Modified Vector 4000

[mackmobile43]

I tuned the .64 for bandwidth and swr with the vertical section and gamma respectively, I should have fooled with the tapping point of the gamma but there again my lazy (C) got the best of me once more as I would have had to redesign the tapping point clamping bracket to the vertical section, whether or not this would have helped we'll never know as far as I'm involved.

If Bob or some one else comes up with something viable to optimize this antennas view of the horizon or give it more gain without driving it north or south in bandwidth I would gladly lay it down on the ground for that.

I do get very good signal reports in dx but I'm sure it's got a lot to do with the excellent conditions mutha nateur is supplying.

 

[Marconi]

I tuned the .64 for bandwidth and swr with the vertical section and gamma respectively, I should have fooled with the tapping point of the gamma but there again my lazy (C) got the best of me once more as I would have had to redesign the tapping point clamping bracket to the vertical section, whether or not this would have helped we'll never know as far as I'm involved.

If Bob or some one else comes up with something viable to optimize this antennas view of the horizon or give it more gain without driving it north or south in bandwidth I would gladly lay it down on the ground for that.

I do get very good signal reports in dx but I'm sure it's got a lot to do with the excellent conditions mutha nateur is supplying.

Mack, your tuning idea makes sense, but I use an analyzer, and for better or worse, I think it is the only way to tune. Even my Autek VA1 is affected by the feed line when I have standing wave on the line. I try to tune at the feed point when I can, and would use a tuned 1/2 wave line when I can't. Using an SWR meter usually always insures you will see feed line transformation that affects any meter's results in a negative way---if your system is not purely resistive at resonance, R=50, X=0 or really close.

I go to a lot of trouble to tune---scanning in 100 khz steps to produce a bandwidth curve like I show in my album on Antenna Work Sheets. It is sort of like Bob does with his MiniVA, but his does it automatically in seconds and mine takes a lot of work. My meter is not as accurate either, but I think I can get close with it. When I get close I start tuning in 1/16" - 1/8" moves at times and I can still see tuning differences. I use to make 1/4" adjustments at a time, and I always thought I was passing the sweet spot right-on-by and missing it.

I can't prove to you that any of this makes a world of difference, but I believe it can make a big difference if I can see a bandwidth curve develop a dip.

With a gamma this procedure might not work the same, but I still think small steps after you get real close is the way to go. The tuner on the I-10K seems very receptive to this process, and so did the A99 when I tuned it to 27.205.

What you are doing is fine if you want to work your radio, but if you want to do a super tune like Bob does, then you have to be more careful and test your results with each adjustment. Now Bob indicates Shockwave has a simpler process where I think he builds a special receiving loop antenna and uses a field strength meter, but I'm not sure.

IMO using DX contacts is not a reliable test of gain. In fact using local signals can also raise issues that have to be considered.

 

[Shockwave]

I believe my loop is too big on my Vector. When you read the original Avanti patent for the Sigma IV it suggests that increased gain can be had with a larger distance between the radial ends and the main radiator with a larger hoop. Extensive field testing an experimenting with the antenna in EZNEC+ are confirming the exact opposite!

Most of my work has been done perfecting an FM broadcast version of this antenna. It just so happens that it's radials are just over 1/4 wavelength with a 1/4 wave loop. Those radials are longer then the original Sigma and early Vector. I've been told the new Vector has radials that are longer then 1/4 wave. Bob85 has confirmed an increase in gain with the longer radials and is what I see at 98 MHz too.

I think we will find the new Vector has the right cone section and may be similar to Bob's 11 meter design. I question shortening the radiator from 7/8 wave to 3/4 wave on the new Vector because in field tests on 98 MHz .82 wave always shows the max gain. EZNEC+ however, does show the shorter radiator to give more gain. It also shows that the tighter the radials are to the main radiator, the higher the gain. This can present design problems at high power because the radials can arc over to the radiator if they are too close.

Henry has been kind enough to send me a model he made of the Vector in EZNEC+. I am new with working in this program and find building the model difficult. I am able to easily change any of the dimensions in the model to experiment. If anyone else out here works with EZNEC I would like to share this model with them in an effort to confirm the model is the most accurate representation of the basic Vector design.

