I have optimized the dimensions of several types of collinears using simulation softwares 4nec2.
Using the optimized dimensions, I fabricated these collinears, and put to trial run. ALL BUILDS (MORE THAN A DOZEN) PROVED HOPELESS, much inferior to a 1/4 quarterwave groundplane antenna (Cantenna/Spider).
These designs included coaxial collinear (coco), wire collinears with coils between sections, wire collinears with stubs between sections, super Jpole etc. For ALL these designs, the simulation software gave optimized dimensions which should give a gain between 3.5dBi and 5.5 dBi and SWR between 1.5 and 1.1, but trial runs proved these to be completely wrong. Why? There is an error of about 5% to 10% in simulations output. This error is too much for a collinear, which is very intolerant to dimensional errors, and knocks it off far from tuning point if errors are as high as 5% to 10%.
Although the simulation software are not suitable to design a collinear for constrution purposes, these do give a very good picture of the performance of a design for understanding the general behaviour. I have therefore run a simulation, in which the 4nec2 software has varied the length of radials in steps of 1mm from 30mm to 285mm, and plotted results in the form of a graph.
The conclusion is that:
SWR: 1/4 & 3/4 wavelength radials give best SWR (1.91 & 1.65), 1/2 wavelength radials give worst SWR (13).
GAIN: 1/4 wavelength radials give better Gain (1.2 dBi) than 3/4 wavelength radials Gain (0.52 dBi). The 1/2 wavelength radial gives very poor gain (-12 dBi).
**These simulation results needs to be verified by trial runs. **
I plan to put on trial run a 1/4 monopole like the one in first post, but with 3/4 wavelength (203 mm) radials, run for 20 minutes, then trim the radials to 1/2 wavelength (138 mm), run again for 20 minutes, then again trim the radials to 1/4 wavelength (69mm) and run for another 20 minutes, and compare performance on performance graphs.
Will repeat above trial run, but this time with slanting (45 degrees) radials.
… Will keep me busy next weekend.