Modified Vector 4000

[davev8]

Davev8,
My 11 meter extended double zepp antenna is different from the one you have seen which it will remain because I don't want anyone else to have a copy. If your looking to build one you can google it.
Good luck
73
Maverick 233
Southern, CA

HO......that's not very helpful...especially when a big percentage of your own previous posts are asking for help ...so i think unless you have something useful to add to this thread i suggest you don't
...... i am thinking with the very basic mistakes you have made with gain etc that maybe you did not build it. ....the end

 

[davev8]

9212 divided by frequency in MHz. is the length from tip to connector. The cone support rods are 1/4 wave and the entire length around the loop is also 1/4 wave. Adjust the gamma for VSWR, not the radiator length. These measurements have replaced a lot of 1/2 wave side mounted antennas in my field over the decades. Side mounting gives the dipole nearly a 2db advantage on its strongest side. Adding less than 10% more height in order to top mount this design does not add 2db. However, the coverage is equal to or greater than that of the dipole in its strongest direction but, in a perfect omni pattern.

In some cases we even lost a few feet of height when the dipole was side mounted to a mast already at the top of the tower. When you're at least 100 feet AGL on VHF, several feet either way doesn't make a difference, it all comes down to the gain being focused on the distant horizon. While many people test antennas, few have had the opportunity to compare this design against as many unity gain 1/2 wave dipoles, while virtually eliminating all other variables. It is not uncommon for these stations to reconfirm their 60dbu coverage area after an antenna and TPO change in order to insure compliance with regards to adjacent channel interference guidelines they may be subjected to. Just renting that calibrated field strength receiver for the day has cost some nearly $1,000.

A very big thanks for that. hoop and radials are easy to remember at 1/4 wave...is the radiator a little shorter than early on in the tread ?? this works out for 27.5mhz to be less than 28 feet ....i will still use what you say as you are the one with decades of field testing ...is this with the antenna isolated from the mast ? or don't it make any difference...i see modeling 5/8 waves the TOA go up when you model a mast as well

 

[Shockwave]

Different manufacturers have experimented with the length of this design, building models anywhere from 27 to about 30 feet in length on 11 meters. They have obviously noticed the same characteristics I see in field testing, that the length of this radiator is has a bigger impact on focusing the pattern on the distant horizon than other antennas with a single radiation point.

With both the cone and the top section radiating, the length of the whip and cone also controls the phase delay to the top section. Altering that phase delay between the two sections, allows you to introduce "electronic beam tilt". On 11 meters, our antennas are relatively close to the ground in terms of wavelength and these variables in height also determine what length provides the most effective beam tilt and target area for your location.

On VHF, most antennas are usually mounted many wavelengths above ground and that reduces the effect that changes in height have on the take off angle. That also allows one length of antenna to fit more applications than we might see on 11 meters where antenna height is typically much closer to the wavelength in use and therefore, has a larger impact on TOA.

I've honestly never tested the design in the field without a mast or with an isolated mast. What I can tell you is when the antenna is not properly tuned, it will show CMC on the coax and mast. Changes in the length of either one can show changes in the amount of reflected power at that point. Once the antenna is tuned to 50 ohms, none of this is noticeable anymore.

 

[Shockwave]

Another interesting clue as to how the cone functions with RF currents can be noticed in the CST computer model I posted years back. Pay particular attention to the shape of the current node around the 1/4 wave cone. The 1/4 wave radiator always shows maximum current at its base feedpoint with the current steadily reducing over that length.

That is not at all what the computer model is showing in the 1/4 wave cone section of this antenna. Here we have a 1/4 wave radiator that manages to show maximum current right in its center at though it was a 1/2 wave! I can only replicate this current node shape in modeling when the 1/4 wave element is excited with RF from both ends... I have long suspected that this second current is folding over the top of the cone and radiating on its outside surface, in a constructive phase.

 

[HomerBB]

That is not at all what the computer model is showing in the 1/4 wave cone section of this antenna. Here we have a 1/4 wave radiator that manages to show maximum current right in its center at though it was a 1/2 wave! I can only replicate this current node shape in modeling when the 1/4 wave element is excited with RF from both ends... I have long suspected that this second current is folding over the top of the cone and radiating on its outside surface, in a constructive phase.

Shockwave,
At the risk of sounding thick headed, I ask, "Is this antenna you refer to above the VHF that you install with the 1/4 wave cone and Mhz/9212 scale radiator? "
Just clarifying...
Homer

 

[Jay Mojave]

Hello All: Quit a few postings here, good deal.

