Avanti Sigma4: An alternative view point

[freecell]

i wrote:

"moving the radials upward in close proximity to to radiating element compresses the electric and magnetic charge while increasing the capacitance between the radials and the vertical element. this creates additional loss resistance. it drives down input resistance (now you need the gamma match) while also driving the frequency down the band, now requiring the lengthening of the vertical element by +or- 5.5" to bring it back up into the band and with the additional loss the swr bandwidth is wider than it should be. it is not well known that as loss resistance increases in an antenna system that the bandwidth will be widened but for all the wrong reasons. claims of ever increasing swr bandwidths mean more Rloss / loss resistance (bad) and less Rrad / radiation resistance. (bad) altogether it all adds up to reduced antenna radiation efficiency."

correction:

moving the radials upward in close proximity to to radiating element compresses the electric and magnetic charge while increasing the capacitance between the radials and the vertical element. this creates additional loss resistance. it drives down input resistance (now you need the gamma match) while also driving the frequency up the band, now requiring the lengthening of the vertical element by +or- 5.5" to bring it back down into the band and with the additional loss the swr bandwidth is wider than it should be. it is not well known that as loss resistance increases in an antenna system that the bandwidth will be widened but for all the wrong reasons. claims of ever increasing swr bandwidths mean more Rloss / loss resistance (bad) and less Rrad / radiation resistance. (bad) it all adds up to reduced antenna radiation efficiency and directivity..

 

[HomerBB]

And, so, what would your "improved" antenna look like?
Lotsa words, and interesting, but I am an empiricist. Show us your new improved "improved new Vector 4000", if you don't mind.

 

[freecell]

https://pdfpiw.uspto.gov/.piw?Docid=04282531&homeurl=http://patft.uspto.gov\
https://cb-antennas.com/wp-content/uploads/2013/12/Sigma-IV-1.01-Jan-2015.pdf
https://www.worldwidedx.com/threads...ernative-view-point.31799/page-44#post-765023

 

[HomerBB]

I see some pdf files from a 1981 patent, and Henry's report. Nothing different than what has been around for quite awhile.
Wanted the one you mention in post #661.

 

[bob85]

IF when you sweep the radials up towards the monopole & observe resonant frequency rise while impedance drops necessitating a gamma feed at that radial spacing due to the capacitance between radials & monopole & that increases loss,

Why is it that the 4 radial versions using the same spacing/hoop size have an edge in performance over the 3 radial version that has less capacitance between radials & monopole?

Homer if you space the radials the correct distance from the monopole you can isolate the monopole from the radials like a skeleton sleeve fed monopole & dispense with the gamma,

do you get the compression of the pattern & extra gain talked about in the open sleeve antenna article ? I don't know,

I think Freecells idea of improving the design is to ground mount the 3/4wave monopole over a huge
radial system, which may work for you if you live like a scarecrow in a massive corn field but not if you live surrounded by obstructions in a town/city.

 

[freecell]

you don't improve the performance of any antenna by reducing the lateral and radial dimensions of the antenna. in addition, there's an instant increase in directivity of 3 dB. when any ground plane vertical is ground mounted. see logan and rockway 1997.

24 years ago....

"a comparison involving antenna measurements and performance predictions has sometimes revealed a 6-dBdiscrepancy between the ground-wave transmission measurements and the corresponding calculations. The source of this 6-dB discrepancy is attributable to an incorrect definition of the effective area of the receiving vertical monopie antenna. This erroneous definition is that the effective area of the vertical receiving monople is twice as large as that of a corresponding receiving dipole in free space. This report shows that the effective area of a monopole is one-half that of the corresponding dipole. It is this value of effective area that resolves the 6-dB discrepancy
between measurements and analysis."

Wolf was wrong.

 

[HomerBB]

@bob85, I don't know either..., but it does cause me to want to build another 2m version and try to figure out a way to determine changes in the antenna's performance by making changes to the angle of the radials to the vertical. The 2m version makes it quite easy to get above 1.5 wavelengths high.
@freecell what I've been asking for is a photo of a working model of this antenna you have made with those improvements, and, if it exists, how you substantiated in the real world that those improvements gained the results you anticipated.

 

[HomerBB]

freecell, I tried to read dipoleandmonopoleantennagain.pdf ...
Until the authors start talking in normal terms we hillbillies are going to move on to something simpler. But thanks for sharing.

 

[bob85]

I may be reading the article wrong but it mentions infinite perfect conducting groundplane which is what the 5/8wave proponents use to bolster their claims of gain for a radiator with 1/8wave of deconstructive radiation,

Having a super efficient ground mounted antenna is OK in some situations but its no good if it can't see through buidings & other obstructions for people that live surrounded by obstructions.

According to the arrl antenna books which I quoted in the first post of this thread many years ago
a 3/4wave monopole fed at its base has 1/4wave of out of phase radiation from the lower 1/4wave whereas the open sleeve antenna with its close spaced radials has radiation from the lower 1/4wave that is in phase with the upper 1/2wave compressing the pattern & increasing gain over the simple 3/4wave monopole

The explanation the arrl gives us is that when you bring the radials close to the monopole resonant frequency goes up & impedance goes down,
transmission-line mode currents flow between monopole and radials,

impedance drops because the transmission-line mode impedance is seen in parallel with the 3/4wave monopoles antenna mode impedance,
current flows into that impedance & current flows on the outside of the radials as in phase radiation just like the in phase radiation from the short leg of a J-pole caused by the unbalanced termination of the 1/4wave stub increases gain in the direction of the short leg,

we have not seen any model that shows how much radiation comes from the outside of the cone in the sigma4 because the only model anybody has done is Henry's model that was terminated with resistors & not unbalanced as in the real antenna,

Transmission-lines don't radiate when they are terminated with a resistive load regardless of the load been equal to the characteristic impedance of the line or not,

all we are seeing is a small magnitude of radiation due to the conductors of the cone not been very closely spaced and perfectly parallel to the monopole,

I have asked time and time again if NEC or other software can model the cone in isolation with an unbalanced load replicating the real antenna and thus far nobody has come up with a solution,

Homer why not build a ssfm & compare it to the sigma style antenna,
just make sure you use a quality isolator & not a lossy CB antenna mount like the guy who published the skeleton sleeve fed monopole article,

That would answer how far behind the ssfm a sigma style antenna is if its behind at all.