 

[mackmobile43]

Mack, your tuning idea makes sense, but I use an analyzer, and for better or worse, I think it is the only way to tune. Even my Autek VA1 is affected by the feed line when I have standing wave on the line. I try to tune at the feed point when I can, and would use a tuned 1/2 wave line when I can't. Using an SWR meter usually always insures you will see feed line transformation that affects any meter's results in a negative way---if your system is not purely resistive at resonance, R=50, X=0 or really close.

I go to a lot of trouble to tune---scanning in 100 khz steps to produce a bandwidth curve like I show in my album on Antenna Work Sheets. It is sort of like Bob does with his MiniVA, but his does it automatically in seconds and mine takes a lot of work. My meter is not as accurate either, but I think I can get close with it. When I get close I start tuning in 1/16" - 1/8" moves at times and I can still see tuning differences. I use to make 1/4" adjustments at a time, and I always thought I was passing the sweet spot right-on-by and missing it.

I can't prove to you that any of this makes a world of difference, but I believe it can make a big difference if I can see a bandwidth curve develop a dip.

With a gamma this procedure might not work the same, but I still think small steps after you get real close is the way to go. The tuner on the I-10K seems very receptive to this process, and so did the A99 when I tuned it to 27.205.

What you are doing is fine if you want to work your radio, but if you want to do a super tune like Bob does, then you have to be more careful and test your results with each adjustment. Now Bob indicates Shockwave has a simpler process where I think he builds a special receiving loop antenna and uses a field strength meter, but I'm not sure.

IMO using DX contacts is not a reliable test of gain. In fact using local signals can also raise issues that have to be considered.

The vfo and a good swr meter shows an swr curve pretty well also reflected wattage goes hand in hand with swr but it's only way I have to tune my antennas and as of yet I've not lost any electrical components due to a serious mismatch.


It nice to see and understand how an individual aerial reacts to different measurements but I'll leave that to the guys who have the equipment to prove or disprove those theorys.

 

[bob85]

fellas,
the new sirio uses the longer radials with the same hoop, the new radials are 106.5" rather than 90" making the electrical length of the radials significantly longer than 1/4wave, at least that would be the case if the elements were not placed in close proximity to the central monopole,

does the close proximity reduce electrical length and raise resonant frequency enough that the longer radials are actually near 1/4wave electrical?,
could this indicate that the important dimention is the radial sleeve length and not the radials electrical length,

sirio don't claim improved gain from the longer radials they claim the same gain with a lowered radiation angle,
when i was tuning up my own antennas i posted that i felt that i was somehow manipulating the radiation angle because the improvement in signals at 60+ miles fm was more than the claimed db or so of extra gain over a 5/8wave could have provided,
i still think this is more than likely what we are doing when tuning for max signals at distance rather than effecting significant changes in absolute gain,

the way i read the patent they are saying that wider radial angles using full length 1/4waves give improved gain, obviously if you set 1/4wave radials at 30 degrees the hoop would be 9 feet in diameter and not at all practical,
avanti claim a wider bandwidth by adding the hoop and reducing radial length but they don't say what that does to gain,
note that the sirio uses 4x 90" radials where the avanti uses 3x 90" radials making them longer including the hoop

i was warned by LB.CEBIK that getting accurate results when modeling the sigma style antenna with nec ect would be very difficult.

 

[Shockwave]

Having worked with the Sigma design in the FM broadcast field for many years, I've had several engineers familiar with NEC claim the antenna modeled in the program performed terribly. With a maximum gain occurring at 45 degrees above the horizon. Knowing the information NEC was producing was totally inaccurate, I had little interest in the program.

Henry HPSD has completely changed my mind about EZNEC+. Apparently the new versions of the program are much better at modeling the antenna. Henry HPSD has modeled the Sigma in the program and gave me the file he made. The results looked so impressive I immediately purchased the new version of the program and scaled his model to fit my FM broadcast version. The sidelobe gain was within 0.1db of what was actually measured in the field!

The program also produced a wealth of other important information like a radiation angle of 8 degrees with a beamwidth of 22.9 degrees. Not to mention a beautifully detailed radiation pattern. No 5/8 wave is ever going to produce these results. Typically they have a radiation angle of about 16 degrees.

