I loosely assembled the antenna and took a few pictures. I'll do a final assembly in the next week and start testing this baby!
This antenna is a true, center fed, vertical dipole touted as having a 99.9% efficiency. The main elements are shortened and loaded (T-Bars) at both the top and bottom to give you a 50ohm feedpoint, yet still be resonant at the desired frequency. The entire radiating element is only 9+ feet long! The base insulator and base pipe make the whole assembly just under 12' total!
The manual says, "The feedpoint on the anenna is elevated, thereby adding to the performance by slightly lowering the take-off angle and having less current in the lower portion of the antenna in proximity to the ground. Later in the manual is also says, "The Sigma-11 should not be placed too high above the ground. If vertical antennas are placed too high, the energy splits off and creates a high angle lobe that actually has more energy than the desired low angle lobe."
Now, before anyone starts having a tizzy fit, remember that this antenna is NOT a ground plane antenna. It is a true vertical dipole which "provides a BALANCED vertical vs. having a vertical radiator and radials."
This antenna was designed to work close to the ground. I will do tests from 4' to 40' in the near future. The manual also includes plots of different heights....
Distance to lower T-BAR / Take Off Angle
4' / 18 degrees
12' / 13 degrees
This antenna sounds like a natural for those looking to hide one in the back yard. At just under 12' over all (including base pipe), it could be placed in a back yard and kept out of site very easily!
Here are a few initial thoughts:
Mechanical-
This thing is built like a tank! It uses 2" 6061 T6 aluminum with a .058" wall on the top 3 sections. The bottom 4th section, and the bottom support pole is .125" wall approx. The top and bottom T-Bars are 1" tapering to a 7/8" tube at approx 36" overall each.
The center and base insulator are made of SOLID 1.750" OD fiberglass. The upper 3 elements are swagged to mate with each other and the fiberglass insulators.
There is no worry of mixing up which tube fits where. An engraver was used to etch letters in the tubing. Match the lettes and you are set.
The T-Bar brackets were pre-assembled from the factory.
The T-Bars are pop-riveted together. There appears to be no rhyme or reason where the holes were drilled however. Still, you get three pop-rivet per joint!
You will notice that the balun (ferrite on RG-8X) has a support rod to hold it out away from the antenna. The manual suggests that you come down from the feedpoint at a 45 degree angle in order to prevent energy from coupling into the feedline.
It is a solid antenna that takes advantage of swagged elements in order to use one size of tubing. There has been many discussions about "capture area" and broader band widths using larger diameter elements. This antenna, at 2" in diameter, should make those trumpeters very happy!
I haven't put any juice to this antenna yet, but when I do, I'll let you know.
Now for the pictures:
http://www.worldwidedx.com/gallery/Force_12_Sigma_11?page=1
This antenna is a true, center fed, vertical dipole touted as having a 99.9% efficiency. The main elements are shortened and loaded (T-Bars) at both the top and bottom to give you a 50ohm feedpoint, yet still be resonant at the desired frequency. The entire radiating element is only 9+ feet long! The base insulator and base pipe make the whole assembly just under 12' total!
The manual says, "The feedpoint on the anenna is elevated, thereby adding to the performance by slightly lowering the take-off angle and having less current in the lower portion of the antenna in proximity to the ground. Later in the manual is also says, "The Sigma-11 should not be placed too high above the ground. If vertical antennas are placed too high, the energy splits off and creates a high angle lobe that actually has more energy than the desired low angle lobe."
Now, before anyone starts having a tizzy fit, remember that this antenna is NOT a ground plane antenna. It is a true vertical dipole which "provides a BALANCED vertical vs. having a vertical radiator and radials."
This antenna was designed to work close to the ground. I will do tests from 4' to 40' in the near future. The manual also includes plots of different heights....
Distance to lower T-BAR / Take Off Angle
4' / 18 degrees
12' / 13 degrees
This antenna sounds like a natural for those looking to hide one in the back yard. At just under 12' over all (including base pipe), it could be placed in a back yard and kept out of site very easily!
Here are a few initial thoughts:
Mechanical-
This thing is built like a tank! It uses 2" 6061 T6 aluminum with a .058" wall on the top 3 sections. The bottom 4th section, and the bottom support pole is .125" wall approx. The top and bottom T-Bars are 1" tapering to a 7/8" tube at approx 36" overall each.
The center and base insulator are made of SOLID 1.750" OD fiberglass. The upper 3 elements are swagged to mate with each other and the fiberglass insulators.
There is no worry of mixing up which tube fits where. An engraver was used to etch letters in the tubing. Match the lettes and you are set.
The T-Bar brackets were pre-assembled from the factory.
The T-Bars are pop-riveted together. There appears to be no rhyme or reason where the holes were drilled however. Still, you get three pop-rivet per joint!
You will notice that the balun (ferrite on RG-8X) has a support rod to hold it out away from the antenna. The manual suggests that you come down from the feedpoint at a 45 degree angle in order to prevent energy from coupling into the feedline.
It is a solid antenna that takes advantage of swagged elements in order to use one size of tubing. There has been many discussions about "capture area" and broader band widths using larger diameter elements. This antenna, at 2" in diameter, should make those trumpeters very happy!
I haven't put any juice to this antenna yet, but when I do, I'll let you know.
Now for the pictures:
http://www.worldwidedx.com/gallery/Force_12_Sigma_11?page=1
