Hello Henry,
I did find the collinear antenna in the storage unit but unfortunately it got beat up pretty bad after I lost interest in it. The working prototype only succeeds in adding an additional in phase 1/2 wave to the existing 3/4 wave and falls short of adding 3db as a result. The last phasing coil I used was literally taped across the insulator and fell off over the years. I found it flat underneath a pallet of boxes!
I thought I could just measure that coil but then I found the alligator clip and short wire that I used to tap the coil in the spot that produced the best gain. Needless to say that tap point was lost. What is not lost is my memory of how it works or ability to explain it in a way that is reproducible. Although, I am surprised that I've not been able to get anyone to build a model as I described.
It really is very simple. Take a stock Sigma or Vector model in EZNEC. Imagine we attach a 2 or 3 inch insulator right at the top of this antenna. Add one horizontal wire extending to the left from the bottom of the insulator that connects to the top of the existing antenna. According to EZNEC this wire should be about 1/4 wavelength or just over 8 feet on this band.
At the far open left end of this new horizontal 1/4 wave wire, connect a second upward, vertical wire the same length as the 2 or 3 inch insulator. From the top of this short vertical wire connect a 3rd wire that is horizontal, extending to the right and parallel to the first horizontal 1/4 wave wire you added. The open end should now be inline with the top of the insulator. You have just formed a 1/4 wave shorted phasing stub. The overall phase shift through both legs of this stub will be delayed 180 degrees.
From the top of this insulator connect a 1/2 wave vertical wire to the top of the phasing stub to form the top 1/2 wave collinear element. Run the average gain test. With a little tweaking of both vertical radiator lengths and the phasing stub you might see a maximum of 1.5 or 1.7db over the stock antenna in this program.
Now we need to test these model results in the field. The easiest way to do that is to let EZNEC rescale the antenna for 2 meters then build it. The antenna will tune up and work fine before you add the insulator, phasing stub and top 1/2 wave. As soon as you do that the reactance and match go out the window. Lots of retuning the gamma can bring the VSWR down but there is no gain over the stock antenna and some loss could be detected through the match.
Just before you give up on getting this to work in the field do something crazy. Eyeball the length of the phasing stub to find the mid point and cut it right in half! Then attach the small shorting bar back across the open end of the stub and watch the antenna start to work in the field. You'll also notice that you can remove the entire top of the antenna from the stub up and not upset the match. Exactly how we expect a properly tuned collinear to operate.
This collinear antenna only needs a 90 degree phase delay since the first 1/4 wave driven from the feedpoint has already been confined inside the cone and effectively "delayed" within it. Remember a phasing section on a collinear antenna merely has to provide a means of minimizing radiation at a key point on these longer antennas were the currents become deconstructive. That condition exists inside the cone. It doesn't have to look conventional to the eye and can be rather "non apparent" as in this case.
If the outside or 3rd conductor on the cone was not radiating a significant in phase current, what EZNEC predicts about the 180 degree phase delay would still work in the field. The fact that the only phase delay that can make another 1/2 wave fall into phase with the radiation below it is a 90 degree shift, proves there is another significant in phase current other than the original 1/2 wave extending above the cone. It also supports that the wavelength of that second radiated current must be the 90 degree 1/4 wave outside surface of the cone.
Funny thing is if you now take what you learned in the field and apply it in EZNEC with the working 90 degree phase delay, you find the EZNEC results here will be just as messed up as the program results proved to be in the field. All of this together supports my conclusion that no EZNEC model has ever displayed an accurate analysis of the Sigma design. I've presented this information everywhere from forums to Roy who wrote the EZNEC programs. Roy told me the program was not capable of miscalculating any radiation currents and that the error must be in my phase delay measurements.
To me that translated into "I don't know and I don't care" because it's a slim chance that I failed to take the measurements from his software and miss them on the tape measure by making them 100% longer. It's an insult to suggest that one can't tell 4 feet from 8 feet on the Stanley or read the numbers printed on the software screen. Many of you have probably seen me rant about all of this before and I apologize for being redundant, but at the same time there are people here interested in why the common model can't show what field tests and CST do.
Admittedly, the time I could invest in this research hinged on the profitability of the project. Because the results proved the antenna was an in phase 3/4 wave radiator, adding another single collinear section could never double the existing gain. One night I found myself going over the list of improvements required on the prototypes before they could go into production. We were dealing with everything from reduced bandwidth and power handling to weather detuning the phasing stub and wind casing undesired mechanical beam tilt on the long antenna.
All that work and added expenses to manufacture something of commercial grade and for a measly 1.5db? It was clear the most effective and economical way to add gain here was to add more antennas mounted and fed in phase. That's how you get close to the full 3db gain every time you double the number of antennas and has been a proven method for over half a century.
