To 7/8 or NOT to 7/8, that is the equastion

[Needle Bender]

There certainly are differences in how they perform in our tests NB,
What causes it is open to speculation, i look at whats notably different and that's the full size radials and the matching,

good luck with your new vector, i see no harm in experimenting to see what works best for you,
some people swear by the gainmaster but in my yard on a 20ft pole it plays second fiddle to my 10k by a small margin..

Bob, you owe it to yourself to try that GM way up in the air, & far & away from all other RF 'irritants'.
-Mine squished the P500 by a full 2dB over 9 (1db over VS 3db over @ 16km) on my friend's Pro3 analog over multiple swaps & multiple days/ times of day.
- It was ~41' at the base and used 60'- 65' of LMR-400. I'm no longer at that QTH so it's all just a sweet memory now, and I didn't like the power limitation so I was talked out of it, but there just may be another 'modded' GM in my future. I just wish Sirio would do the mod at the factory. No doubt it would improve their sales.

And you know Bob, I'm beginning to wonder if the GM isn't so fickle that it performs differently based upon at which point in the current/voltage nodes within the coax it's seeing the RF at it's SO-239.
- AND if elevation above ground possibly radically changes it's pattern &/or characteristic TOA signature?
Things that make one go, "Hmmmmmn."

And 222DBFL, I plan to remove the top section & ball top hat and replace it with a Wilson 5000 whip installed into about 3/8"-1/2" solid stock for lower wind loading.
-I don't run more than a set of 3-500ZGs so I'm not concerned with any corona discharge.
Also, since it's a DC grounded radiator I doubt the missing top hat will result in any increase in static build-up.
We'll see.

 

[The DB]

And you know Bob, I'm beginning to wonder if the GM isn't so fickle that it performs differently based upon at which point in the current/voltage nodes within the coax it's seeing the RF at it's SO-239.

A note or two...

1) The "nodes" mentioned are only present when you don't have a perfect SWR match.
2) When such nodes are present their location is determined from the antenna's side, not the radio's. Because of this where they are in relation to the antenna does not change (unless the changed feedline is not long enough to get to them). It is the reflected signal (and its interaction with the forward signal) that generates these "nodes", and that signals source is the antenna'a feedpoint. Because of this, the antenna always sees the same feedpoint impedance, irregardless of how long the feedline is.

I don't like the term "nodes" here. A node, at least as far as antennas are concerned, are points of pure voltage or current (at least in theory). No such point exists on a feedline, not even close, unless you have a 100% reflected signal, which is an infinite SWR at the antenna's feedpoint.

- AND if elevation above ground possibly radically changes it's pattern &/or characteristic TOA signature?
Things that make one go, "Hmmmmmn."

Over time I have done modeling for various center fed vertical antenna lengths, from very short in relation to a 1/2 wavelength all the way to extended double zepp lengths, and at multiple different frequencies as well. In every case these antennas are affected by ground losses (and by extension gain) noticeably more when mounted closer to ground than ground plane (horizontal radials) antennas. It is almost like the ground plane radials have the effect of shielding the vertical element from the earth below. That being said, get the center fed antennas some height and the modeling software always shows the center fed models outperforming their groundplane counterparts when it comes to gain. When it comes to (near) center fed antennas, height is might appears to be even more apparent than ground plane designs.

When it comes to lobes in the pattern, this seems to be more a function of tip height and ground quality than antenna design. As an antenna is elevated more lobes form, and these new lobes have the effect of "pushing" the existing lobes further down. In general doubling the height of an antenna will cut the TOA of the lowest lobe effectively in half. The RF in the new lobes that form has to come from somewhere, and that somewhere is the existing lobes. This doesn't lessen the strength of the existing lobe, but instead makes it narrower. If you have antennas that have a significant difference in height, it is possible that the higher antenna has two or even three lobes (and their associated nulls) in the same vertical space that a single lobe takes up for the lower antenna.

All that being said, the models don't show any real difference between center fed and end fed designs at the same tip height when it comes to the TOA of the lowest lobe...


