Modified Vector 4000

[Marconi]

Hey Bob or SW how about a little description of what we're looking at. This looks very similar to what Henry sent Shockwave originally. Henry indicated to me that the radiator in that case was only 24' feet long. I didn't get how that was possible, especially in light of the fact that HomerBB told us that his 5/8 wave length antenna with radials slanted up would not match at all in a similar configuration.

No body is even speculating what is going on with any of these models and I don't get much just looking at pictures.

I was waiting on Henry to redo his model of the Vector 4000 with more accurate dimensions before saying anything, thinking maybe a better fix on the measurements would show something to compare with his 24' foot model.

Now we get this model from SW with no description of what it is, and it looks about the same as the first model Henry made. The only thing I can tell is the frequencies are about 20 channels different and the gains shown are basically the same values. If SW tweaked the model that Henry sent him to make the radiator longer and whatever else he did to make it more accurate, then it didn't make much difference in gain and the frequency went the wrong direction for adding length to a radiating element. If this is the best example of the highest gain model from SW, then we don't need a 28', 29', or a 31' foot radiator. I don't get it.

HomerBB modified his 5/8 wave the other day to a Vector style and he indicated that the antenna would not tune until he added the necessary length a bit longer than 27' feet---and maybe that makes sense. However, I thought it was strange when considering that Henry's model at 24' seemed to show good gain and an almost perfect feed point condition at 34.6 + j 0.5289 ohms---a condition with a potential for a good gamma match. The match he showed with the 24' radiator could be direct fed like we might expect with a resonant 1/4 wave radiator.

HomerBB also said his match only went below 1.5:1 SWR when he added the hoop and I don't get that either. Seems I recall the patent saying using full 1/4 wave radials would work fine, but adding the hoop and making the radials a bit shorter also improved bandwidth. I did have a thought that maybe Homer didn't look up and down frequency much to see what was going on elsewhere. But, could this length thing be another point for confusion?

Homer asked for help in understanding of what he was seeing, so I'm inclined to believe he experienced what he described, but I don't understand it---and for sure if I consider how this all is relative to the Eznec models we've seen so far.

We all know how complicated the Sigma 4 design is and thus far there is nothing made clear here until we know what we are looking at. Just keep up the good work and maybe this will clear up soon.

A while back I complained in a previous post I was confused, "I'M STILL CONFUSED."

Here is what Henry sent me stating it was the file that he originally sent SW.

 

[HomerBB]

I appreciate the interest in my queries and do regret I didn't get more info along the way. Right now the feed point is about twenty-six feet above ground, but only ten feet above the roof of the house.

I just checked SWR from 25.165 through 28.755.

28.755 ---------- 4.0:1
28.305 ---------- 3.5:1
27.855 ---------- 2.0:1
27.405 ---------- 1.4:1
27.205 ---------- 1.2:1
26.955 ---------- 1.0:1
26.505 ---------- 1.3:1
26.055 ---------- 1.6:1
25.605 ---------- 1.8:1
25.165 ---------- 1.8:1

I could have gone 10Kz higher, but I doubt it would have mattered. That's as low as I can get with my DX88HL. I was keying in 6 watts throughout the checks. I tried to get the SWR curve to move upward in the bands, but had no joy on it no matter how I worked the gamma match. The curve suggested to me that I might get the shift if I physically shortened the vertical some, so I tried to achieve that with moving the strap on the gamma back toward the feed point. Didn't get me there.
That is why I asked if anyone thought increasing the diameter of the four radials and the ring might affect the antenna. I realize that the diameter of the center vertical has some influence, but I'd have to use a street light pole to get it any bigger. I'm already where I should be going from 1.25" to 0.5" bottom to top.

Perhaps the weather will permit me to make the changes tomorrow to the four radials and ring. If so, we'll see.

The thing works. I could bore folks stiff typing in all the DX stations I've spoken with both on AM and SSB with the antenna.

Perhaps there is some clue in what I've written here for the smarter, better equipped among you to see.

The only locals I've talked to are way too close to help. I can put 10+ on them off my shoe laces. . .

 

[Shockwave]

Marconi,

I think there are two reasons Henry's model shows a 24 foot radiator. EZNEC considers the portion of the main radiator below the gamma tap point to be a separate conductor. It's length is about 1.6 feet and needs to be added to the total main radiator. When you count the total length from the grounded connector bracket to the tip of the main radiator it's closer to 27 feet.

My changes to Henry's model are basically changing the cone dimensions to fit the new Vector. When Henry did his model he did not have the actual dimensions of the antenna. I'm very impressed with the model he made because it's gain is .02db higher then the new Vectors actual measurements produce. No changes I've made have effected the wonderful radiation pattern the antenna produces. They do effect gain and VSWR.

What I see is the when you lengthen the main radiator you have to move the gamma tap point up and the generator source to the same point. This also causes the minimum current point shown by the dip in the pink line to move upwards. Notice in the model that radiation currents are shown in pink with a separate current in phase coming from the base. Maximum gain occurs when the top of the radials and loop are placed right inline with the minimum current point. So they too should be lengthened with the main radiator.

I'm a Sirio distributor and I know they keep all of their box sizes at 56 inches long so they can be stacked on pallets and placed in containers. This means that the maximum size they can make the radials in two pieces is about 106.5 inches and still have a little overlap at the seam. Modeling shows that more gain can be had with a little more radial length. Expanding the loop diameter like I originally did, reduces gain.

What shocked me most about the computer model of this antenna was seeing a real radiation pattern for the first time ever. It shows why the antenna is a great performer for both line of sight and sky wave propagation. The radiation plot shows that the primary lobe actually consists of two major lobes. One centered at 8 degrees above the horizon and a second centered around 21 degrees. They combine and form a uniform signal (+/-3db) from 4 degrees to 27 degrees above the horizon. The lower angles are ideal for line of sight while the range of other angles will fit varying conditions of sky wave propagation.

I think Homer had to add the loop to get a good VSWR because his radials were not long enough to match without the loop. The radials and loop also play a part in the resonant frequency of the antenna. He surely could have found a length and angle that would match without the loop. We should also expect there will be some differences between the ideal computer model and the ideal antenna. For example the model suggests larger diameter main radiators will destroy the gain while real world tests prove it has much less impact. The model shows more gain with the radiator shorter then field tests do.

On the other hand the model shows more gain with longer radials. That is true and probably why Sirio lengthened them. The model gain at 5.55dbi is only off about a half db from Avanti's claim of 6.14dbi. The test equipment from 30 years ago probably had a +/- 0.5db tolerance.

 

[Marconi]

I appreciate the interest in my queries and do regret I didn't get more info along the way. Right now the feed point is about twenty-six feet above ground, but only ten feet above the roof of the house.

I just checked SWR from 25.165 through 28.755.

28.755 ---------- 4.0:1
28.305 ---------- 3.5:1
27.855 ---------- 2.0:1
27.405 ---------- 1.4:1
27.205 ---------- 1.2:1
26.955 ---------- 1.0:1
26.505 ---------- 1.3:1
26.055 ---------- 1.6:1
25.605 ---------- 1.8:1
25.165 ---------- 1.8:1

I could have gone 10Kz higher, but I doubt it would have mattered. That's as low as I can get with my DX88HL. I was keying in 6 watts throughout the checks. I tried to get the SWR curve to move upward in the bands, but had no joy on it no matter how I worked the gamma match. The curve suggested to me that I might get the shift if I physically shortened the vertical some, so I tried to achieve that with moving the strap on the gamma back toward the feed point. Didn't get me there.

That is why I asked if anyone thought increasing the diameter of the four radials and the ring might affect the antenna. I realize that the diameter of the center vertical has some influence, but I'd have to use a street light pole to get it any bigger. I'm already where I should be going from 1.25" to 0.5" bottom to top.

Perhaps the weather will permit me to make the changes tomorrow to the four radials and ring. If so, we'll see.

The thing works. I could bore folks stiff typing in all the DX stations I've spoken with both on AM and SSB with the antenna.

Perhaps there is some clue in what I've written here for the smarter, better equipped among you to see.

The only locals I've talked to are way too close to help. I can put 10+ on them off my shoe laces. . .

Homer, don't cut yourself short, I know guys that bought kits and could not put them together and you built your's from scratch.

You have a great BW at nearly 3 megs and Bob will tell you that his modified Vector showed added BW along with increased gain at a distance. I'm not sure if I would mess with it yet. If you change the radials diameter you will also have to shorten them as well and that does not sound like easy work to me up there on your roof.

