ferrite toroid, like Fair-Rite #61 or #67 material. #61 will
> likely handle 100W from 160M to 10M without overheating. #67, which
> has much lower loss above about 17M, may be required at the 400W
> level, and would certainly be used at 1 kW and above.
>
> Making the windings bifilar provides a capacitive path for common mode
> current, degrading its effectiveness. This is minimized by placing the
> windings on opposite sides of the toroidal core.
>
> 73, Jim K9YC
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