Going thru extremes to achieve a accurate electromagnetic measurement is not overdoing it, if gets you a accurate repeatable measurement. Then it can be compared to a analytical computer generated electromagnetic measurement.

Yes I have a few piles of antenna parts and such, Masts, Booms, Elements, and such in storage in junk piles 1 thru 4. Attached is a picture of a old bottom 4 element hoop Sigma 4 type antenna that I replaced with better and stronger stuff. It doesn't have to be new and shinny but represent the real thing in size and electrically. Yeah its seen better days but I will clean it up and test it.

Jay in the Great Mojave Desert

 

[Shockwave]

Shockwave,
At the risk of sounding thick headed, I ask, "Is this antenna you refer to above the VHF that you install with the 1/4 wave cone and Mhz/9212 scale radiator? "
Just clarifying...
Homer

Yes.

 

[Marconi]

Another interesting clue as to how the cone functions with RF currents can be noticed in the CST computer model I posted years back. Pay particular attention to the shape of the current node around the 1/4 wave cone. The 1/4 wave radiator always shows maximum current at its base feedpoint with the current steadily reducing over that length.

That is not at all what the computer model is showing in the 1/4 wave cone section of this antenna. Here we have a 1/4 wave radiator that manages to show maximum current right in its center at though it was a 1/2 wave!

Donald I agree with you in the part, where I made bold type above, and especially with the word "always." However, I'm not sure I can agree that what we see here really is as you suggest...that the CST model is showing us maximum current gain right in the center of the 2 x 1/4 wave radials shown as though the cone radials were 1/2 wave radiating elements. Donald there has never been enough CST information on this subject, so I don't know for sure, but I disagree.

I use to think this list of values were (A/m) amperage per meter values like it shows in the image. But, then I got to thinking that 2.37 A/m is a lot of amperage, and instead my Eznec models show the red lines as the values for gain. Understanding, that the farther away the red line is from the radiator the more gain we have and visa-versa.

Eznec calculates amperage per segment for each wire and this information is found in the Tabular Currents Table Report. It is noted in the last image of the PDF file below.

I can only replicate this current node shape in modeling when the 1/4 wave element is excited with RF from both ends... I have long suspected that this second current is folding over the top of the cone and radiating on its outside surface, in a constructive phase.

I have a vague recollection of you talking about this, but I never understood the point or the test with your two sources on a single wire.

Posted below is a model of the V4K with no loop on top of the radials.

Donald, do you have any idea why this CST model has no radial loop on the model?

I had to add 9" inches to each 106.99" inch radial to set the antenna back to resonance. When I did that, it raised the TOA 1* degree with the same 2.37 dbi gain as my Free Space speck model with a radial loop showing maximum gain to the horizon.

Examples for these modeling ideas are in the PDF file below.
1. My model shows the currents on the radials, in red, and is similar to what you describe in your comments at the top.

2. I noted the amperage for the tip of radial #3 at segment #46 showing the least amount of current at 0.01415 (A). I also noted at the base of the antenna for wire #3 segment #1 with the most amount of current at 0.34455 (A) and that is as a 1/4 wavelength should be,

3. I posted the base of the V4K to show the wire #3 at the base of the antenna.

4, Shows the pattern with maximum TOA of 2.37 dbi @ 6* degrees above the horizon.

5. Is an image of wire #3 in the Tabular Currents Report for each of the 46 segments in that radial wire and it shows a current trend like a typical 1/4 wave element.

 

[bob85]

Has anybody figured out how to model the cone with an unballanced load ?

terminating a transmission-line with resistors of any value won't cause radiation, unballance is what causes cmc to flow and radiation to occur,

try it with 2 parallel conductors terminated with any value resistor it does not need to match the line impedance, = no radiation

then flare the conductors, = a tiny bit of radiation increasing the wider the flare


now figure out how to unballance the line by only loading one conductor,
= more radiation due to cmc cased by unballance.

 

[Marconi]

Has anybody figured out how to model the cone with an unballanced load ?

I haven't figured out yet exactly what you really mean above, but Shockwave says he does not use any CMC mitigation features on his installations, if he can get the feed point match at or near perfect.

I recently modeled his idea to check out what Eznec might predict. I also tryed his 9212 / frequency conversion factor that he mentioned to HomerBB...somewhere and a while back.

The 3 overlays that I compared below were 2 models of the 0.75w version. One with and one without a choke. I did this because the model without the choke showed a small amount of common mode currents on the mast. So that suggested to me, if I had included a coaxial feed line in the model...the pattern would likely suffer and RFI could present some problems.

