04 December 2013

W3EDP Antenna

After a major hail storm here my end-fed halfwave was destroyed. A good time to try a different antenna! A version of the ancient W3EDP antenna was published in the South African QRP handbook. See the attached schematic of this famous multi-band antenna.

I built the 40 m coupler into an exterior light fitting. This fitting is inexpensive at R30 from the hardware store down the road. The 'cabinet' is waterproof and also has breather holes on the bottom. The 265pf capacitor is mounted with the shaft facing downwards. The tuning coil was wound on a 50mm piece of PVC pipe.

A small stand was built to support the coupler. This stand allows me to deploy the unit on the lawn. It can easily be removed or moved around in order to prevent the grass dying under it.

The 84ft wire has a vertical section of approx 20ft long and is supported by two trees at each end. The horizontal section is close to horizontal to the ground and about 20ft high.

The coupler tuned to resonance at the predicted L/C combination on 40m. With the counterpoise strung out across the top of the flowers in the flowerbed and about 4ft off the ground, I was able to tweek the link winding to a position on the coil in such a way as to achieve a perfect 1:1 match on 7020KHz. In fact the antenna displays a reasonably low Q and thus it is possible to work the whole 40m band with an SWR below 1.7:1. The inductor measured 2.082uH on my LC meter using 7Turns.

The coupler is connected via a coax cable of about 70ft back to the shack.

So far after a few days of operation I have received reasonable reports from local stations. Clearly the antenna is mainly an NVIS local antenna, however I am able to hear DX quite clearly. The high sunspot activity at the moment no doubt is assisting.

Moving the counterpoise to lie on the ground certainly brings the SWR up. Further tweeking of the link coupling would be required to achieve a low SWR.

Reading the literature it appears that the W3EDP can be argued as a type of end fed Zepp. Better performance may be obtained by turning the 'counterpoise' into a balanced feeder line. This then becomes a 66ft end fed wire with a transmission line matching section....

Well I like the idea of deploying the traditional and original W3EDP better!

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