Modified Vector 4000

[Shockwave]

Hello Marconi,

The gamma match is a variable capacitor that also forms a variable inductor. By sliding the gamma rod in or out of the gamma tube you are changing the capacitance. By sliding the gamma bracket up or down the driven element where it attaches to the gamma rod, you are changing the inductance.

One experiment I've conducted used a gamma match on a driven element and was able to tune the element for flat VSWR while adjusting the length of the driven element all the way from 1/2 wave to 5/4 wave. The gamma had much more tuning range then I originally expected and seemed to be able to tune almost any length radiator.

The one exception where the gamma could fail to give a match would be if the driven element were significantly shorter then what would be required for resonance. To add electrical length to the antenna we slide the gamma bracket more towards the grounded part of the driven element. At some point this stops looking like adding more radiator length to RF and starts to look like a short circuit.

Generally speaking when an antenna is too short to resonate, we add inductance to the matching network in order to cancel out capacitive reactance. When the antenna is too long, we add capacitance to cancel out inductive reactance. The gamma can do both however, it has limitations when the antenna is too short.

 

[Marconi]

Thanks for your remarks Shockwave. I re-read my post and I think I was confused in my argument and maybe got things backwards. I am trying to get back to posting, but I'm still recuperating from a recent 7 days in ICU flat on my back. I'm very weak and my thinking is not clear enough yet for detail discussions.

Right now I’m staying with my daughter until I get my strength back. I had a bout with Aluminum oxide inhalation poisoning that resulted in pneumonia. During the stress with my lungs being inflamed, my heart went A-Fib and my condition was all complicated with my diabetes as well.

A caution to everyone, be careful and work cleaning your aluminum antennas---in a well ventilated area only.

 

[CDX-007]

For those that were wondering what my measurements on this antenna are......Here you go. The vertical whip is 29 feet 7 and 1/4 inches long from the bottom of the connector bracket to the tip of the whip. The four radial arms are 81 and 1/2 inches long from end to end. The loop is 129 inches in circumference. The gamma is simply adjusted for lowest VSWR. Sorry I did not measure the gamma and I did use a home made Teflon gamma match with a weatherproof HN connector.

You may notice this last version of the antenna is more sturdy. I used the parts from two Vector 4000 antennas so that I could double up the lower sections and cut the flimsy top sections off. The four black plastic arms that hold the radials in place are also taken from two antennas. The ends were cut and then two pieces were screwed together with 4-40 hardware to make them longer.

The antenna was tuned on 11 meters and still provides under 2:1 VSWR on 10 meter SSB. The gain and bandwidth with the larger loop seems better to me and certainly exceeds what is possible with a 5/8 wave. The main advantage of the gamma match versus a coil with a tap is that a gamma allows you to tune out both capacitive reactance and inductive reactance. The coil only allows you to adjust the inductive component.

Giving this project a little thought, I believe I can use the ground hub of my other Penetrator base for holding the cone arms and make a Gamma match. What's the chance you could post the measurements of the Gamma?

Is the main radiator insulated from ground at the bottom or DC to ground & the radial arms?

 

[supergonzo]

OK, so how does it perform? And against what and how did you measure?

 

[Robalo]

i hope this helps, i have one of these antennas, i used to have the original sigma 4 and im pretty happy with them

 

[jazzsinger]

Thanks for your remarks Shockwave. I re-read my post and I think I was confused in my argument and maybe got things backwards. I am trying to get back to posting, but I'm still recuperating from a recent 7 days in ICU flat on my back. I'm very weak and my thinking is not clear enough yet for detail discussions.

Right now I’m staying with my daughter until I get my strength back. I had a bout with Aluminum oxide inhalation poisoning that resulted in pneumonia. During the stress with my lungs being inflamed, my heart went A-Fib and my condition was all complicated with my diabetes as well.

A caution to everyone, be careful and work cleaning your aluminum antennas---in a well ventilated area only.

