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Homer's Qv4k

Yes, I can easily adjust length of the vertical. If you notice the second set of SWR readings were with the antenna at its shortest of the three lengths, and the SWR was not good for what I wanted. Whereas I show only one Gamma set on easch of the posted results, I did several Gamma adjustments on each one with varying results. I posted the best of each only.

I can shorten anything I need to, or lengthen if needed, but this antenna is designed for optimum performance within certain parameters, and I am concerned with too many changes affecting the gain/toa to the horizon, etc.

Naturally, I am willing to do anything that can be undone.
 
id pm shockwave , he makes a version of this antenna for other frequencies and would be the best source of info (that i can think of) on modding them for that purpose .
 
I took the antenna down for tonight until the current storm system passes over. We are in the path of potentially very severe storms.

I'll have it up again quickly, but I'm considering some shorter thicker radials, and shortening the vertical in an attempt to get the SWR curve centered higher up, or at least smoother in its arc so it can embrace 10 and 11 meters fairly well. We'll see.
 
i hope those changes give what you're looking for (y)

did you get a chance to pm with shockwave yet ? if so what did he say ? what do you expect the thicker basket elements to do for you ?
 
Homer, from your VSWR charts it seems likely your cone is resonant too low in frequency. The two dips in the VSWR at different frequencies is characteristic of having the vertical radiator tuned at one frequency and the cone tuned at another. Being that the new radial length for the Vector is 106.75 inches and it's designed to tune both 10 and 11 meters, it makes me question if there may be something else going on with your cone. Did you use the stock loop length? I think the loop may be too large. Are you certain each of the four radials are equally spaced on the loop? That one can make a big difference. I assumed your target frequency might be around 27.7 MHz. You should have found a match with good gain at 27.75 feet. If the cone measurements are correct and you can't get a match with the vertical radiator at 27.75 feet, shorten the radials to 104.75 and work that gamma again.
 
Thanks Shockwave.

The loop is 31" diameter, the radials are 106.75", however I will remeasure it all for confirmation that I did not get it wrong.
 
Thanks Shockwave.

The loop is 31" diameter, the radials are 106.75", however I will remeasure it all for confirmation that I did not get it wrong.

Homer aren't all of your tubing diameters in the bottom portion of you antenna considerably larger than the Sigma4/Vector that you are using to determine your element lengths? The bottom of this design may well be like tuning the strings of a guitar, where everything needs to be exactly precise or recalculated for the situation at hand...else you're not likely to see controllable and/or similar results.

IMO, such precise details may be ignored with a typical monopole antenna to some degree, because the differences may be negligible, but the elements in this very long tuning section are likely more critical to tune and resonance. I find the same to be true in the bottom element of my Starduster vs. some of the knockoff models and in the construction of the AstroPlane and the arc of the tuning element to the mast. I can actually see the differences in performance when compared side by side. I'm not sure that I could tell otherwise and free standing, however.
 
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I think Shockwave and Marconi are on to something in regards to your situation Homer....the only other thing i can think of that might possibly affect things is IIRC you wrapped the hoop (pvc or HDPE i think)in foil tape...this alone may not be the answer but maybe in combination with some of the other things mentioned might possibly be a contributing factor

just my .02
 
Okay, Marconi, I am a little off, perhaps, and this may be the problem.

According to this graphic -

4749d1306272810-avanti-sigma4-alternative-view-point-vector-new-4000-336x640-.jpg


I should be about 30" diameter, it seems, or 29.5"

As for the length of the radials, 106.5" should be right.
 
Okay, Marconi, I am a little off, perhaps, and this may be the problem.

I should be about 30" diameter, it seems, or 29.5"

As for the length of the radials, 106.5" should be right.

Homer, I posted the following to you on QS forum.

Ole' Grampa said:
Homer, I think you're close enough to consider moving it to the higher mount. You may have to re-tune due to the change in feed line however. If it is easier to tune where it is now, then maybe I'd hook up the other line before going to all that trouble.

The other day I told Booty Monster that my gamma lies 3" inches outside of a plane between the two radials, but I think that could be misunderstood. My gamma is positioned outside of a plane between the two radials like the images tried to show, but the gamma is actually the same distance from the center of the radiator as the radials at that point, just like your antenna shows. The distance on my S4, between the OD of these elements, is 5" inches measured at the dog bone. At the feed point end of the gamma the center of the FP is about 3/4" away from the OD of the radiator, and the radials are about 1 1/4" from the OD of the radiator to the center of the radials, so the angles here are a bit different, but not much. Again, I don't know how much difference this will make if your measurements are not precise at this point in the antenna, but it has to be considered.

