Modified Vector 4000

[bob85]

Donald
there used to be a repeater on 6 not far from me, nobody even uses the 2mtr repeaters,
next time im playing i will try accessing it if its still turned on,

its nowhere near where my antennas are tuned for.

 

[Marconi]

gamma tube 13mm x 225mm
gamma rod 6mm x 540mm exposed to center of dogbone

Bob, doesn't your gamma rod extend a little above your dog bone. I can't explain why, but I find this short length, for the rod above the dog bone, is important to tune with my models too, and sometimes it makes a noticeable difference.

I don't worry about it, because if I think about it, I usually tune it too at the end of the tuning process and I think it makes some difference in the performance, not sure but maybe gain.

DB would be the one to ask about this in modeling.

 

[bob85]

Eddie,
I tried various tube & rod combinations on both antennas,

The 3/8 the gamma rod does extend beyond the dogbone about 100mm,

i will be swapping the rod for a shorter rod later because it looks better, no other reason,

The rod on the 1/4wave cone is cut so it does not extend beyond the dogbone but it did before i swapped the rod,

The rod beyond the dogbone does not seem to make much if any difference to tuning.

 

[Marconi]

Bob, since you gave me your dimensions for the Vector in you dbm project at 50 mhz, I'm making a new model of the NV4K at 50 mhz.

What is your overall length of the antenna from the bottom of the hub to the tip? My Free Space model is 177.95" inches at 50 mhz, and is showing 2.49 dbi gain at 5* degrees...without being tuned. The Average Gain show 0.975 = -0.11db and the gain is understated in this case, so that = 2.60 dbi when corrected.

 

[bob85]

From the centerline of the hub where the radials & gamma attach to tip is 4540mm measured with a tape measure.

im interested to see if Nec can handle the fat monopole & skinny gamma rod & get a good agt.

 

[Marconi]

Hey Bob, I think you missed reading the end of Cebik's article, where he also explained an exception to his claims saying Eznec is not able to effectively model a gamma match. This is in the last paragraph in this block image #5 in his 26 page article.

You missed the part about the use of MININEC being more forgiving of the limitations in Eznec?

Here is what you posted earlier.

Here's what Cebik says about NEC & gammas

"It is possible to construct a series of antenna models to serve as a surrogate for the physical antennas. However, we cannot do the job in NEC-2 or even NEC-4. As suggested in Fig. 5, the gamma assembly presents NEC with two problems. First, unless the gamma and main elements are the same diameter, we encounter angular junctions of wires with dissimilar diameters. Although NEC-4 improves on the performance of NEC-2 under these circumstances, the results are insufficiently accurate for use as a comparator to the calculated values. In addition, gamma spacing is rather narrow for most beams that use relatively fat element diameters. Under these conditions, NEC tends to yield less than precise results. The relative unreliability appears in the average gain test (AGT) scores, which generally are no better than 0.92 when a perfect score would be 1.00. Since arriving at a feedpoint impedance of 50 Ohms is critical to the comparisons, AGT values in the range of 0.92 are too far from ideal to be useful. Values of 0.98 to about 1.02 are more valuable to the task of comparison"

more on modeling gammas & using calculators

https://ea5nd.com/wp-content/uploads/2017/11/Gamma-Match.pdf

Below we see on page #10, in the the PDF file that Cebik had more to say about the problems that Eznec has in modeling a gamma match. Here he also says in part, ".....At best the models are comparators so that we may observe some general trends as well as similarities and differences in outcomes."

The rest of the paragraph you omitted from your post #838 is in the PDF file below. The 1st part of Cebik's comments on page #10 are noted in the "png" file below.

How say you?

