My experience is that the Balun-Designs 4:1 current balun works
brilliantly on a well designed ocf antenna with decent height and
proportions to
provide good band sync at the same impedance point, where the different
band sine waves intersect, at the approx 1/3 total length feedpoint.
shown in below from ;
https://archive.org/details/UnderstandingAndBuildingTheOCFDipole
However these days I use delta loops, beams and verticals.
Adrian Fewster
On 2/6/20 1:01 pm, Bob McGraw K4TAX wrote:
I agree with Jim, K9YC on these points.
** OCFD antennas are noted to have lots of common mode current
issues. These are a chore to tame.
** Most commercial baluns or common mode chokes are poor designs, of
inadequate material, designs copied from other poor designs but packed
in a pretty box of different color, size, and shape with a high price.
One of the best applications for a 4:1 balun is with a single band
folded dipole made of equal wire diameter or size. Depending on height
above ground the feed point Z is between 200 and 300 ohms. The use of
a 4:1 give an impedance of 50 to 75 ohms. Any other usage of a 4:1
balun is more of a compromise to a disaster.
73
Bob, K4TAX
On 6/1/2020 9:41 PM, Jim Brown wrote:
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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