I think you also have to consider the diameter to length ratio for your radials.

Does the total overall length matter, I don't really know, but we have to consider what Bob and SW tells us about that. I haven't tried to make anything longer on my antenna as yet, and if I understand Bob correctly, I may not see a similar difference at a distance, simply because my antenna only has three radials instead of 4. On the other hand when I told Bob I could see a noticeable difference between 3 and 4 radials on my Marconi, he suggested the difference I saw was likely due to changes in conditions, and not the number of radials. So, I still don't know for sure about this, but that could also mean what Bob saw was also due to conditions. Check the dimensions real close and if necessary try and get them a little closer. Then see if you can get a better handle on the tune, and then work if for a while and see if you can tell how it compares to whatever else you have up, your 5/8 wave or the AstroPlane.

Within reason, I generally don't consider tune to be the defining factor in antenna performance, as most do. But, Bob makes a good argument for the collinear affect with the Sigma/Vector design, so I think tuning, in this situation, does bear some consideration. As a result, I think from my own experience that this antenna is very sensitive to its construction, you may not be able to get by with even a little differences, here and there, and still expect it to work as intended for best performance at a distance.

I'll also mention that my modeling of the Sigma4 did not bear out that the longer version was better...as far as gain and angle were concerned. My models showed the opposite, in that a bit shorter overall length showed more improvement. I don't recall if I made the radials longer or not, but that could be the difference we here about, but Sirio did make their New Vector 4000 model shorter for some reason, didn't they.

Homer, have you considered that the small amount of insulator material you use in your gamma may not provide the capacitance range necessary to counteract the inductive reactance in this antenna? I would like to know what the inductance for your antenna is at or near resonance? I have a feeling that your feed point may be showing more inductive reactance than desired. If I'm right, base on my assumptions from prior experiences, you may note your antenna is a bit deficient in the receive function. If you see a noticable difference when you change your feed line length, then I would consider such a tell-tale sign that reactance is the problem.

I could be wrong, but only some good old fashion on-air testing and comparisons work could help show that.

Good luck and keep us posted,
 
Thanks, again, Marconi.
I will be working to set things as close to what you've described as I can.
All of this info is helpful. i want the best I can do when all is finished.
 
SWR:

28.755 -------------------------- 1.2:1
28.305 -------------------------- 1.0:1
27.855 -------------------------- 1.0:1
27.405 -------------------------- 1.15:1
27.205 -------------------------- 1.2:1
26.965 -------------------------- 1.25:1
26.515 -------------------------- 1.1:1
26.065 -------------------------- 1.35:1
25.725 -------------------------- 2.0:1
25.615 -------------------------- 2.3:1
25.165 -------------------------- 3+

More later. Chores first.
 
There are changes that were made to the Qv4k that has resulted in movement in the SWR that I find favorable. Primarily, the changes were made to the 4 radials - length and diameter of the elements - and to the gamma match. Also, the length was reset to 29' 1".

The above posted SWR was where I landed with those changes while the antenna was mounted on the temp testing pole very near the house and close to the ground, if I recall around 14' from the earth.

This is a view of the changed radials: 90" from where they bend away from the center vertical to the tip ends, and 3/4" diameter.

4868.jpg


Closer up while the antenna is laying on its side you can see the close-ups of the changes to the Gamma Matching setup. The dogbone is now set at 36" up from the feedpoint of the antenna, the gamma tube is now 17" x 3/4" OD, the rod is 36" x 3/8" and pulled out from the tube 25.5" which brings the tap point around 19". Additionally, between the rod and the tube there is a nearly snug fitting dielectric tubing running the entire inner length of the tube.

4884.jpg
4883.jpg


Here is a snapshot of the Qv4k sitting above the Yagi on the tip-over mast just as the sun is setting.

4887.jpg


After the antenna went up higher into the air, sitting just above the yagi about a foot, the SWR curve shifted upward some.

Here it is currently from the 2.0:1 reading upward:

26.515 -------------------------- 2.0:1
26.965 -------------------------- 1.2:1
27.205 -------------------------- 1.0:1
27.405 -------------------------- 1.0:1
27.855 -------------------------- 1.0:1
28.305 -------------------------- 1.2:1
28.755 -------------------------- 1.2:1

I do not know where the SWR goes upward from there as I ran out of frequencies on the DX88HL.
 

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