Efficient Half Size Dipole for 40 meters

In my continuing saga of antenna experiments, I have designed  a 30 (a little less than 1/2 normal size) foot long 40 meter dipole that is a solid performer. The goal was to make it short enough that it would work well in portable applications as a vertical or sloper hung from a tree.  It is center fed with one continuous loading coil tapped at the center two turns to a SO-239 type jack for coax. A balun is not necessary because of  the tapped connection to the loading coil. Along with the loading coil, there are two cylindrical capacitive hats which  replace about six  feet of wire each. The hats improve current distribution, bandwidth and efficiency,  allowing for a smaller loading coil. The hats are lightweight and flatten out for very easy transport. The antenna uses carabiners and inline connectors to allow quick connect and disconnect for setup and removal.

Link To STL Files

https://www.adrive.com/public/F8Fsz4/Antenna%20Forms.zip

Antenna mounted as a sloper

IMG_20151031_165712056

The Loading Coil and Hat frames were printed on my 3D printer using a low RF loss plastic material – High Impact Polystyrene(HIPS). Here is a link to the STL files which can be used to print these forms. An STL file is the standard format used by almost all 3D printers. If you do not have a 3D printer – there are online services available to 3D print the files as well as some print shops and office stores. Other plastics could be used such as ABS but use HIPS if you can. Because the antenna is relatively small you can mount it vertically or nearly vertical with the center relatively high above ground for better efficiency so besides being small, the antenna has some benefits with respect to ground losses and radiation angle (depending on how you mount it).

Loading Coil

Coil has 11 full turns(plus half a turn) to center from each side(3 inch diameter and 3/16ths turn spacing). It can use 12 gauge or smaller wire. The mounting holes can be tapped for 6/32 or 8/32 screws for the coil terminal and connector flange. Total coil inductance between 16-17 uH

IMG_20151031_170006399 IMG_20151031_165858898

Capacitive Hat

The hats are 6 inches in diameter with the wire soldered together in the center and then pinned with a 8/32 screw and washer.

IMG_20151031_165650532

Antenna adjusted to resonance for 40 meter CW

IMG_20151031_170252197

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2 thoughts on “Efficient Half Size Dipole for 40 meters

    • oh yes results have been good. As a sloper it works fine. I have been getting the best results just getting it 30 feet up in the air…which not to hard since it is short. Typically get 559 reports with 1 watt best contact was Idaho (3000 miles) but mostly get 500 mile up to 1k contacts. I am in North Carolina

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