Is the Sigma IV really a J-Pole?

[Master Chief]

try installing a physical 3/4 wave vertical radiating element over 3 or 4 1/4 wave (or slightly less) radial elements, connect an analyzer or noise bridge at the feedpoint and watch what happens when you sweep the radial elements upward to within 15 degrees of the bottom 1/4 wave section of the vertical element........

This can be done with software and make it a whole lot easier! Now I have a question; If the imports needed the extra 4' to resonate at 3/4 wave, then how did Avanti do it without the extra 4'?

Or are you saying that the Avanti IS a 1/2 wave and the imports are actually 3/4 wave and not a 5/8?

 

[freecell]

"If the imports needed the extra 4' to resonate at 3/4 wave, then how did Avanti do it without the extra 4'?"

actually the length in the Avanti was 27' 7". the major difference between the two was one more (or less) radial elements combined with other small measurement differences between competing models and with the divergent length to diameter ratios involved in the vertical element, particularly towards the top where in one was 1/2" tubing and in the other was something closer to a steel whip taper. each had their associated advantages and disadvantages from both electrical and mechanical perspectives.

i'm saying that the Avanti Sigma 4 and the majority of export copies like the lw150, saliut 27 and others are electrically 3/4 wavelength in performance.

even the I10K is a 3/4 wave antenna, speaking electrically and not physically. see my previous post on the 5/8 wave configuration.

 

[bob85]

freecell maybe i am missreading what your saying here but i can tell you that either basket will work on either the 27ft or 31ft radiator and the longer one works better for us, the leftovers from my buddies hybrid went to make a vector radiator 31ft with the original avanti 3 leg basket, it tunes ok works great and is still in use locally, another ham friend uses his original avanti extended to around 31ft on 10mtrs and claims better results with the extended radiator that i can see on his signal to me over 15 miles or so :?:

 

[bob85]

the only sigma copy that is over 27ft long over here is the vector 4000, all the others mentioned in this and other posts where around 27ft with either 3 or 4 legs

 

[freecell]

bob85,

understood.

the lw101 / serio linked to earlier at H&Y is also over 31 feet. (9500 mm) most of the export models using the longer and faster tapering upper vertical element are operating initially with much larger net values of capacitive reactance before they are lengthened to compensate and achieve the necessary conditions for electrical resonance. on the other hand, the larger diameter of the all tubing element in the sigma represents an increase in inductance when compared to the former, being one of the means by which the sigma doesn't require the extended additional length.

 

[Master Chief]

i'm saying that the Avanti Sigma 4 and the majority of export copies like the lw150, saliut 27 and others are electrically 3/4 wavelength in performance.

even the I10K is a 3/4 wave antenna, speaking electrically and not physically. see my previous post on the 5/8 wave configuration.

3/4 wave in performance? That would be BAD! I have pointed out in another thread that the loop at the bottom of the Avanti Sigma 5/8 brings the main radiator to 3/4 wave electrically, but performance wise, the loop is in the horizontal plane in order to not effect the 5/8 wave long radiator. As also pointed out many times in the past, any radiator over .64 length actually sees a drop in gain and performance due to signal distortion or scattering (for lack of a better word).

We agree that you need the 1/4 wave multiples for the antenna to work correctly, but the main radiating element on a Sigma 5/8 and the I-10K is no longer than 5/8 or .64 wave. If going longer than .64 wave ( .625 for 5/8 ) was better, everyone would have done it! They figured this little trick out 30 years before I was even born!

The Sigma IV is even shorter coming in at 1/2 wave effectively even though the physical length is 3/4 wave. The bottom 1/4 wave is not part of the main radiator.

 

[freecell]

the job of the loop is not as you describe. i suggest you read the patent over again.

and let me state it one more time. a 5/8 antenna may be that (+ or -) physically but electrically they are resonant 3/4 wavelength in operation. and why is that bad? because of the better than average match to 50 ohm feedline at all odd quarter wavelengths? or did you miss the part about the idea of the upswept radials in the first place being all about making the design much less sensitive to it's surroundings while increasing the gain and overcoming the loss in gain inherent in a straighteorward 3/4 wave design on the first place? these points are all addressed in the applicable patent.

 

[Master Chief]

Why is it bad? I suggest you look up one post and read it again. I even put it in BOLD to make it easier to find. As for the patent, I've read it.

 

[freecell]

then you completely missed the part about the purpose of the ring.

 

[Master Chief]

Nope, didn't miss it.

 

[freecell]

the electrical length of the diverging elements (radials) is one quarter wavelength which is about nine feet for antennas designed for use in the cb band. in order to broaden the bandwidth of the antenna in terms of maintaining a low standing wave ratio as a function of frequency, a conductive hoop or ring is affixed to the free ends (upper) of the elements via suitable mechanical connectors. the use of the ring not only broadens the bandwidth of the antenna but also effectively reduces the physical length of the elements to maintain their one quarter wave electrical length.
....................

# 4282531 page 4.

 

[Master Chief]

Hey, there it is again! Just like I remember it. What does it say that is contradictory to what I was saying?

 

[freecell]

the lengths of the elements without the ring would be 107 inches, whereas with the addition of the ring the lengths of the elements is about 89 and 1/2" inches. conductive ring diameter is 29 and 1/2 " inches.

that's what the ring does.

 

[freecell]

"loop at the bottom of the Avanti Sigma 5/8 brings the main radiator to 3/4 wave electrically........"

that's correct.
i thought we were talking about the sigma 4 and similar designs. let me rephrase....the loop in the sigma 4 has no such use.

 

[Master Chief]

OK, I see where you made the mistake. You are confusing the loop of the Sigma 5/8 with the loop of the Sigma IV.

I brought up the Sigma 5/8 when you mentioned the I-10K.

We're good! Let me know if you want me to delete these last few posts.