Here is something else I recently found out. If you saw the posted pic of my 11 meter modified Vector you will notice how much larger my loop is. I decided to try this large loop again on VHF to see where I might have gone wrong. Strange thing is I can make the loop a third bigger then stock with shorter then stock radials and get the virtually the same far field gain as the stock loop with longer radials. Do not mistake the obvious changes as having no effect because a careful balance of loop size to radial size must be maintained otherwise the gain drops. I just find it interesting that nearly the same gain can be seen with such different cone dimensions.
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Avanti Sigma4: An alternative view point
- Thread starter bob85
- Start date
Do you think I need to make a larger loop or just stay with the stock one?
What do you think / expect from the new Vector 3/4? Did you help to design that or did they take liberties by cutting corner$ to $ave?
shockwave, your latest findings with the larger hoop / shorter radials have me scratching my head,
i agree on the conditions making tuning up more difficult, its easier when we are in the trough of the cycle and signals are stable, even local signals are becomming more unstable with multipath like fluttering, peoples signals comming up stronger for a while then fluttering back down,
i am seeing sporadic changes in signal over distances as short as 5 miles more frequently.
i agree on the conditions making tuning up more difficult, its easier when we are in the trough of the cycle and signals are stable, even local signals are becomming more unstable with multipath like fluttering, peoples signals comming up stronger for a while then fluttering back down,
i am seeing sporadic changes in signal over distances as short as 5 miles more frequently.
Bob, I've scratched most of my hair off my head already working with this antenna. If I make the radials about 25% shorter and the loop about 25% larger the antenna shows nearly identical gain. Change only one of these lengths and the gain goes down noticeably. I know that does not make much sense considering how the height of the cone might effect the radiator. It does not look like the larger loop beats the longer radials however the difference is only a few thousandths of a volt on the digital signal meter and within the range of normal signal fluctuations at 50 miles.
I'm also considering the fact that I am doing this testing in receive on the FM broadcast band. Most of the signals I can tune against are circularly polarized (or so they claim). I'm seeing strong signal increases when I tilt the entire antenna towards a 45 degree angle facing the transmitter. My next round of tests will be against a closer LPFM station that is vertical polarized only. This is to eliminate the chance my adjustments to the cone may be slightly increasing the response of the antenna in the horizontal plane.
CDX, I think it's safe to use the stock loop size. While I've changed this quite a bit I have not been able to add more gain doing so. I can get about the same gain back by adjusting the radials with a bigger loop but I can't find more. With respect to the new Vector, I'm not sure if they considered the specifications of the antenna I have them make for me. For many years I've been ordering mine with 1/4 wave radials.
I don't think Sirio cut corners on the new Vector because some of the new parts are clearly more expensive to manufacture. For example the new ribbed metal radial and connector hub has 3 times the weight of the cheap old one. The ball that I don't like on top probably costs more then a straight whip. I've also noticed with the longer radials it appears you can take some length out of the radiator without seeing a drop in gain. Although my tests doing this never indicated more far field gain.
I just placed a new order for stock from Sirio and directed several questions to their engineers concerning the new Vector. Particularly what factors influenced them to make these changes. For example was computer modeling used to improve the design. Hopefully they will have the time to respond to my questions. I know the factory is busy now with a flood of orders after their summer vacation.
I'm also considering the fact that I am doing this testing in receive on the FM broadcast band. Most of the signals I can tune against are circularly polarized (or so they claim). I'm seeing strong signal increases when I tilt the entire antenna towards a 45 degree angle facing the transmitter. My next round of tests will be against a closer LPFM station that is vertical polarized only. This is to eliminate the chance my adjustments to the cone may be slightly increasing the response of the antenna in the horizontal plane.
CDX, I think it's safe to use the stock loop size. While I've changed this quite a bit I have not been able to add more gain doing so. I can get about the same gain back by adjusting the radials with a bigger loop but I can't find more. With respect to the new Vector, I'm not sure if they considered the specifications of the antenna I have them make for me. For many years I've been ordering mine with 1/4 wave radials.
I don't think Sirio cut corners on the new Vector because some of the new parts are clearly more expensive to manufacture. For example the new ribbed metal radial and connector hub has 3 times the weight of the cheap old one. The ball that I don't like on top probably costs more then a straight whip. I've also noticed with the longer radials it appears you can take some length out of the radiator without seeing a drop in gain. Although my tests doing this never indicated more far field gain.
I just placed a new order for stock from Sirio and directed several questions to their engineers concerning the new Vector. Particularly what factors influenced them to make these changes. For example was computer modeling used to improve the design. Hopefully they will have the time to respond to my questions. I know the factory is busy now with a flood of orders after their summer vacation.
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Just a small bit of info here.