The DB

 

[bob85]

I don't doubt the gm is a great performing antenna, its the best white stick i ever tested here in the yard & i have seen it outperform imax 827 a99 on the same pole at several different locations,

If i wanted a white stick it would be a gainmaster id buy no doubt about that even though im not too impressed with their floppy build quality or their dislike of even 300w fm if you get long winded, sirio could have done much better for not a lot more money imho,

In this yard at the heights i can have my antenna the gainmaster is not the best choice for performance but it could be the best choice if bandwidth and less of an eyesore is important which its not at the moment.

 

[Needle Bender]

Similarly here Bob, but though I've ordered a Vector4K I'm still considering changing to Phillystran from guy wire and trying another GM, IF I can get the height I believe it needs, maybe 54' to the mount.
I happen to have several feet of Teflon mini-8 so a mod would be somewhat easy.
-If I KNEW it would perform as well as the V4K locally I'd just sell the V4K unopened due to the GM size, bandwidth & ease of installation.
But then I just know I'd be cutting coax and testing, testing, testing - 'til all the locals would want to run me out of town!

 

[Marconi]

OK, I'll enjoy hearing from anyone who has a thought, or several, about which to commit to with this 'Parts antenna'.

NB, I have some thoughts, and I'll repeat an incident I've told before.

Years ago I bought 3 CTE Saliut Larry 150 for some buddies. I had never seen this brand of antenna except in pictures. I had the antennas sent direct to the customers, so I never saw their antennas either. They were described to me as being about 30'> feet long as constructed, and that was a lot longer than my Sigma 4 at a little over 28' feet.

Two guys complained that their antennas had no "ears," but they talked OK as far as I and others could tell on the air. I was never able to resolve their complaints, even though I offered them full refunds of their money.

Some time latter another ham buddy told me a story about his Larry 150 and how he had to reduce the length to near 28' feet to get it to work right for him. He also claimed the CTE was designed to setup and tune for 10,11, and 12 meters. I could not be sure, but this idea may have something to do with the problem noted here.

This seems a bit self-defeating, adding an of out-of-phase 1/8 wave to the bottom of a nicely designed & correctly phased 1/2 wave radiator. Seems it would cancel the next 1/8 wave up, leaving only the top 3/8 to do the radiating.

I don't know if your explanation above results in such an idea as you note above, but when I add 2' feet + length to my New Vector 4K model, the model produces a very high maximum angle, the gain is poor, and the RF pattern above the top of the hoop shows a lot of wasted radiator.

So I'm left wondering why it would ever have gone into production if it's a poor performer compared to it's shorter older brother? And what about that monster BigMac 7/8? I've read it was the Big Daddy of them all.

I think it is fair to consider that the CTE kit was possibly designed to work on 10,11, and 12 meters and not specifically designed fixed at 11 meter like the Avanti and Antenna Specialists kits. Maybe this is why my guys reported such poor results.

I dunno, at this point I guess I'm leaning toward the Vector 3/4, partly due to the fact that Sirio offer it thus, and I'd expect they'd instead offer the 7/8 version if it were superior, and partly due to my concern for screwing up a really cool 1/2 wave design. The guys at Avanti weren't slug-heads.

Oh no, I'm writing a bloody book
-But if there's a chance the monster 7/8 would reign supreme...

I tend to agree that Sirio and Avanti were smart guys and might have had the right idea in their 3/4 wavelength designs, but that said I cannot explain Bob's results to the contrary using much longer radiators.

See my Free Space NV4K model below with 107" radials and a 31.6' foot radiator compared to a NV4K to specs.

 

[gamegetter]

NB:

I believe the GM and 4k are about at the same performance level. Just my opinion...
Which one will serve you best remains to be seen by your trial and error.

That having been said, set antenna at the highest elevation so that it can see the horizon in all directions. At that point nothing should be close enough to affect it.

Leave the rest up to mother nature and good luck in your quest.

 

[Needle Bender]

All awesome input! Thanx for that Marconi and great to hear from you! I hope all is going well for you.
Yes, makes sense, and you've convinced me to trust the "Big Two" - Avanti & Sirio, now, why the difference in length between THOSE two?
-Avanti was 27 7 and I believe Sirio V4K is only 26 8 or so. Can't be that much difference from 27.125 to 27.185 center 23/40 ch.

