Over the last two weeks, I was able to complete my phased 40m vertical project. My original plan was to use the standard, 90 degree spacing, fed 90 degrees out of phase. I discovered the day after setting the 2nd vertical base that the house next to mine would be occupied. Since this 2nd vertical would be quite close to the house, I decided to rethink the array, going with 1/8 wave spacing fed 135 degrees out of phase. Gain figures are similar, however the lower feed point impedances you get with close spaced verticals means ground losses are amplified. 2 ohms of ground loss means a lot more when your feed point impedance is 15 ohms vice the standard 36 ohms, when efficiency is taken into consideration.
In my case, I placed the verticals in a N/S configuration. The beamwidth is wide enough to cover both Europe and North America. They are fed using standard published figures for the Christman Method of phasing – 157 degree delay lines to each vertical with a 39 degree delay line to create the phase shift. In my case, the actual numbers needed may differ, however I don’t have an accurate enough method of measuring complex impedances so I went with the standard values.
Under each vertical are at least 40 radials (the older vertical has more). The white PVC sleeves the lower section of both verticals for safety reasons. My new neigbor has a toddler who likes to run around the back yard, including mine. The PVC increases visibility and should allow him to bounce right off the antenna uninjured should he run into it.
The below photo shows the switching relays. I built them into a Home Depot outlet box. There are no Radio Shacks here – and I don’t want to wait two weeks for a Mouser order to arrive. I’ve found that it is nearly impossible to keep water out of an enclosure, so I don’t worry about it. The stamped box works fine for shielding, and a bucket over the whole thing keeps the box and coax connectors out of the rain. The center relay is used to switch between the North and South positions, and the relay to the right in the photo shorts out the delay line for omnidirectional (theoretical 0.3db gain to the East and West).
How does it work? I won’t really know until the Oceania DX contest. Over the past year, I had a single vertical and a dipole. At no times was any antenna better than the other. I have to assume the 2nd vertical gives me something – even if less than nominal gain – unless I have serious ground loss issues which I don’t think I have. There is some interaction with the Spiderbeam mast. I see big F/B (24dB) on 4W6A who is almost South of me, but little change on stations to the North. My QSL manager, W2YC, seems to think I’m about 1/2 S-unit louder in the north position which does back the theoretical 3dB gain figure.