 

[freecell]

freecell, I tried to read dipoleandmonopoleantennagain.pdf ...
Until the authors start talking in normal terms we hillbillies are going to move on to something simpler. But thanks for sharing.

bob85 posted: "I may be reading the article wrong...."

in 1966 wolf claimed that the effective area of a monopole antenna is twice that of the corresponding dipole. everyone was taught this and bought into it when it was obvious to many that it was erroneous. this went on for 31 years.

in 1997 j.c. logan and j.w. rockway demonstrated that the effective area of the monopole antenna was instead one-half that of the effective area of the dipole.

this was the big news because with equal power applied to both antennas, the antenna with half of the effective area will produce a signal that is 3 dB. stronger than the antenna having twice the effective area.

the 1/4w. monopole is ground mounted and the dipole is tested @ multiple, above ground feedpoint heights.

 

[freecell]

bob85 posted:
"having a super efficient ground mounted antenna is OK in some situations but its no good if it can't see through buidings & other obstructions for people that live surrounded by obstructions."

with maximum directivity @ 45 degrees and a -3 dB. beamwidth of +or- 25 degrees that's not much of a problem. east and west it clears the mountains and it's a level runway to the north and south.

 

[bob85]

That sounds ok for where you live but not good for us here , I am the only person local that has the room to put an antenna over a reasonably large groundplane, it would not see over the obstructions.

interesting article, are these guys partly responsible for mininec ?,

The article also says this,

"The effective area of the receive monopole is one-fourth the effective area of the corre-sponding receive dipole.
Thus, if a monopole and a dipole are immersed in identical fields the dipole will deliver to a matched load four times the power as is available from a monopole",

I have a hard time with models over perfectly conducting infinite groundplanes that don't exist in the real world, that's what got us into the 5/8wave gain over a halfwave nonsense that advertisers use to bullshit money from your wallet,

is it fair to compare a 1/4wave monopole over a perfect infinite groundplane to a free space dipole ?
The results change when the dipole is measured at different heights above the same perfect groundplane rather than free space.

 

[freecell]

bob85 posted:
"The results change when the dipole is measured at different heights above the same perfect groundplane...."

PAGE 25, 26: the receiving dipole antenna is oriented vertically to the ground pane and is situated at various elevations above the ground plane. These elevations are measured from the bottom of the dipole and include 0.5, 1, 3, 5, 7, and 9 wavelengths.

Equation (25) gives a transmission value of-54.7 dB for this configuration. The MININEC
Professional calculation is also -54.7 dB FOR ALL OF THE RECEIVE DIPOLE ELEVATIONS.

"interesting article, are these guys partly responsible for mininec ?"

the original MININEC was written by John Rockway with a little prodding and support from Jim Logan. WB0DGF Antenna Site - Mininec

 

[freecell]

I see some pdf files from a 1981 patent, and Henry's report. Nothing different than what has been around for quite awhile.
Wanted the one you mention in post #661.

the original avanti patent itself tells us no less than three different times how the performance of the sigma IV can be improved but you will have to give up the reduced lateral and radial dimensions to make that happen.

i would direct you to the following pertinent sections of the patent.

https://pdfpiw.uspto.gov/.piw?docid=04282531&PageNum=1&&IDKey=&HomeUrl=http://patft.uspto.gov\

page 3, column 2, lines 47 - 66
page 4, column 4, lines 23 - 36
page 5, column 5, lines 07 - 15

as the acute angles between the "diverging" radial elements formed by the common connection point with the vertical radiator are increased, the directivity of the antenna also increases. avanti tells us in the patent that just and increase of 15 degrees (30 degrees total) can yield an increase of .5-.6 dB. and that "in some instances" directivity continues to increase as the "diverging elements" are moved even further away from the radiator.

post #661 is not from a patent or other internet document, if you want it then copy it. there is no link to it since this is the first place anywhere on the internet where this appears, i wrote it.

 

[HomerBB]

For several years this antenna has caused a lot of discussion, some disagreements, and hurt feelings.
The sides are not just two, but I see three.
1. It is a greatly improved monopole antenna with out of class performance,
2. It's nothing (dismissively), but a fancy dipole, and
3. It's just a half wave antenna and the lower section adds nothing to it's performance.
The result is that a few dropped the discussion because they thought, "I was right all along" although they'd not really provided much to the discussion except it looks like a jpole (Personally, I can not tell a Fiat from a smart car until I see the logo, but neither are each other, they just look alike). Others equivicated on their positions going one way, then swinging the other way, then wobbling back and forth like a drunken pendulum.
While others stood firmly despite the arguments on the empirical results they had gained by deploying the antenna, sometimes multiple times and places, over extended periods of time.
I am one of the empiricists.
Show me.

I read a very interesting antenna article wherein the author extolled the virtues of the antenna in question. He supplied all the data as in measurements, gain potential, etc and told everyone how to make one of their own. Then, at the very end he wrote, "I have not built this antenna myself. If you do let me know how it worked out."
I moved on and did not build his antenna.
Bring me your arguments, and I will bring my experiences.