 

[bob85]

I don't think i missed something Eddie, i posted the link for anybody interested in what it says,

The part about nec 2 & 4 is just something i noted that could be causing you some issues with agt,
you had a long dogbone that does not work in practice with the tube diameters im using,

The info about stepup ratio with different diameters & spacing told me I needed to narrow the spacing to lower the Z0 of my gamma section,

I flipped the clamp over on the dogbone which sets gamma close to parallel,

& because my 50mhz versions are using relatively fatter tubes than any 27mhz version i decided to start with the longest rod & shortest tube to reduce gamma diameter,

It worked,

If somebody converts a v4k to my dimensions,
places it 1/4wave over average ground & adjusts the gamma capacitor, they will get a low vswr & a wider vswr bandwidth like Vortex claim,

im still waiting to see the extra signal strength,

when you look at their other crazy claims & what happens with widebanded j-poles when you extend the short leg i doubt i will see extra signal but i could be wrong, more tests needed,

its snowing im not messing with antennas.

 

[Marconi]

im interested to see if Nec can handle the fat monopole & skinny gamma rod & get a good agt.

Bob, my short term memory suffers since I had Covid, for sure, and that is why I went to a Neurologist recently and she gave me an old drug that has been around for years. It is hard getting use to, but it helps me with my neuropathy pain due to diabetes, but it gives me headaches. She warned me that I might have headaches...if I've had some mini strokes that I didn't know about. I'm going in soon for more scan testing.

I think the model you saw with a long dog bone was a new model I was making using a Vector model at 27.205 mhz. I likely set the frequency at 50 mhz, at 1st, so I would not forget to make the change and do a lot of work and find out I forgot to change the frequency. I got fed up using the scaling tool. I was trying to change the dimensions to the info that you gave me, and I probably forgot to change the DB length among a few other things too. That probably stump my progress...and I just never found the error until your comment.

Bob, when I do a Free Space model, I do it so I can run the Average Gain Test and keep a track on the accuracy, but it is not easy. Such models have NO MININEC. ie., lossy ground in the model as a result. This is one of the losses that are required to be removed in the case with Free Space models, again this is where all losses are turned off.

So, in this case the MININEC feature is also turned off. It is true, as Cebik noted...that the AGTR is difficult to impossible to manage and see a perfect 1 AG result without the use of MININEC feature tuned on.

When I set the FS model over real Earth and use MININEC the model can be tweaked to show a good match and the gain is often within a reasonable range. It is also possible to tweak out a good AGTR too.

In the case with this Vortex model I was trying to get my model to the accurate dimensions with out tweaking the radiator length. I still doubt it will prove to show the big gain they advertise for the Q82 Mark 2, however.

Bob, I must admit that many of my models are NOT as accurate as I would hope, regarding the dimensions, simply it is hard to get all those important detail to antenna construction. It is also hard to get folks to get all the dimensions needed and the little details are often impossible to determine, so I try to get close.

When you decided to make your 6 meter Vector into a Vortex with the extended cone, I'm sure you did some serious planning to all the important details.

Sometimes I will check out an old model I did several years earlier, and assuming I got some good results...I still find some silly errors I made. That said, I am often surprised after I try and repair such a model, that in the end, the results were very close to the same, in spite of the errors. Tuning sometimes, has a way of covering up little differences.

I'm very interested in your results, so keep me posted on your testing.

 

[bob85]

I don't think you will see the extra gain either but I have to test at about 1 wavelength above ground as they did to be sure in my own mind,

If after more tests i find the 3/8wave is still behind & that i am not embarrased with the ease at which i am able to dx long into the night when all other verticals have falen silent,
I would like to know what they did with the model to make it look so good,

I won't pretend to understand why nec has issues with gammas other than what Cebik says in the link I posted, the other info Cebik gives us worked first time for me,

The only planning I did was deciding to use a broken vector for 6mtrs because my diamond v2000 is shit on 6mtrs,
all I did was scale the lengths & hoop diameter,

I set the gammas up with a stock dogbone & 27mhz tapping point then put a second dogbone on the monopole near where I thought it wanted to be for 50mhz & marked it for cutting & drilling to keep the same gamma angle as the 27mhz versions,
turning the clamp 180 degrees set the gamma close to parallel on the 3/8 cone & fixed the tuning,

been working on the car getting it ready for its MOT between rain & snow with more snow forecast from sunday through next week so its not looking good for playing with antennas.