I also think the longer radials in close proximity to the radiator make them look shorter then they are. However, the longer radials still seem to drop the resonant frequency to some degree. This is easily compensated by adjusting the gamma tap point or radiator length. This could be one reason the new Vector is shorter then 31 feet.

While Sirio doesn't claim more gain, I was taught that the only way to increase gain in an omni directional system is to lower the angle of radiation. By lowering the angle of radiation, you simultaneously compress the beamwidth and produce more usable gain on the horizon. Am I not understanding this correctly?

While the hoop would be 9 feet on CB if you flared the radials out at 30 degrees, it's interesting to note the antenna does not need a hoop to perform. With the hoop removed and the radials lengthened to compensate, the antenna has nearly the same gain with reduced bandwidth. The most notable change was that the gain was not uniform in all 360 degrees. It produced peaks in the directions where the radials were, and nulls where the radials were not.

 

[Shockwave]

Bob, do you know what the main radiator length is on the new Vector? From the connector bracket to the radiator tip?

 

[bob85]

shockwave,
i don't know the exact length of the new vector as it comes from sirio, maybe mack or 212 measured theirs before they started tuning?

if the new eznec can produce accurate models of sigma style antennas thats great news, i can't say one way or the other as i don't understand nec and its limitations, i only know what cebik told me about trying to model that style antenna,

8 degrees sounds like what i would expect and i agree beyond what any 5/8wave can achieve,
i believe from tests that the sigma does not need to be mounted high in order to have a low radiation angle,

i would agree that colinears increase gain by compressing the pattern into a narrower vertical beamwidth, stagger phasing can beamtilt the pattern above or below the horizon at the expense of some absolute gain,
with single element antennas a higher gain does not always mean that gain is directed towards the horizon,
according to nec plots 5/8waves mounted at moderate heights have multiple narrow lobes and the dominant lobe is high angle,
while i have compared 5/8wave groundplanes to sigmas at 2 wavelengths to feedpoint in an open field where a 5/8wave should have a dominant lower lobe and still saw the sigma outperform the 5/8 groundplane,
most people don't have their antenna on a 73ft mast in an open field and i don't believe get the 5/8waves major lobe down towards the horizon in many cases, maybe if you live in a desert/ very poor soil and use 90 degree radials, but thats something cebik said needed looking at in more detail,

i would be interested to see what the new nec says happens when radial and monopole length ratios are altered, does it report manipulation of the takeoff angle as i suspected was happening or was some unknown ( to me ) effect leading me to think i must be manipulating the radiation angle?,
i saw little change in local signals but notable improvement in distant signals,

the pattern asymetry is interesting and what you see in an open sleeve monopole, avanti say you can use a solid cone, imagine the windload on that lol,

i have more questions than answers but no doubt of what that style antenna is capable of,
all i and friends that are buildng this style antenna at the moment can do is experiment with relative length ratios,
i decided on 6ft lengths of .063" wall 6061-t6 drawn tube for my upper radials with 4 avanti .058" wall 6061-t6 lower radials so i can experiment with longer radials and still have the high wind survival i need,


i am very happy that you and henry HPSD are taking the time to see what eznec+ reports,
the sigma style antenna is not nearly as simple as it looks but it is WELL worth the effort to try to understand how they are best optimised,

keep up the good work guys, we may get to the bottom of this eventually and put the modified sigma where it belongs,
if observed signals can be backed up by accurate plots it leaves little to argue about other than what is the best/most economical way to build a sturdy vector with high power handling

 

[mackmobile43]

Bob, do you know what the main radiator length is on the new Vector? From the connector bracket to the radiator tip?

http://www.cbtricks.com/ant_manuals/cte/sigma4_copy.pdf

 

[Marconi]

Mack, you failed to give us all the pages I think, the L3 part is missing.
The parts list shows the radiator is 5 telescoping sections only and gives no dimensions.
Regardless, I don't think it's possible to use this manual to figure what the real dimensions are, not enough information.

Do you recall how you figured out how long to make it or is the radiator length fixed, like my original Sigma IV?

 

[Henry HPSD]

Hello All !

Saw the thread today so thougth i drop in )

What i think so far...and perhaps already mentioned by some its a long thread already..
One could call it a co-linear since there are two current points on the antenna.