First, I get a better SWR curve with rain on the antenna. It's been raining off and on for two days and this is what I'm getting with a wet antenna and wet surroundings:
28.755 ------- 3.5:1
28.305 ------- 1.7:1
27.855 ------- 1.3:1
27.555 ------- 1.1:1
27.405 ------- <1.1:1
27.205 ------- 1.0:1
26.965 ------- 1.2:1
26.515 ------- 1.5:1
26.065 ------- 2.0:1
25.615 ------- 3.5:1
25.165 ------- 4.0:1
Compared to this when dry:
28.755 ---------- 5.2:1
28.305 ---------- 1.8:1
27.855 ---------- 1.2:1
27.555 ---------- <1.1:1
27.405 ---------- 1.1:1
27.205 ---------- 1.2:1
26.965 ---------- 1.5:1
26.515 ---------- 2.5:1
26.065 ---------- 4.0:1
25.615 ---------- 5.2:1
25.165 ---------- 6.0:1
Second, and here's the part that I dislike, I placed a coax choke directly beneath the feedpoint of the antenna before the weather changed while everything was dry as before and the SWR on 27.205 went through the roof (try 10.0:1 for size. Needless to say, I did not key up for SWR anywhere else!). If not for the highlighted part of Marconi's quoted post I would begin to doubt the purity of this antenna's design. Every photo or drawing of these type antennas I've seen do not show the antenna isolated from the mounting mast, and whereas I did just that, I find that my antenna is obviously producing CMC in quantum quantities, utilizing the mast, or the coax, or both as part of the antenna.
Likely I am just the builder of a not yet perfected antenna and that is my problem. On the other hand, in all the efforts at modeling this thing with software did anyone provide for the mast being a counterpoise?
When the weather breaks and I have time I guess I'll try again to get a match on this thing with a choke in line. Were I a drinker, I'd likely get soused before fooling with matching this thing again. Guess I'll just have to grumble and grouse my way through it . . .
007,
id say just over 90" or however long the stock radials are when set as long as possible, im not saying that is optimum, its just what i was using right before i swapped it for the i-10k and lost the ability to talk to distant stations that i talked to regular on the vector hybrid,
shockwave,
do you think that the circular polarity of the transmitter could be skewing your results on vhf?
homer.
you must have a problem somewhere, isolating and choking a vector does not normally screw vswr up like you describe, the vector in my sig is mounted on 5ft+ of fiberglass tube and choked at the feedpoint, about 4-3/4 turns of 1/2" coax on 4.5" form.
id say just over 90" or however long the stock radials are when set as long as possible, im not saying that is optimum, its just what i was using right before i swapped it for the i-10k and lost the ability to talk to distant stations that i talked to regular on the vector hybrid,
shockwave,
do you think that the circular polarity of the transmitter could be skewing your results on vhf?
homer.
you must have a problem somewhere, isolating and choking a vector does not normally screw vswr up like you describe, the vector in my sig is mounted on 5ft+ of fiberglass tube and choked at the feedpoint, about 4-3/4 turns of 1/2" coax on 4.5" form.
Once again, Bob, thanks for a straight forward answer to my query.
Your reply sent me back to thoroughly checking everything. As it turns out, apparently the jumper from which I had made my choke was one I had not checked as I thought I had.. What I did was remove all the coax back to my antenna switch and put in a new single run with a choke wound from the end of this same coax. I put it in line and checked SWR again. Good this time, in fact, better than before.
I am almost reluctant to share the results, for I have read where SWR curve/bandwidth is controversial regarding whether an antenna is efficient or not. Some say too much bandwidth means poor efficiency. Others say "Bah, Humbug" to that. Personally, I don't know . . .
I'll go ahead and leap.
Here's what new coax with a choke under the antenna feedpoint has done for SWR:
28.755 ------- 1.5:1
28.305 ------- 1.4:1
27.855 ------- 1.2:1
27.555 ------- <1.1:1
27.405 ------- 1.0:1
27.205 ------- <1.1:1
26.965 ------- 1.2:1
26.515 ------- 1.8:1
26.065 ------- 2.2:1
25.615 ------- 2.6:1
25.165 ------- 2.8:1
The curve has gentled dramatically, with most improvement on the upper bands, as you can see.
What do you guys think? Can this be a reasonable bandwidth for this antenna? I would doubt this if I weren't reading the meter myself.
Next I hope to get it higher up, at least some, and I have another 5/8 wave that was the prototype (not as ruggedly built) for the one I had up for a while and used to make this antenna from. I want to get them both in the air at the same time just over a wavelength apart (yes I know, I know, but that's the best I can do for now) and switch between them for comparisons. I realize taking one down and quickly putting the other up in its place within a very few minutes is considered the best practice, but I figure what affects the one with regards to potential coupling will likely affect the other as well. As I said, it's the best I can do at this point in time.
Your reply sent me back to thoroughly checking everything. As it turns out, apparently the jumper from which I had made my choke was one I had not checked as I thought I had.. What I did was remove all the coax back to my antenna switch and put in a new single run with a choke wound from the end of this same coax. I put it in line and checked SWR again. Good this time, in fact, better than before.
I am almost reluctant to share the results, for I have read where SWR curve/bandwidth is controversial regarding whether an antenna is efficient or not. Some say too much bandwidth means poor efficiency. Others say "Bah, Humbug" to that. Personally, I don't know . . .
I'll go ahead and leap.
