Bob: I did find the FM prototype however I've robbed many parts off it since I last tested the antenna. No gamma and the top sections are missing. I found the loop still mounted on the base. If you're interested in seeing what this looks like, drop me an email on my business website and I will forward it to you. I'm not sure how to post a picture here. The good news is if you wait a while, I am constructing another one for 11 meters. All this talk here has got me wanting to make the best one I can for 11. As an amateur operator for the last 15 years, believe it or not I still have more fun on 11. In fact I have a Vector 4000 on the roof now that I use on 10 and 11. Other then swapping out the gamma and UHF connector this antenna is stock.
I've already started the build on it's replacement and made the loop. The loop I decided on uses six of the stock loop pieces rather then four. They are overlapped by 3 inches on each end and double bolted together so they can't pivot. This makes the loop about a third larger then stock (minus the overlap). With the fixed loop size I will be able to slide the four support rods for the loop into the bottom sections and find the point of highest gain. It will definitely required four shorter support rods because of the larger loop. Thus, no extending of the rods will be needed.
I can't promise when I will have this completed since it competes for time with my business however, as soon as I can I would be glad to forward you the correct measurements. From my FM tests I can tell you that the best case scenario for this modification will add about 1 db to the stock antenna. That's a total of 3 db. Isn't it funny how many other CB antennas you can find on the market that advertise much more gain but still can't out perform the Sigma style? Other then the Sirio, I know of no other CB antenna manufacturer that uses real gain figures as compared to a dipole. Even Avanti lied claiming over 6 db although their patent told the truth.
Booty Monster: Just buy the Sirio from H&Y Electronics and follow the steps in my previous post that outline the slitting of the top sections and use of hose clamps. This nearly eliminates the top sections from breaking off. The original method of screwing the sections together sucks because there is too much clearance between the diameters of tubing. This play always causes wear in the tubing at the point where sections meet until they eventually break or strip out the screws.
The LW-150 was too long for maximum gain and used a fixed tap point on the main radiator for the gamma. This caused problems with tuning it up for a perfect VSWR. You could only adjust the capacitive reactance of the system with the gamma. In order to adjust the inductive component you were forced to take the antenna down and adjust the top whip length. The variable tap point on the Sirio and original Sigma makes them superior with respect to VSWR adjustment.
Sirio's new length around 28 feet is close to what I expect to use however, the ball at the top has to go. Silly idea that looks better then it works. The antenna is DC grounded so static buildup is not an issue the ball can help with. It may improve bandwidth the slightest bit but it's not worth installing. Mostly because it is a bird catcher. Sirio used this ball on top of their S-2000 5/8 wave first. I had one and the first time any bird larger then a Robbin or Barn Swallow landed on it, the top folder over as the bird jumped off. I saw this happen in front of my eyes and was quite disapointed. Removal of the ball will require adding a couple inches to the radiator to compensate.