Then there's Bob85 and his/Shockwave's .82

But first, the stock Vector @ 45', just to set a bar of performance at this newer QTH, then,

...we'll see

 

[bob85]

NB,
The new vector has 1/4wave radials, the sigma has 90" radials,
the old vector had 90" radials and a radiator over 30ft long which was too long even in this yard.

 

[Marconi]

Yes, makes sense, and you've convinced me to trust the "Big Two" - Avanti & Sirio, now, why the difference in length between THOSE two?
-Avanti was 27 7 and I believe Sirio V4K is only 26 8 or so. Can't be that much difference from 27.125 to 27.185 center 23/40 ch.

Based on the dimensions that Bob reported for a New Vector sometime back, I agree with your dimensions noted above. The small differences you note might make a little difference in the tuning/frequency results for these two, but I doubt there is a measurable difference in the performance results we could see just using our radio's Smeter.

However, if there is such a difference to be noted...then it maybe due to the difference in the radial lengths, 107" vs 90.5" inches like Bob suggested.

If this is true, however, I would figure such a difference to be very small at best.

Then there's Bob85 and his/Shockwave's .82

If you are going to try and prove SW's .82% idea, then you have a lot on your plate. Did you make a typo above when you noted your setup at 45' feet as a bar for performance...you have been talking about 54' feet in earlier test ideas you posted.

I can only tell you in real world testing of my Sigma 4 that this antenna can be a bugger to tune. I also suspect that the tune might vary noticeable on changes in height. If your not lucky with the height you use...you may have to deal with common mode currents that are strong. If you isolate by raising the antenna a few inches it my help, but I think it necessary to also add a choke that works.

See this old thread,

http://www.worldwidedx.com/threads/vector-4000-wont-even-calibrate-to-set-swr.99520/

I think you might find some discussion on the Saliut's dimensions.

Personally I favor the Gain Master's center fed 5/8 wave over the NV4K, and for me the GM also shows no hint of CMC's and has a lot wider bandwidth...if that matters.

 

[Needle Bender]

Based on the dimensions that Bob reported for a New Vector sometime back, I agree with your dimensions noted above. The small differences you note might make a little difference in the tuning/frequency results for these two, but I doubt there is a measurable difference in the performance results we could see just using our radio's Smeter.

However, if there is such a difference to be noted...then it maybe due to the difference in the radial lengths, 107" vs 90.5" inches like Bob suggested.

If this is true, however, I would figure such a difference to be very small at best.



If you are going to try and prove SW's .82% idea, then you have a lot on your plate. Did you make a typo above when you noted your setup at 45' feet as a bar for performance...you have been talking about 54' feet in earlier test ideas you posted.

I can only tell you in real world testing of my Sigma 4 that this antenna can be a bugger to tune. I also suspect that the tune might vary noticeable on changes in height. If your not lucky with the height you use...you may have to deal with common mode currents that are strong. If you isolate by raising the antenna a few inches it my help, but I think it necessary to also add a choke that works.

See this old thread,

http://www.worldwidedx.com/threads/vector-4000-wont-even-calibrate-to-set-swr.99520/

I think you might find some discussion on the Saliut's dimensions.

Personally I favor the Gain Master's center fed 5/8 wave over the NV4K, and for me the GM also shows no hint of CMC's and has a lot wider bandwidth...if that matters.

I can't test the NV4K higher than 45' above the roof due to the more massive mast loading. It's basically an unguyed mast until it's all thw way up when the guys tighten.

And yes, another GM isn't out of the question, I just wanted to 'Play' with an NV4K and test Donald's (& other's) claim of it's superiority to the Penetrator.
I have decided to make the bottom right at 36' where the P500 is currently & temporarily until the new rolls of non-metallic guy line show up, after which they'll both go to 45' for another head-to-head.

I'll notate multiple TX & RX signal strengths/distances for about a week or so with each.

