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This is another of Dr. Jerry Sevick's (W2FMI) most popular designs modified with various connector configurations. This model is much more than just high power. The specs are equivilant to the Model 1115u 5kw Isolation Balun but designed for easy installation with yagis, 1/2 wave dipoles or designs that work best with studs mounted on the sides of the enclosure. By using our mounting plate or mounting clamp, the balun can be securely installed on a mast or boom.
Specifications are very impressive. Using an AIM-4170 for testing, the balun shows an SWR below 1.06 across the entire HF band, literally flat transformation, and return loss that averages 60-75 dbmw. You can view these results in the graphs below.
This is a current balun and has the widest operating frequency range, lowest core stress and provides the best overall balance of any balun for given cost, size, and weight. This balun is the best type to balance currents on each side of a 1/2 wave dipole or the driven element of a yagi while providing the perfect transition from a balanced antenna to unbalanced coax feedline.
Installing this balun will not affect antenna matching unless the feedline is acting as part of the antenna. This of course, is not a desirable situation and installing this balun will correct the problem if one exists with the antenna. In beam installations, using a 1:1 balun in series with the antenna’s feed system can substantially improve the antenna’s front-to-back and front-to-side ratios. It does this by providing the antenna's driven elements with balanced current at the feedpoint and by preventing the feedline from acting as part of the antenna.
It is a seldom appreciated fact that feedlines, which are not adequately decoupled, can act as efficient vertical antennas degrading an otherwise excellent radiation pattern. The addition of a 1:1 balun can significantly reduce feedline radiation and dramatically decrease RFI and TVI. Beam antennas especially benefit from improved balanced drive andsuperior feedline isolation, but even simple dipoles benefit from properly selected and installed 1:1 current baluns. Receiver noise is also reduced by eliminating EMI and other signals picked up by the coax shield.
Here are plots of the same dipole with and without a balun, notice how the pattern is distorted when the feedline is not being isolated with a balun:
One Exception!!! Also, please note that although this balun will tolerate very high SWR, efficiency drops markedly if your SWR is 4:1 or above.
Design features:
This balun will handle continuous power of 5kw or 10kw intermittent and tolerate high SWR for extended periods. It will not heat up at rated power, extended duty cycles or stressing load conditions.
You can see from the pictures there are three versions. One with closed eye loops to provide anchors for dipoles or with studs on the sides for mounting on a mast or other support. The balun can also be built with studs on top of the enclosure for use with yagis or applications that require this design. A closed loop in the accessories section can also be added to the top of the enclosure as a hanging support.
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