Here's what new coax with a choke under the antenna feedpoint has done for SWR:
28.755 ------- 1.5:1
28.305 ------- 1.4:1
27.855 ------- 1.2:1
27.555 ------- <1.1:1
27.405 ------- 1.0:1
27.205 ------- <1.1:1
26.965 ------- 1.2:1
26.515 ------- 1.8:1
26.065 ------- 2.2:1
25.615 ------- 2.6:1
25.165 ------- 2.8:1
The curve has gentled dramatically, with most improvement on the upper bands, as you can see.
What do you guys think? Can this be a reasonable bandwidth for this antenna? I would doubt this if I weren't reading the meter myself.
Next I hope to get it higher up, at least some, and I have another 5/8 wave that was the prototype (not as ruggedly built) for the one I had up for a while and used to make this antenna from. I want to get them both in the air at the same time just over a wavelength apart (yes I know, I know, but that's the best I can do for now) and switch between them for comparisons. I realize taking one down and quickly putting the other up in its place within a very few minutes is considered the best practice, but I figure what affects the one with regards to potential coupling will likely affect the other as well. As I said, it's the best I can do at this point in time.
Almost the same curve as my IMAX. I use it on 10m with great success. Looks like you can use yours the same way - if you have your ticket!
Plan to get the ticket this winter when the weather runs me indoors. I can hardly wait.
Homer, the Sigma has a very wide bandwidth and what you are seeing is normal. The bandwidth can be increased even more with different tuning methods if this is your goal. By tuning the radiator to favor one end of the band and the gamma to favor the other, you can extend bandwidth further at the slightest expense of gain.
Bob, I'm not sure if the circular polarization of the TX stations is causing a undesired variable with my tests. That's why I'm moving to use a vertical polarized signal. I use a yagi beam to detect direction and angle between horizontal and vertical that has the maximum signal. What I see is many CP stations are really ellipticaly polarized with peaks that occur between horizontal and vertical.
When the reference signal has more horizontal component I find the shorter radials and larger loop provide more far field gain. When the reference signal has more vertical component I find the longer radials and close to stock loop provide more far field gain. At first I couldn't figure out why one design would not work best with all of the received signals. Then I found this polarization variable.
I assumed by some manufacturers specifications that circular polarized antennas would be close to circular. Few stations in the NYC area are. Each one has peaks in different planes depending on the size of the face of the tower the bays are mounted on. I see problems with peaking the gain of a vertical antenna against a signal that does not have at least equal or all power in the same vertical plane.
I think it's reasonable to suspect that the shorter radials and larger loop may broaden the response to signals off of vertical polarization. This is not desirable if the goal is to provide maximum far field vertical signal gain. I'll be doing more testing against signals with confirmed peaks in the vertical plane to confirm this as soon as I can.
Bob, I'm not sure if the circular polarization of the TX stations is causing a undesired variable with my tests. That's why I'm moving to use a vertical polarized signal. I use a yagi beam to detect direction and angle between horizontal and vertical that has the maximum signal. What I see is many CP stations are really ellipticaly polarized with peaks that occur between horizontal and vertical.
When the reference signal has more horizontal component I find the shorter radials and larger loop provide more far field gain. When the reference signal has more vertical component I find the longer radials and close to stock loop provide more far field gain. At first I couldn't figure out why one design would not work best with all of the received signals. Then I found this polarization variable.
I assumed by some manufacturers specifications that circular polarized antennas would be close to circular. Few stations in the NYC area are. Each one has peaks in different planes depending on the size of the face of the tower the bays are mounted on. I see problems with peaking the gain of a vertical antenna against a signal that does not have at least equal or all power in the same vertical plane.
I think it's reasonable to suspect that the shorter radials and larger loop may broaden the response to signals off of vertical polarization. This is not desirable if the goal is to provide maximum far field vertical signal gain. I'll be doing more testing against signals with confirmed peaks in the vertical plane to confirm this as soon as I can.
Wait 'til you guys see my imax swr curve... I'm absolutely in awe. I've never seen an antenna so wide. I'll make sure to also post the other measurements such as the guy wire lengths and total mast height.
I'll have to measure it tomorrow since I have it down for testing the Saliut, but that test will have to wait another week or so.
It's (the Imax) something like 6 megs wide at 2:1 swr. I've never seen anything like it.
I'll have to measure it tomorrow since I have it down for testing the Saliut, but that test will have to wait another week or so.
It's (the Imax) something like 6 megs wide at 2:1 swr. I've never seen anything like it.
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homer,
i agree with shockwave, thats not an unusual bandwidth, i have seen them wider than that when measured at the radio end of a fairly long feedline,
i used my vector hybrid on 11mtrs and 10mtrs with good results on both bands and no tuner needed to keep the radio happy.
shockwave, if what you are seeing regarding the hoop and off vertical polarity can be confirmed, you added another dimension to the sigma enigma
i agree with shockwave, thats not an unusual bandwidth, i have seen them wider than that when measured at the radio end of a fairly long feedline,
i used my vector hybrid on 11mtrs and 10mtrs with good results on both bands and no tuner needed to keep the radio happy.
shockwave, if what you are seeing regarding the hoop and off vertical polarity can be confirmed, you added another dimension to the sigma enigma