Figure 1: Graphic of relative signal strengths from my Delta loop (top apex feed) antenna.
So, I have been using the Delta loop for a while, perched at its new height of 55 ft, and have been measuring the results with different feed configurations. Initially, I had the corner feed (bottom) – with its resultant vertical polarization, and pretty good far-signal performance. Then, I tried a center-bottom feed, and finally a top (apex) feed. I have created some graphs to show the results so far (yellow numbers are signal db, and white markers are miles).
The top graphic shows the top (apex feed), and the second graphic shows the center-bottom feed. I was really surprised by the results, not so much by the fact that the bottom feed would be close to NVIS, but that the difference has so many nuances built into it. Look at the signal strengths in the second graphic for short range (<400 miles). They are significantly above *any* of the signals in the top-fed configuration.
Figure 2: Bottom-center fed delta loop
The first graphic shows the top-fed configuration, with much lengthier likely-qso paths. The highest db figures are more muted than for the bottom-center-fed antenna, but also go for a longer range. The db figures placed outside the bullseye are not even close to any kind of scale. The ones on the right are from Europe naturally.
The right side of the second graph is truncated by the ocean, of course, for the reason that the bottom feed was not reaching Europe. The broadside of the antenna is a few degrees north of west (towards the west) and a few degrees south of east (towards the east). So, there might be seen in the first graphic a perceptible null on the sides of the antenna (due north and due south). The stronger db values of the NVIS configuration (center-bottom feed) might be erasing the nulls.
Of course, the lengthier path configuration is spreading its power over a larger area, so the highest db readings are muted from what the more NVIS-ish (bottom-center-fed) configuration gives me. So, if I want to really blast a signal at the receivers of hams within 400 or 450 miles, then I would go with the center-bottom feed. If I want a more common-denominator sort of antenna, with probably much higher QSO-count capability that comes with a spread-out signal, then I would choose the apex (top) feed, or the corner feed. Due to the fact that we have poor ground conductivity, and the corner feed is vertically polarized, I’m sticking with the top feed as my choice.
Best 73’s – Ron / WB8LZR
WB8LZR 