Futhermore the radials are there for the biggest part to profide a normal ohm value one wich we could adjust with a gamma-match.
If we would forget the radials and ring the impedance would be very Capacitive -J.
The Gain however more or less remains (+/- 0,5dB). (high angle)

The best thing wich comes along with attaching radials is a lower radiation angle.
The 3/4 wave in this case has got a nice low lob and a second lob a bit higher.
Actually it would be great for real dx through F2 and do a good job in with the sproadic E season aswell.
No big mistery..in general radials lower angle and do that for every 1/4 wave (5/8,3/4 etc)

Now...the biggest worrie i have so far is the gain that one can reach (+/-4,2 dBI ) is with a very thin radiator...that migth be the explination why the antennas are always brougth on the market a bit too thin to everyones believe.... ( not a fact!)
each time i enlarge the main radiater gain drops rappidly towards 2 dBi

Intresting antenna so far !

Kindest regards,

Henry

 

[Shockwave]

Hello All !

Saw the thread today so thougth i drop in )

What i think so far...and perhaps already mentioned by some its a long thread already..
One could call it a co-linear since there are two current points on the antenna.

Futhermore the radials are there for the biggest part to profide a normal ohm value one wich we could adjust with a gamma-match.
If we would forget the radials and ring the impedance would be very Capacitive -J.
The Gain however more or less remains (+/- 0,5dB). (high angle)

The best thing wich comes along with attaching radials is a lower radiation angle.
The 3/4 wave in this case has got a nice low lob and a second lob a bit higher.
Actually it would be great for real dx through F2 and do a good job in with the sproadic E season aswell.
No big mistery..in general radials lower angle and do that for every 1/4 wave (5/8,3/4 etc)

Now...the biggest worrie i have so far is the gain that one can reach (+/-4,2 dBI ) is with a very thin radiator...that migth be the explination why the antennas are always brougth on the market a bit too thin to everyones believe.... ( not a fact!)
each time i enlarge the main radiater gain drops rappidly towards 2 dBi

Intresting antenna so far !

Kindest regards,

Henry

Henry, I think the thin radiator effect would only matter in the lower part of the antenna since it forms a coaxial cone. I noticed that your wire lengths that form the loop are much smaller then the four 24 inch loop sections used on the Sigma design. I wonder if when you increase the diameter of the main radiator if you should also increase the lengths of wires 11, 12, 13, and 14 to around 24 inches. This may balance the effect out. I also think you will have to shorten wires 2, 3, 4, and 5 from 122 inches to 106.5 inches. I'm not sure if you tried this but it would help simulate the impedance we see with the thin wire radiator. When the inside conductors diameter increases, you have to increase the outside diameter to compensate. There may be more going on here then just that, but it's a start. I also agree the antenna definitely performs like a real collinear! The two separate currents generated by the coaxial cone base and the top radiator are clearly in phase with each other.

 

[bob85]

thanks for your input henry,
any work somebody does to try and understand the sigma style antenna is much apreciated by myself,

CEBIK called it a "none apparent colinear array" because he said it was not aparent to most people how they work, you seeing big changes in gain with changes in wire diameter could be the difficulty with trying to get accurate models with nec that he told me about,
i read that sleeve to monopole tube diameter ratios effect that style antennas performance, shockwave is on the right track imho

 

[Henry HPSD]

Hi All,

I am searching for "exact" measures of the antenne.
I can find the sizes of the antenna back in "82... but i would like a more "modern" version.

From the Sirio homepage i have so far:
Radials bottum 13mm thick 1,4 meter long going over in 10mm thick 1,31 meter
So the total radial length would be 2,71 meter.

The Radiator length total is 8.48 meters.
The diameter starts at 37mm and is 1,4 meters long.
second tube is a 33mm 1,4 meter long

Everything else is a guess to me.

With guessing....
third tube 29 mm 1,4 meter long
fourth tube 25mm 1,4 meter long
fitfth tube 21mm 1,4 meter long
sixth tube 17 mm 1,4 meter long
seven tube 13mm 1,4 meter long.

Could someone give me better sizes?

(inches feet also fine!)

The biggest question for me now is :the top distance of the radials to radiator.(where the round circle is).

Kind regards,

Henry

 

[bob85]

henry,
the hoop diameter is 30" in all versions,
i only have the old longer monopole versions of the vector to take exposed tube measurements from.