Good look with the scan.

 

[Marconi]

Bob, here are the Free Space and Real Earth models for the Vortex Q82M2 antenna. I was able to get this antenna tuned pretty close, and the Average Gain = 0.999 = 0.00db error correction.

So, you're right this model is difficult to tune as a model when placed over Real Earth. I think I still did some guessing for dimensions for the gamma and the connection points near the bottom of the antenna.

I also used the scale feature to bring a New Vector 4K to 50 MHz and then I fixed the taper and made the other dimensions.

Concerning the issues about steering the S4/NV4K designs, I also posted what the Roy's manual tells us about Free Space models and the Ground.

So again, I was wrong and it is possible for this Vortex design to steer the take off angle below the horizon, but angles below the horizon can only be demonstrated in Free Space Models.

Roy tells us why in the section I posted below and it makes sense.

This model also clearly shows us a lot more of the bandwidth than Vortex reported. The steering idea that you've told us about is also exposed in my model as well.

Maybe this effect has something to do with the DX you've talked about in your antenna. Plus if you check the antenna view with the current phase turned on, you can see the bottom 1/2 wave cone seems to be producing more RF than the top 1/2 wave radiator just based on the red line noted.

My model's Tabular Currents Log also shows the currents in the top and bottom are in phase, but IMO the antenna looks lossy at the top.

 

[bob85]

I don't buy into the Vortex nonsense Eddie,

I found out more info from owners & ex owners that had issues right out of the box & not only with the Q82,

The 3/8 cone may be steering the pattern, It certainly changes signal strength but not in a positive direction for me & not enough to make much of a change on a typical s-meter,

I don't know what they did to make the model look good, the images are too small to see anything for me,
Whatever they did I don't see it in my tests,

it does give the claimed wide low vswr bandwidth but that's all folks.

I would not have a Vortex given even if they offered to pay my fuel costs for collecting it.

 

[Marconi]

Bob, I know that this China Covid virus can make you crazy. When I went into the Hospital I thought it was over for me and I thought I was crazy. I have a younger Brother that has always been a bachelor, and you would think the loneliness that comes along with that life style and with lock-downs would not be a problem for him, but he is getting treatment right now for paranoia. He says he is stir-crazy.

I'm working on the model I posted above, but now I want to simulated the match. This is where I find a match on the actual radiator itself where I get a close.

All I intend to do is move the gamma wires away from the model about 4' feet and instead...and then locate the source on the radiator, itself, where I can find a close match.

So, don't go stir crazy on me yet, I want to see if I can get this thing to act right, now that I think I've got some dimensions to work with.

 

[bob85]

Sorry to hear about your brother Eddie, he's not alone, plenty of people have cabin fever right now, Im ok, could do with some nice weather so we can spend time in garden.

Good luck with the model,
im not sure what you mean by getting it to work right by putting the source in the radiator,
if you get it to work like Vortex's model, I don't think their model is correct.

 

[Marconi]

Bob, I had a gamma match on the other model. I removed it and re-placed the match on the base of the radiator...just like Vortex looks to have done it. Now the Real Earth model has a band width that will work both 11 meters and 50 meters


I got it to match and I was about to do a Free Space model to check out the Average Gain Test and the dinner bell rang.

 

[Marconi]

Bob, here is the Vortex Q82M2 with a simulated match where I set the match on the radiator instead of on the gamma. I move the gamma away from the antenna in this model I posted above.

Also notice the current pattern for this model with the phase turned-off. You will see the currents in the bottom cone look to be greater than those in the top 1/2 wave.

Do you remember how your Modified Vector responded when you determined that you might be steering the antenna Take off angle?