Model 1113et - 1:1 Isolation - Suppression Balun, 1.5-54 Mhz, 3kW KIT

The venerable 1:1 isolation/choke balun is the first of our new line of DIY kits.  All components are the same as those used in our pre-assembled units. This finished balun will have an SO-239 for input, two 1/4" eyebolts for wire elements and one eyebolt on top for support.  This configuration is typically used to feed a resonant dipole and provide strain relief for the wire elements.

This is a very easy, straight forward build and can be completed by anyone that has built any type of kit or soldered their own coax connectors.

Kit Instructions

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We're bring back one of Dr. Jerry Sevick's (W2FMI) original designs but with upgraded windings.  This balun was one of our original workhorses and now with new coaxial windings, provides a single core balun optimized for 40 - 10m.  By using our low permeability core, this balun provides excellent RF choking and feedline isolation at higher frequencies with lower loss and less heat generation. Excellent balun for RFI suppression on the upper bands, use at feepoint of multi band yagis running mid range power levels  and monoband resonant dipoles for 40m and above. Our model 1115d is the dual core, 5kW version of this balun.

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Testing done with an AIM-4170uhf Network Analyzer

 Please review our Accessories Category for additional RF connector types and mounting options.

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.

Of course, this 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 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 and superior feedline isolation, but even simple dipoles benefit from properly selected and installed 1:1 current baluns. Receiver noise may also be reduced by eliminating signal pickup by the coax shield.

Here are plots of the same dipole with and without a balun. 
Notice how the pattern is distorted without the feedline being isolated by the balun:

 
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*** One Exception ***

It must be pointed out that a 1:1 balun should never be used on the second harmonic of a half-wave center-fed dipole fed with coax (like an 80 meter dipole being used on 40 meters). The impedance can be as great as 5,000 ohms creating very high voltages which can bring about voltage breakdown and/or excessive heating. This exception ONLY applies to Coax Fed HALF WAVE CENTER FED DIPOLES WHEN USING A 1:1 BALUN AT THE FEEDPOINT.  This caution does not apply to fan dipoles or any dipole that utilizes loading coils to create resonance on the bands in use.

Specifications

Installation Notes