Hope you have a speedy recovery Eddie,all the best mate.Take it easy.No antenna is worth dying for.

 

[supergonzo]

Not to spill drinks at someone else's party. BUT I have a Sirio 7/8 wave and a Hygain 5/8 penetrator both on my roof, both tuned, same coax lenght, same SWR..etc.etc.
The Sirio hears better than the Hygain, however the Hygain so far out talks it. The S/N ratio of the Sirio appears to be better than the Hygain, probably since its 10 feet taller. However the Hygain appears to put out better both locally and distant ground wave.

I have read the Avanti patent and I am interested in how the modified version stacked up to the original configuration, which I am using. I believe the 3/4 wave length version which would bring it in at about 27-28 feet with the regular 15 degree angle upswept radials may be the better performer than the 31 1/2 foot 7/8 wave version. I am going to change the length today to the 3/4 version and see if their is any appreciable difference.

This may shed some light on the subject

http://www.hamhelpdesk.com/antennas/58-wave-j-pole-vs-12-wave-j-pole-eznec-shootout.html

And this

http://techdoc.kvindesland.no/radio/vhf_antennas/20061030163006789.pdf

 

[bob85]

31.5ft is too long for the vector imho, somewhere between 29.5 and 30.5ft depending on radial angle and height above ground is about right,

the avanti uses a thicker radiator with only 3 radials so it needs to be shorter than the 4 radial vector for the same electrical length,

when both are tuned for best signal the longer vector 4000 outperforms the stock length avanti.

 

[supergonzo]

Ok, reduced antenna size to 29' 6" using standard radial setup, and now with a choke below the coax and the antenna is now attached to a thick fiberglass mast instead of steel mast. I had suspected some feedline radiation on the mast and coax, so took these steps to eliminate any stray RF. It seems to have helped.

Now transmit and recieve better on Sirio, the antenna is exactly the same height as the Hygain Penetrator, so far so good, I will evaluate the next few days.

From the man L.B.C himself

"The 5/8-wavelength pattern is usable, but at a lower level than a standard J-pole. The gain at a 6-degree elevation angle is about 2.5 dB lower than for a standard J-pole (2.6 dBi vs. 5.1 dBi).

The lesson that we might take from these models is that the standard-type J-pole's best radiator length is in the vicinity of 1/2 wavelength--as adjusted for the match section requirements and the element diameter."

 

[bob85]

good to hear you got the vector working better supergonzo,
is the penetrator also isolated from the mast ?, are they at the same feedpoint height?
some time spent making adjustments can yield better signal performance and bandwidth,

i spoke to CEBIK several times via email about the sigma/vector antennas.

 

[supergonzo]

Yes is the answer to both questions.
Ok, so what did he say?

 

[W5LZ]

I won't make bets on -what- the 'Ceeb' said, but I will bet that it wasn't what would be commonly thought.
- 'Doc

 

[bob85]

from one of my earlier posts heres the basics of what cebik said when i asked him about the sigma style antenna,

lb cebik ( rip ) told me there was more going on with that design than is immediately apparent to most people,
i fully explained what i was doing and what the results were,
he said that in the real world of earth masts and feedlines as opposed to freespace models, the radial angle makes little practical difference to the angle of radiation, that is untill we fold the radials up towards the radiator,
then a none aparent colinear array is possiblle that will outperform any conventional groundplane,
he said my test results were very much possible but was reluctant to get involved with the pages of meaningless arguments that such misunderstood antennas can generate,

look at transmissionline mode and antenna mode currents in a j-pole,
look at transmissionline mode and antenna mode currents in a gamma fed antenna,
look at transmissionline mode and antenna mode currents in an open sleeve antenna with different sleeve to monopole length ratios,

i cannot say with 100% confidence how the sigma operates but the common j-pole is not the answer,

 

[bob85]

heres a post i made on cbjunk when MC jumped ship explaining how i came down this road of thinking.