The 3rd model was my idea of Donald's antenna using a tweaked version of his 9212 factor. It worked out to be 6" inches longer than my 0.75 wavelength version without a choke. His model showed me no CMC just like he told Homer.

Maybe one day I will try making these models using a physical gamma match on the model. That way I can get the tap point much closer than using the simulated gamma idea I used here. Bob, I can use the specs you sent with your image and dimensions for the New Vector 4K long ago including the capacitor value you posted. That said, I have no idea what Donald's gamma dimensions are with his longer radiator and I won't be asking him anything about the specs for his production antenna.

Below are these 3 overlays, and I noted the radiator lengths for each model including Donald's calculated length for his 0.82 wave antenna.

Bob, get me a EZBob image of the idea you talked about above, OK? Pictures work better for me.

 

[bob85]

Eddie,
antenna match won't cause cmc or eliminate it, cmc is a ballance issue,

i have no paint on this pc to draw Eddie, it would make explaining what i mean easier no doubt,


what i mean above is you want to model the lower 1/4wave on its own without the vertical element above the cone to see if it really does radiate,

if you put resistors across a transmission-line it won't radiate regardless of how bad the match is unless the conductors are NOT perfectly parallel,

you can do a simple test yourself in the real world to prove it with coax or ladder line and resistors,

so why does the j-pole leg radiate? because its unballanced,

one side sees the end impedance of the upper 1/2wave while the other sees a higher impedance air,

it will not radiate if you cut the upper 1/2wave off & terminating the top end with a resistor won't fix it,
to make it radiate you need to make the conductors not perfectly parallel so the fields are not fully cancelled or unballance the load, or unballance the source placement,

the same applys to the vector,
you have some small radiation due to none parallel conductors,
but thats not what we want to see,

if you want to see the radiation caused by cmc on the outside of the cone rather than radiation due to none parallel conductors you must unballance the model by terminating the center conductor & leaving the hoop terminated with air,

if you cannot do that i don't think you will ever see radiation due to cmc when modeling the lower 1/4wave with eznec.

 

[Marconi]

Bob, is your idea above suggesting that Henry might have modeled the test wrong showing the cone radiating?

 

[Marconi]

Bob here is my model without adding any resistors at the top. So, the SWR is >100:1.

The antenna image and the currents look very similar to Henry's model that was matched with resistors simulating the presence of the top 1/2 wave radiator.

 

[bob85]

Thanks for having a go Eddie,

if you look again at what Donald said, it may not be the match but getting the cone the right length that minimises cmc,

its not the match,

im in no position to say Henrys model is wrong because i don't know how nec works with regards to how the resistors are connected,
to me it looks like a resistive load connected directly across the end of a 1/4wave transmission-line,

if that is a literal depiction of resistors connected across the end of a transmission-line it won't cause radiation due to cmc on a 2 wire transmission-line,
all you would see is radiation due to the conductors not been parallel, which won't be much at all,

i don't know how you model that setup without the vertical but it won't do something that won't happen in real life otherwise NEC would be useless,

afaik the resistor must simulate the end impedance of the upper 1/2wave while the top of the cone sees air to have the correct unballanced load, can nec do that ?

edit,
your model is also ballanced Eddie, it will only radiate due to the none parallel conductors afaik,
the model must fit what happens in real life with transmission-lines to be of any use in showing what we want to see,, and both yours and Henrys do imho but they are not unballanced as in the real life antenna,

maybe start with a j-pole & look at cmc, remove radiator & look at radiation from parallel 1/4wave stub, then add resistor across end, still no radiation,

then add resistor to only one side & connect other side of resistor to something maybe a virtual ground, i don't know if thats possible or would work,

maybe you do need a real TL model in nec to see any radiation due to cmc,

im sure somebody must know how to model unballanced transmission-lines in NEC.

Thanks again Eddie,
i wish i could be of some help with Eznec but i can't, i only have transmission-lines and resistors to play with.

 

[Marconi]

Bob, I attempted to duplicate Henry's model below. I could only get close, and it made no difference to the pattern or the currents as best I know.

1. is my earlier model with no top !/2 wave and no matching like Henry did in his test of your idea.

2. is my attempt to model Henry's Idea with the top having resistors that simulate his near perfect match. I see little to no difference even with the 3.752 SWR mismatch in my model which shows -35 db gain. The antenna image and currents are basically the same, and look perfectly normal for a 1/4 wavelength element. I see basically the same in the CST model for the cone.

I also see the idea of the cone being coaxial in effect, but I don't see what appears as CMC current and I sure don't see the current on the radials appearing to be producing a 1/2 wave shaped pattern like I've heard mentioned before.