I'll need a small crew here to handle the loose guy lines if/when the NV4K goes up to 54'! That would be awesome, 81' at the top equals right at 2 wavelengths at the high current node.

Also, I did a few calcs and it appears 90.5" plus 1/8 the ring circumference, plus the material circumferences equals right at 1/4 wavelength on the shorter cone, where the NV4K cone covers a full 1/4 wavelength of inverted current.

 

[Marconi]

Yes, makes sense, and you've convinced me to trust the "Big Two" - Avanti & Sirio, now, why the difference in length between THOSE two?
-Avanti was 27 7 and I believe Sirio V4K is only 26 8 or so. Can't be that much difference from 27.125 to 27.185 center 23/40 ch.

You ask "Why" the Vector is a bit shorter. In part there may be a difference in length due to the Vector's small top hat. There maybe some difference in tubing diameters, but my models don't take the tapper into account due to an Eznec limitation using tapper.

 

[Needle Bender]

You ask "Why" the Vector is a bit shorter. In part there may be a difference in length due to the Vector's small top hat. There maybe some difference in tubing diameters, but my models don't take the tapper into account due to an Eznec limitation using tapper.

Well, I have to expect, (especially with all the cool engineering being done there), Sirio to have done their homework with regard the cone & radiator lengths, although Avanti as it's original creator were no slouch in terms of creative designs, I suppose with time come upgraded technologies providing perhaps a better means of securing more accurate test results, hence the discrepancies in lengths of the cone, Gamma & radiator in comparison to the original Avanti Sigma4.

My NV4K arrived earlier and after investigating it's construction I'm less than impressed with the upper radiator tuning design, seems far less than overbuilt - to be kind.

Still, it appears to be functional so up it goes, after a few small mods to add slits in line with where the screw holes are & hose (jubilee) clamps at the top of each of the radiator tubing swages.

-I thought screw-together radiators died with the '80s

Causes at least 1/2 the potential connection area to be pulled to one
side leaving a slot where water ingress is welcome and oxidation finds a home inside the tubing via simple condensation even if well taped & sealed on the outside of the radiator.

-I prefer to have a near 360° contact area at each section of radiator, without screws to back out over years (months?) of wind vibration.

I've also considered removing the top 3" of the 5/8" section which has been shrunk by swaging to accept the 3/8" section, allowing an additional 3' of 1/2" tubing to be added, into which the top 3/8" tube would finish off the top of the full-length radiator with the hole for the 1/8" tuning rod relieved to accept the larger diameter lower crimped 1" of the top hat, thus completely eliminating the diminutive 1/8" rod but retaining the attractive spherical top hat.

I'll simply slide the 3/8" up/down inside the 1/2" tube for tuning/ balancing radiator length against Gamma adjustment.

Since I've recently relocated my QTH, no doubt I'll be hunting down my necessary tools (scattered about in THREE storage units) for such a project for better than a month.
-I may just put it up as-is out of the box for now, just to get a feel for it's performance.

Nice feeling to open a brand new NV4K antenna box

 

[bob85]

Be careful NB,
i have tried different permutations of beefing vectors up,
adding any extra weight or wind load to the upper radiator makes them even more floppy,
i ended up honing the hub to take an AVANTI radiator,

Slotting to get rid of the screws is a good idea, The screws rot and the holes enlarge with the constant rocking in the wind,

i would use lightweight breeze Aero Seal hose clamps like the i-10k uses & trim any excess band with a dremel,
They are- strong enough and lighter than pressed hose clamps.

 

[222DBFL]

Man NB, posts your results or some readings on an analyzer if you have one please. I would like to see what it does at like 20-25ft to the feedpoint. I can get an idea at least of what to expect. And pics of the upgrades that you do make. It would me much appreciated. I'm at the cross road of just getting another sirio tornado, or to try the vector 4000. I too like the slits and hose clamps which will be done to next antenna as well. Go light weight as possible!!

 

[gamegetter]

NB:

When you say test at 45', do you mean antenna tip height at 45' or is that where the base(feed point of antenna) will be located?

Sorry if I missed this before.