Re: avanti sigma4 an alternative view

by bob85 » Wed Feb 18, 2009 4:53 am
thanks for the comments guys, the sigma4 is not an antenna you can look up in a book like other commonly used antennas, consequently as cebik said it is very much misunderstood,

you may wonder how i came to my conclusions,
well it all started when i first posted about the sigma on wwrf, discussion/arguments ensued,
MC put forward a compelling argument backed by what an avanti engineer told him, it all sounded very plausible apart from one problem,
i had built jpoles for 27mhz and the sigma did not perform like a jpole at all for me, i had a gut feeling that there must be another explanation some addition from the basket that overcame the traditional problems of pattern breakup with radiators longer than .64wave but the only facts i had was the fact i knew what i and others had observed,
comming to terms with that been an illusion was not on the agenda just yet, not until i had done some research,
since then me and mc have taken almost every opportunity to have a poke at each other whenever the sigma4 gets a mention

,

we had something that a few people were intersted in but we did not agree on how it worked or how well it worked in practice,
i knew what i had been seeing for years but i wanted to know why some folk did not, i was pretty sure avanti had not invented something that nobody else had ever seen before, it must work on known principles,
i looked at the other things lou and herb had designed for clues and found none, lou was a kind of inventor, his field of invention was not restricted to antennas,

after the usual trawling the net / antenna books and finding nothing that seemed applicable other than an idea that if it did outperform other antennas it could not be any single element antenna i could find so in my mind the whole antenna must radiate just like it said on the box,
as unusual as it may seem for cb antennas i actually believed what it claimed and what the patent claimed but had no real idea how that could be, what they claimed fit what i observed but why?,
the patent seemed long winded for a tall story and it was herbs name on the patent not ampowers,
the sigma was not the only antenna avanti made that had people baffled, the astroplane does the same thing but more on that one later,
avanti thought out of the box, not following convention,

back then only one person agreed with me that i knew of, he claimed the lower portion radiated but getting anything else from jack ( freecell ) is hard work or should i say he likes to make you work for your information,
he did say one thing, that i should not give up and throw years of experience in the bin,

after corresponding with cebik and him not falling out of his chair laughing but on the contrary said it was possible and you can make a none apparent colinear array i wanted to know more,
i could not find anything about none apparent colinears,
what did he mean "its not apparent to most people" and usually generates lots of arguments,
hell yeah, he was right about the arguments that bit was easy to understand, what about the rest,

i started searching different ideas like "radials radiate in phase with vertical radiator" etc and eventually came across the open sleeve antenna or skeleton sleeve fed monopole,

holycow batman, this antenna has all the ingredients im looking for,

it can be 3/4wave or slightly longer,
it has radials folded up beside the radiator like cebik said,
the radials radiate in phase with the upper portion of the radiator in a colinear effect improving gain like cebic said,
it could operate in two modes ( antenna mode and transmissionline mode ) i figured if id never heared of two mode antennas then it was probably not apparent to most other people like cebik said,
some referances to the skeleton sleeve antenna call it a form of jpole like mc's avanti engineer said,
a form of jpole with a twist as mc said it may be ( after some poking ) lol,

i punted the idea around a few people with no negative comebacks and one positve then pondered on it while still looking for alternatives, so far i have found none that seem to fit as closely as a modified form of open sleeve antenna,
it ticks all the boxes imho,

cebik told me that the sigma would not be easy to model and get accurate results, i tried and got kind of lost in eznec4,
sadly by the time i had gained enough confidence in the idea to contact cebik and ask him "am i right in thinking the sigma style antennas operate on the principles of open sleeve antennas" hed gone silent key

,

thanks to all who have been involved in the sigma debate over the last 5 years or so

both on the forums and in pm/email,
i suggest you do your own tests and decide for yourself the validity of my conclusion, let us hope we have it figured out within the next 5 years

 

[DIRTYWHITEBOY]

Ordered me an LW-150 today,gonna see what all the fuss is about:w00t: