Base New Vector 4K radiator at 0.75 - 0.82 - 0.875 wavelength.

[Marconi]

Here are the overlays for the EF Vector vs. my S4 and my NV4K.

Bob, I started out with this end fed not working too well with the NV4K model.

I tried making the radials wider and got a nice match but the pattern and gain was no-way-no.

I made the radial offset 5" inches and the model looked better with the pattern, so I tweaked it for maximum gain and it brought me right back to pretty close to the Vector design.

So, not much has changed since the first time I tried making a NV4K with no gamma and end feeding it. Looks like I just went in a circle.

Here we have, an EF 3/4 wave model that shows very good gain at a low angle. But the match, though workable, has a low resistance and showing a little under 2.00:1 SWR at resonance.

So again, I predict that Homer may have some serious figuring to do...in order to get this idea to match better while direct feeding at the end of the radiator...if he's looking for good match at 50 ohms at resonance.

Below is the best EF model I have for now and three overlays comparing it to the S4 and NV4K.

 

[bob85]

Eddie
are the gamma fed models including losses from the gamma match setup ?,

 

[Marconi]

Eddie
are the gamma fed models including losses from the gamma match setup ?,

No Bob. I can't model the physical gamma. I can only simulate it by placing the source at a similar point close to where we see the dog bone located on the real antenna, or at the dimensions noted in the manual for the tap point...like we see in the NV4K manual.

Don't get this wrong Bob. I'm not saying all my models that simulate a gamma always appear to have the source exactly where it belongs. Some of such models have the source set where it provides a suitable match...which is only a goal I might start with.

I won't bother to explain now, but I have thought about this topic of losses, gammas, and other types of matching devices relative to some claims I've heard. So, I can explain even if I would only be speculating.

For years I've heard claims of various matching systems that were more or less lossy. Our I-10K's had great claims made about how less lossy the trombone tuner was compared to all others. Whenever I had the chance I always asked: "...how much difference are you talking about here?" Even though when I asked, I knew that silence would follow.

I modeled the I-10K trombone matching device and saw a difference. I posted about what I saw, but nobody was interested. Anyway, I did not claim that the trombone tuner was a much better tuner...what I saw was a difference in the effects of that big tuner on the pattern...not on the match having less loss. The physical matcher added to the I-10K model did match the antenna. However, in case you didn't know...the I-10K has a terrible match without a matcher. So, there must be a lot of transformation going on to solve that problem. While the S4/NV4K natural match is very close to 50 ohms resistive already, so IMO there should be very little transformation going on with a gamma.

BTW, I asked Jay how much less loss there was on his I-10K compared to his competition...and he had no answer.

Using my modeling and some real world testing, I have tested many times as best I knew how. I was looking for ways I might tell what differences I was hearing reported. I figured if the claims were coming from other's without any numbers to report and for sure their having no evidence either, I figured I was smart enough to duplicate that effort...if I didn't even put my mind to it.

Sometime back when I first did a model of a simple horizontal 1/2 wave dipole and saw all reported numbers produced by Eznec equal or very close to the published scientific data for an unsupported 1/2 wave dipole well into the clear...I knew I could use that as a base-line...so-to-speak.

I probably posted some or much of that stuff...but nobody was interested, not even curious enough to ask questions. I have such a series of models that I never published for Homer. The reason was: a question that came to me when he was talking about a center-fed dipole he once built that stood a couple of feet off the side on a supporting mast. I wondered if the gamma, in that case, made a difference that Homer could tell or if he was even curious. On the other hand Homer might have just consided to use the Sirio 1/2 wave CF dipole to check out. I also remember calling him on the phone and talking about modeling.

Bob, can you tell me how much difference you think there is between a direct-fed dipole and a gamma matched dipole, just to make verification easier.

I would be interested to know your thinking.

 

[bob85]

I don't know how much loss there is in any matching setup Eddie, i don't have a means to measure it,
Heres what w8ji said about gammas,

"The gamma match capacitor can only cancel reactance, it can not modify the "real part" (resistance) presented to the feed line. It is the most simple form of matching, and has the lowest operating Q and loss of any system (when it is useable). Adjustment of resistance (real part) requires adjusting the diameter, spacing, or length of the gamma section".


i don't imagine its as efficient as direct fed but could we see any difference on air ?,
there is a good argument for eliminating the gamma on long term reliability grounds,

you may have issues modeling the gamma as its not parallel with the radiator nor does it use the same diameter tubes as the radiator,

this article gives some info on gamma matching,
http://owenduffy.net/blog/?p=2822

 

[Marconi]

I don't know how much loss there is in any matching setup Eddie, i don't have a means to measure it,

Bob, I don't either.

I'm pretty sure a gamma can match some antennas, however. I've seen it done with my own eyes repeatedly over and over. I've also seen folks that couldn't get a factory pre-tuned A99 brand new out of the box...to show a good match. So, I'm not sure the gamma is lossier than some other matching devices. I may find some merit is some technical writings if I understand, but I have never really been convinced one way or another.

Basically, due to the lack of evidence, I don't find the idea that gammas are lossy...makes a good argument either. You make good sense to me saying you have no means to measure. If so, that is enough for me to doubt the words of others on this issue

In the end I think we might find that there is a slight difference to be noted...but like I said before...when a CB'r hears something that in truth is a very small difference...suddenly the differnece is blow all out of portotions.

i don't imagine its as efficient as direct fed but could we see any difference on air ?,

Bob, this sounds like good common sense opinion to me, but in your experience have you ever noticed a gamma as being less efficient or more lossy...when the same antenna is compared to one with direct feed?

there is a good argument for eliminating the gamma on long term reliability grounds,

Well, that is a mixed bag of experiences for me. I had my homemade 4 element horizontal yagi up for over 10 years straight with a gamma, and no problem. My A/S Sigma4 is poorly designed around the base connection area for the gamma. The wind blows enough here to cause the heavy bottom of the radiator to flex enough to break the soldier connection, the poor design. I fixed that by using a short wire with a hose clamp attached like the old Maco gammas used to for their beams. No problem any more, but that probably was a design problem..wasn't it?

The NV4K uses a stud type gamma connector at the base and that looks more secure than solder to me. However, if the mast ever did flex I might suspect the dog bone connector bracket at the top could move or bend. More design problems, right?

you may have issues modeling the gamma as its not parallel with the radiator nor does it use the same diameter tubes as the radiator,

Based just on the link you posted by OwenDuffy.net...I will not have an issue in modeling a gamma...I will never have enough understanding to model such a device.

In closing, Maco publishes gain figures for the M105 yagi showing 15.5 dbi gain and it uses a gamma match. If you check Henry's 11-5 OWA yagi, that is direct fed, you will see they both report gain that is about equal.

This may not be proof of the issues being discussed here...but we both know we've heard nothing else as proof to the contrary so far.

 

[bob85]

The sigma gamma is a bad design been soldered to the connector with a whimpy ring tag, solder should NEVER be the mechanical strength of a joint,

i cured mine by double skinning the bottom section up past the gamma strap,

common sense tells us if its not there it can't break, suffer moisture ingress, move value, catch snow & ice,

I have never noticed a difference in signal that i thought was due to matching setups on beams, never compared two beams with the same boom length & element count,

years ago I did assemble my lemm hairpin match backwards according to the instructions i found tucked inside the boom when i took it down.

the lemm worked ok assembled wrong.

 

[Marconi]

I have never noticed a difference in signal that i thought was due to matching setups on beams, never compared two beams with the same boom length & element count,

Bob, I haven't made such a comparison with two beams either.

I trust Henry's reported gain for his antenna designs. He publishes the model reports. Maco doesn't do that, but I've modelled several of their horizontal M type beams that use a gamma match...and my results are very similar while I only simulate this matcher. So, I compared the published reports on the gain for both of these 5 element horizontal yagi type antennas, I don't see much difference.

My point here is, there is little to no difference in gain reported for these two antennas...comparing a direct-fed vs. a gamma-fed. IMO, the differences between what science reports and what CB operators report are very often vastly at odds.

years ago I did assemble my lemm hairpin match backwards according to the instructions i found tucked inside the boom when i took it down.

the lemm worked ok assembled wrong.

I took a 3 element yagi down years ago for an old buddy. The antenna was working at the time, but it was bent up. This old man had a gamma attached that he made. The insulator inside the aluminium part was a 12' inch piece of plastic garden hose. I too have seen a lot of things work that shouldn't.

 

[Shadetree Mechanic]

Well Bob, I think I finally did what I promised you a long time ago when I told you I was determined to learn to model with Eznec5 saying, "...I want to try and prove your testing your Vector Hybrid was just like you were telling folks."

Honestly though, I haven't quite done that yet, but I just had to say it. I think however, that I maybe I have proven Donald was right about his 0.82 wavelength radiator idea, but I'm not sure he would be pleased to see such a small difference.

I told you the other day I was not finished and I wanted to try and modify my model to take care of the inductance in the model with my simulation for a gamma match.

Here is Donald's 0.82 wl = 356" inch model that has been fixed just like I thought it might. It shows a modest improvement in gain over my model of the 3/4 wave NV4K model I have set at 323" inches.

The model responded just like I was tuning the gamma match. I could possibly tweak the model to better numbers, but it will not change the gain one bit. I saw the gain staying steady on 4.63 dbi in the final iterations before I stopped piddling.

I'm not sure yet about the 7/8 wl model, but your new info on the radiator length will be helpful in getting started with that model.

BTW, these Vectors models are a close to specs as I can get them. The radials are very close to 107" inches 106.99" inches to be exact. Remember, I'm the guy that always pesters everybody and pisses some off about the specs and the dimensions. I try and do my research on that score too...even if being accurate on dimensions might not make much difference in the end. Maybe 6" inches on your 7/8 wave won't make much difference either.

I'm still waiting on Shade Tree Mechanic to get us his dimensions, so I have another viewpoint to consider.

Bob, you're the man!

I got the antenna up and running and took some measurements. Here is my antenna thread. If any other measurements are needed, let me know and I will tip it down and throw a tape on it. The instructions say to only adjust the gamma rod to tune the SWR. I also moved the dog bone bracket for the gamma rod which seemed to help. Would I benefit by adjusting the radiator length too?

https://www.worldwidedx.com/threads/sirio-new-vector-4000-install.226677/page-4

 

[HomerBB]

I got the antenna up and running and took some measurements. Here is my antenna thread. If any other measurements are needed, let me know and I will tip it down and throw a tape on it. The instructions say to only adjust the gamma rod to tune the SWR. I also moved the dog bone bracket for the gamma rod which seemed to help. Would I benefit by adjusting the radiator length too?

https://www.worldwidedx.com/threads/sirio-new-vector-4000-install.226677/page-4

Possibly. No harm in shortening it an in or two to see where the SWR moves to. It reads the antenna is long by a bit. Of course, without an analyzer to confirm resonance it may move, too.

 

[Oscar Goldman]

I know this is an old thread. But has anyone modeled this antenna at just 18 feet off the ground to the feed point.
I am wondering what the pattern will look like. I am building one right now that will be mounted at that height.
Thanks

 

[HomerBB]

Hello Oscar.
I do not model, but I have used this antenna at a variety of heights and can assure you that your experience with it will be great.
Good luck on your project.

 

[Oscar Goldman]

Finished my build and tested it on the air, works great and is about 2 s-units better than my Astro plane.
Match was perfect with around 49pf of capacitance in the gamma.

 

[Oscar Goldman]

Finished and installed works great. Built a 20kw Teflon Capacitor for it. Built to sigma 4 spec's and added a 4th basket support. Vertical element is larger diameter tubing. Has offset radial hub.

 

[bob85]

That's the prettiest looking sigma clone i have seen thus far, quite a contrast to the fugly vortex version.

 

[Oscar Goldman]

Thanks Bob
Here are some more pictures.
I used Teflon bar for the basket spreaders.