Shockwave has worked with his Vector lately, maybe he can advise you which is the best way to change frequency on this antenna. If it was me I would try the tip first, and then tweak with the gamma. If you study the frequency change chart noted in the Vector mounting instructions you should get an idea of what affects what and how much.

You have done good and that is a lot of work. Thanks

 

[Shockwave]

Homer,

To move the resonant frequency up, you usually have to move the gamma strap (tap point) up higher on the main radiator and away from the connector. This places less length above the gamma feed point and increases the frequency. You may also have to adjust the capacitance of the gamma by sliding the inside tube in or out of the outside tube. Does your gamma match consist of two tubes that slide into each other with an insulator between them to form a capacitor? Did you ground the base of the main radiator once you removed the coil from the insulator of the 5/8 wave? There is also the chance the main radiator is just too long. First step that should be easy is to move the strap between the gamma and main radiator upwards a little and check the VSWR.

 

[HomerBB]

Homer,
To move the resonant frequency up, you usually have to move the gamma strap (tap point) up higher on the main radiator and away from the connector. This places less length above the gamma feed point and increases the frequency.

Yes, I tried this. The SWR began to climb everywhere rather then sliding upward. I am willing to attempt this again as it is as you've said, the easiest thing to do.

You may also have to adjust the capacitance of the gamma by sliding the inside tube in or out of the outside tube.

Tried this, too. Ultimately, I kept having to bbring all the adjustments back to where they are now for best all around SWR.

Does your gamma match consist of two tubes that slide into each other with an insulator between them to form a capacitor?

Yes. One or them consists of two tubes, the other of an outer tube and an inner rod. Both have the inner and outer components insulated from each other.

Did you ground the base of the main radiator once you removed the coil from the insulator of the 5/8 wave?

This one I would have to go back up on the roof to check. At one time I had done this, but am not sure whether I kept it that way or not. I am reading this that you mean the main radiator should have a physical connection to the four upright radiators. If so, more than likely it is not done that way. The photos/wording of the antenna instructions appeared to have everything in direct contact with each other, but I doubted that to be true. Seemed odd . . . somebody please clear this one up for me. . .

There is also the chance the main radiator is just too long.

This would be too easy to remedy, but I was concerned with the length not being within the parameters discussed by the folks who have greater knowledge than I have. I wanted it to be more than a look-alike, Dimensionally correct is/was important to me. I was going for an antenna in the 3/4 to 7/8 wavelength range. This seemed to be where the discussion centered. At 27' 11" it is just in there. The length ranges seemed to center around 27.5 to 29.5 feet. more than 5" shorter and my results would not reflect those I was hoping to emulate.

First step that should be easy is to move the strap between the gamma and main radiator upwards a little and check the VSWR.

Yes, I tried this.

Lacking the technical skills of many of you, I just read and then use the material you guys post to attempt to put the physical components of an antenna together. My only artillery in my arsenal is an SWR meter, and/or a field strength meter.

Thanks for replying. All of your questions read like a preflight checklist and have me working my way back through what I done. I'll double check each one of them against the antenna.

 

[HomerBB]

Homer, don't cut yourself short, I know guys that bought kits and could not put them together and you built your's from scratch.

You have a great BW at nearly 3 megs and Bob will tell you that his modified Vector showed added BW along with increased gain at a distance. I'm not sure if I would mess with it yet. If you change the radials diameter you will also have to shorten them as well and that does not sound like easy work to me up there on your roof.

Shockwave has worked with his Vector lately, maybe he can advise you which is the best way to change frequency on this antenna. If it was me I would try the tip first, and then tweak with the gamma. If you study the frequency change chart noted in the Vector mounting instructions you should get an idea of what affects what and how much.

You have done good and that is a lot of work. Thanks

Thanks for the encouraging post. I enjoy doing this, and your kudos make me feel less like a bumbling fool.
Going onto the roof is not too difficult, and as long as the wind cooperates it isn't too hard to lay the antenna over to do some things where it is now. It is much harder when it is mounted to the pole against the side of the house. That waits for when I'm satisfied with the antenna and want to leave it alone.
As you can see, Shockwave has given me some good material to work from. Thanks to the both of you.

 

[HomerBB]

Marconi,

I think Homer had to add the loop to get a good VSWR because his radials were not long enough to match without the loop. The radials and loop also play a part in the resonant frequency of the antenna. He surely could have found a length and angle that would match without the loop. We should also expect there will be some differences between the ideal computer model and the ideal antenna.

