The SHORTYFORTY compact dipole for 40m band


 

You don't have the space to put up a full-size dipole for 40m ? No problems ... here comes the SHORTYFORTY !

Construction of antenna:

This antenna is quite critical, so it is important to construct is with utmost care, especially regarding symmetry ! In general, what 'looks nice' will work very well !

2x 20,5 turns of 2.5mm˛ ordinary copper wire PVC insulated on PVC tube (resistant to heat, 3mm thick wall) dia 50mm

In the centre, flatten the tube with a file to position the SO-239 connector.

Start the 4 windings quite wide, this because you will have to connect the feed. Make them absolutely symmetrical!

Detail of the SO-239 connector. It is riveted, the copperwire is fixed with solder lugs, which are soldered to the connector for a perfect connection. You see the tap at 2 turns, this gave the best SWR (about 1.2).

Windings are kept in position with PVC glue (preferably the 'hard type')

Inside of the tube, you see the small hookup wire going from centre of SO-239 to the 2nd winding.

Before affixing the SO-239, prepare this wire and insulate with heat shrink tube to protect against moisture

Then, with long nosed pliers, insert through hole you drilled next to second winding

Detail of connection to dipole wire, which is flexible copperwire 2.5mm˛ PVC coated, each arm 4m53 long (cut at least 20 cm longer to trim for your construction!)

Use crimp lugs which you solder and cover with heat shrink tube. Apply grease/vaseline to hardware (M5 bolt / nut / grower)

When everything is ready and tested, protect the coil with coating (I use a spray for car body protection - it is flexible and resistant to UV light
The completed antenna, only 9m40 long about

As the centre coil is quite heavy, I recommend to feed it with RG-58 instead of RG-213