1:1 BalUn project

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There are many antennas available to purchase and one could spend days deciding on which one to use, but building your own antenna system I think is much more enjoyable and really not hard to do! After deciding to which one to build, an impedance matching device was needed to interface the antenna to the transmitter, the BalUn. A BalUn is used to electrically connect an Unbalanced feedline, such as coaxial cable to a Balanced antenna, such as a dipole.

KE6JZS under $30.00 BalUn project.

Kids, Please try this at home.

First was to decide what type of materials and housing to use. I chose to use PVC water pipe. I selected 4" for one and 2" for the other to enable me enough room on the inside to construct the coil needed.

PVC Tube Housing

KE6JZS_BalUn_1.JPG

After some internet research on BalUns I learned a coil was needed to form a transformer of such. I used Belden 9913 coaxial cable to construct the 4" BalUn coil and RG-58 to construct the smaller 2" BalUn. The length I used was 19' feet. A tight wound single layer coil was constructed on the inter diameter of both the 4" and 2" PVC pipe.

Single Layer Coil

Careful separation of the braid was taken to properly form the mirrored leg connection. Take your time, it's worth it to not have stray braids. KI6KNA had the patients to do this step.

Perpare Braiding

Here the braids were arranged and held in place with a light coat of solder. Then lugs were installed to attach them from the inside to the dipole leg posts.

Balanced End Connections

SPECIAL NOTE: The above photo shows the critical position of the dipole leg connections. I found I was not able to achevie an acceptable SWR untill I positioned the dipole leg connections up and out of the magnetic field of the coil. I used an arched form.

KE6JZS_BalUn_2.JPG

Now that the coil was in place, connections need to made. On the bottom of the the coil I installed a chassis mount N-Type connector which will late be mounted in the center of the bottom cap. The connections for the dipole were constructed using copper 1/4" 20 thread bolts, washers and nuts. The bolts were inserted in a strip of copper sheeting to form a copper tab then the heads of the bolts were soldered to the strips and inserted through the PVC pipe near the top of the coil. Be sure to leave room for the top cap! Secureing the bolts on the outside with a washer and another copper nut for locking.

Prepare Braiding for N-Type Connector

The same care should be taken here for preparing the braid.

Installed N-Type Connector

Mounted N-Type Connector

KE6JZS_BalUn_3.JPG

Next is to installed the top cap. In the center of the cap I drilled and installed a 1/4 " eye bolt. This enabled me to use a D-Ring, rope and pulley system to lower and make adjustments, then rasie it for operations.

2" Top Cap

Weather Proofed

Finished 2" Model

KE6JZS_BalUn_4.JPG

Install the bottom cap with a center installed N-Type chassis mount connector. Use a little RTV on the inside for weather proofing.

KE6JZS_BalUn_6.JPG

Below is the finished unit, modeled by KI6KNA. The whole project was completed in an afternoon. Nasa sticker was added to electrically gather more signal from the air. hehe.....

2" BalUn

4" Hi power BalUn

Now I simply cut to length 4 dipole legs, 80m, 40m, 20m and 10m, securing them with copper lugs and solder, hoisted them up the tower. With a little help from Bob KD6DYR and his MFJ antenna analyzer we manuvered the legs into usable VSWR positions.

KE6JZS_BalUn_7.JPG

A little hard to see by this shot, but there she is in all her glory! Multiband inverted-Vee. The whole project cost was under $30.00 and will probably be around for the next 100 years.

KE6JZS_BalUn_8.JPG

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