You are correct about the length of my radials. They were each short by about 3" as I recall. It is a simple thing to correct, I think, if it is critical I can do it. What concerns me is that I read that the radiation pattern of the radials was not as consistent without the ring showing slight nulls between the four radials. ?
I can easily lengthen the radials and use a non-conducting ring to kept the radials sturdy. Is this something I ought to do?

 

[Marconi]

Homer,

To move the resonant frequency up, you usually have to move the gamma strap (tap point) up higher on the main radiator and away from the connector. This places less length above the gamma feed point and increases the frequency. You may also have to adjust the capacitance of the gamma by sliding the inside tube in or out of the outside tube. Does your gamma match consist of two tubes that slide into each other with an insulator between them to form a capacitor? Did you ground the base of the main radiator once you removed the coil from the insulator of the 5/8 wave? There is also the chance the main radiator is just too long. First step that should be easy is to move the strap between the gamma and main radiator upward a little and check the VSWR.

Homer, I would caution you to not get hasty and make a bunch of changes to your antenna until you have recorded good measurements for ever little thing right where it is now.

Again, I suggest you check out what the Vector manual says about adjusting L1, L2, and L3.

I don't want to confuse you with my words, but if I read SW's remarks above correctly, I think I disagree with the direction he has suggested, and so does the Vector Manual the way I read it. IMO, the Manual clearly says to shorten the space between the tap point and the feed point, just like you shorten the top element, to go up in frequency. I can't be sure, but maybe SW just made a typeO using the words, "..."up higher" on the main radiator and away from the connector." I figure connector means the feed point in this case.

Again, I don't think I would try to adjust frequency by tuning the gamma first. I would tweak the tip a bit with 1 or 2 adjustments and see if the resonant frequency goes up or down. I'm not sure I remember what Bob said about frequency when he was super tuning his modified Vector for gain by making the radiator longer, but maybe he is the one to ask and confirm this issue.

 

[HomerBB]

Sounds reasonable. I did notice the possible conflict between the move up and move down statements. What I wondered was whether the Vector instructions referred to the strap on the inner rod, and SW referred to the point on the outer tube where the feed was attached to the gamma. I wasn't wanting to find a discrepancy, but perhaps a difference. After all, the store bought version appears to permits sliding the radials and gamma match up or down together along the vertical element.
I was under the impression that moving the tap point on the inner rod of the gamma closer to the bottom of the antenna would result in an electrical shortening of the verticals length as opposed to actually shortening it physically. So, like you, I pondered the seemingly two opposite points of view on this.
What I did experience is that moving the strap on the inner rod away from the bottom of the antenna gave me very high SWR, such as I could not adjust out by moving the inner rod either in more or out more. The SWR would move a little, but not improve in the manner I needed. This condition is what led me to ask about the effects the diameters of the radials and ring might play in the frequency range as well as overall performance.

?

 

[HomerBB]

If these questions have answers I could use them.

If not, I'll have to get them empirically and offer them anecdotally.

1 Does the main vertical element have a direct physical ground to the four radiators/coax shield?

2 Does the location of the feed point on the gamma need to be at the same location as the bottom of the radiators with the angle away from the main vertical? (all my experience with gammas say 27Mhz distances are about 4" along the entire length of the gamma.)

That will do for now.

 

[Marconi]

I'm gonna' just watch for a while, this is too complicated for me.

 

[HomerBB]

I'm gonna' just watch for a while, this is too complicated for me.

Now that's funny - "this is too complicated for me" :laugh:

I am the least knowledgeable here. I'm listening to everything you've said. I won't mutilate the antenna. I can always reverse any changes should I make them.

 

[Shockwave]

I can assure you that if the antenna is resonant at one frequency, moving the gamma tap point up will raise the frequency. The reason this seems to be in contradiction to the Sirio instructions is that they have also shortened the top of the antenna when they move the strap down. This has a bigger effect on resonant frequency. They made two changes there. What I'm saying is if you just move the tap point up on the radiator it will raise frequency if that was the only variable.

The main radiator should also be grounded at the base where the radials and coax meet. This could be your entire VSWR problem. The location of the coax connector and bottom of the radials should be as close as possible. The angle of the gamma is not as critical unless you start to hang it far outside the loop. Then it can radiate and throw the pattern off a little.

 

[HomerBB]

ok. Thanks. Clears that up quite a bit.