Home: https://ky8d.net/spiral
Series:
[1]
[2]
[3]
[4]
[5]
Iteration Set #4: So far as yet, performance for the 12m band is decidedly lacking. Why? I'm not sure. One option yet left to try is reducing outside diameter (governed by CLI arg 'f_lo'). This would, of course, harm to performance on the 20m band. Will that work and be worth it? Let's find out.
From a personal perspective, very much to be preferred is best peformance at the CW ends of contest-free WARC bands.
Color Key for Paragraph Text: White (greater contrast) presents information crucial to interpretation. Red presents a delving into various fiddly details about the surounding main text in white. Stuff which I feel some readers may find self-evident, uninteresting, or even beside-the-point. Tidbits I couldn't convince myself to simply delete.
Construction practicality would argue against a spiral resolution of div = 32. Far too many radii. This data set, therefor, is for information only, aimed at discovery of best compromise value of spiral outside diameter. Once discovered, I'll run further iterations for div = 16 and lower to see what I get.
Iterations Not Shown: For having iterated on f_lo with stp = 0.2 while div = 32, it frequently happened that consecutive antenna desings came out identical, requiring manual deleiton.
Periodically this happens. The cause is a design rule which enforces that spiral-wire ends must terminate at a support radius. Here the number of radii are governed by the criterion div = 32, which had priority over all else. Consequently, whatever was the value of for f_lo, this got superceded by the practical necessity of extending wire ends to meet the next radial intersection.
Obviously, all these spirals will be requireing open-wire feed lines and a tuner. This in trade for construction of much less wire. But as the goal is to obtain a wide-band spiral that might be fit on the skinny in between trees, certain trade-offs are to be expected.
I know what you're thinking. Why not a simple fan dipole? Why not nested loops? Wouldn't I save even more wire? I'll compare against both of those once I've narrowed down my spiral to a final design.
A spiral OD equivalent to lambda/2 for 16.1MHz clearly offers best gain on 17m, 15m, and 12m. This while still leaving some performance on 14m. Mitigating this loss, I now have antenna 2.14m smaller in its OD.
And now that it's smaller, construction complexity is maybe less of an issue. So now I am wondering whether or not I might get back some the gain lost to 20m by having gone smaller. Might this smaller antenna benefit enough fromIt is on the contest-free WARC bands where I prefer to hang out. So I should next iterate over div once again, this time with f_lo = 16.1, thus to discover how few radii might be got away with.
And so, that's what I'll try next: Re-Iterating on Div.