Any Astro Plane Fans ?

[Marconi]

I know you have trouble reading copies of my notes, but here is what I got raising and lowering your models antenna mast inside and below by 5" inches at a time.

The answer to your question is YES the angle does change on making the mast longer below the hoop, but it is not much and if I changed the overall height of the whole antenna, this range of small changes in angle might not show up at all at some heights for the antenna.

 

[Marconi]

Bob, this reducing of the flare, do you know whether that is pulling the upper part of the legs closer where the cross piece is, or reducing the diameter of the ring, or both?

Homer I know you asked Bob this question, but I use to think, based on pictures of the Avanti A/P, that the radials were just one piece of tubing and the mast insulator bracket would slide up and down near the middle of the two radials and change the arch and maybe tune the antenna. If that is so with the antenna, then I will leave the answer to Bob.

But if there are two radials that this bracket supports in the middle of the radials...then no tuning is provided. One can certainly move this bracket, but that would have to be a modification.

Let me know which way it is and I might have more to say, but Bob is the man for this.

 

[bob85]

i was thinking more like 4ft and 2 ft of mast below the hoop eddie,
i think we already saw waveriders setup with the isolator up near the hoop or thereabouts,

moving the fiberglass rod up and down will alter the bow and impedance eddie,
id expect it to drop if you move the rod down,

can you alter frequency to see if the antenna is resonant somewhere in the band?

 

[Marconi]

i was thinking more like 4ft and 2 ft of mast below the hoop eddie,
i think we already saw waveriders setup with the isolator up near the hoop or thereabouts,

moving the fiberglass rod up and down will alter the bow and impedance eddie,
id expect it to drop if you move the rod down,

can you alter frequency to see if the antenna is resonant somewhere in the band?

I did the 4' foot thing earlier. I guess you missed it, and that might be because I'm trying to be brief, I know you don't like my being wordy.

Bob, the rest is all Greek to me. Wavrider, bow, move the rod down..........what?

 

[HomerBB]

We experimented with moving the spreader bar on my AP months ago. It seemed to have little effect on the MFJ-259b readings. I'll try to find that and see what the analyzer said about it.

 

[Marconi]

Bob, I'm going back to using lots of words again.

If anybody wants to see the real picture that I've tried to describe about the bad acting currents on the A/P, then look at this picture of the antenna and check out that the currents on the mast are in perspective are almost 25% as much as the currents flowing on the antenna itself in their first segments, and this might even be more if were could really consider all the currents on each element.

BTW, just in case you miss it...there is no isolation in this model.

What we see here are currents indicated on the mast that do not show up well, at some angles, when we are looking at a two dimensional image...in its best of 360* degree angles that we might view...in a three dimensional object.

The only way we are likely understand what is really going is to check out a the segment level for the elements. And with Eznec...I can see this in the tabular currents log if the model follows some simple rules for construction. BTW, this does not mean adding extra wire to a model simply to see current flowing. Somebody in your group got that idea all wrong and lead you astray.

We are just lucky that Roy allows to model randomly and with disregard for the rules that NEC requires. I've tried to explain this to no avail...as best I understand it. However I not so vain to say I 100% correct either, it is just what I think I understand seeing as I'm totally self-taught with this stuff.

No body I've ever talked to about this program has ever really been forthcoming with me on the subject of currents, even Roy Lewallen himself, but I understand him and why. I find that most folks always want to get off into their ideas, and close me out in this area. I understand this, but I have my ideas too and I don't think I'm a loon for doing so.

I'm seeking better understanding in this area too, but it is a very technical subject to say the least, so I do the best I can...and sometimes it takes a lot of words...and even then I'm never sure I made my point, right or wrong.

All I ask is that you just give me a chance to explain, and I will talk...even if we disagree.

The currents you see on the mast are at 1> ampere at the first segment of the radiating wire #10 amp in this example where they are the strongest. The current at the mast where the dot for where you plan to isolate shows .24> amperes and that is why I see trouble if you try to put a little power into the antenna.

 

[Marconi]

We experimented with moving the spreader bar on my AP months ago. It seemed to have little effect on the MFJ-259b readings. I'll try to find that and see what the analyzer said about it.

I find the same Homer, but when I consider what the high tech world is really saying...I always figure the difference they're talking about...are miniscule compared to what we CB operators do.

 

[Marconi]

We experimented with moving the spreader bar on my AP months ago. It seemed to have little effect on the MFJ-259b readings. I'll try to find that and see what the analyzer said about it.

I haven't done this on my real antenna, but I did it with my Ezned model and what differences I saw were small compared to what I had on my mind at the time.

This like my grampa use to tell me: when a guy tells you a fish story...just cut the size of the fish in 1/2, and then you might just be close to the truth of the matter.

I could be wrong Homer, but what I think I saw was the frequency changing, and that looked like the antenna match was changing. I was also making Eznec readings right at the feed point, and that might have made some difference too.

Homer, could you tell me if the original Avanti A/P's radials are one piece, or are they two elements like my Old Top One knockoff?

Mine has two pieces for each radial, they are swagged at the ends so they fit together as one piece, and the hard ware bracket actually secures these to elements together...so they can't be moved simply.

Thanks for doing that check and telling us Homer.

 

[bob85]

when i said move the rod im talking about the same thing you are eddie,
sliding the fiberglass spreader rod up and down alters the amount on bow in the radials and alters the spacing, it must alter impedance too,

i think we already established you only need to add the extra wire when you are including a coaxial feedline in the model and want to show any radiation it may have,
and that MOM can handle differential or transmissio-line and common oe antenna mode currents in the antenna model,

are you saying you think putting the isolator about 1/4wave below the hoop will cause issues eddie?
there can't be that magnitude of current there if the mast is isolated,

about 1/4wave below the hoop looks ok unless you can find a better place,

i thought you were trying to establish if changing the mast length from 1/4wave below the hoop to shorter than that like waverider has his isolated without changing the antenna height caused takeoff angle to rise like i think the patent claims,

clearly without isolation some mast lengths will encourage rf to flow on the mast and some won't depending on the length and if they are connected to ground or not.
but what's the best place to isolate if you don't have the luxury of a good mast length for low current to start with.

 

[bob85]

hello Homer,
when they talk about reducing the flare i take that to mean reducing the size of the hoop and re-spacing the legs to return to 50ohms,

all you could easily move with the astroplane would be to pull the legs closer in to less than 12" spacing due to the two piece legs been fastened together and to the spreader in the same way the sigma4 hoop fixes to the radials.

 

[Marconi]

are you saying you think putting the isolator about 1/4wave below the hoop will cause issues eddie?
there can't be that magnitude of current there if the mast is isolated,

about 1/4wave below the hoop looks ok unless you can find a better place,

Bob, I think you are right in you ideas for where the isolation spot should be, but my idea is based only on Eznec modeling. We need to test this idea in the real world, and I believe you can do that.

My model looks like a spot 103" below the hoop is good to go and that makes the mast inside of the antenna and below the hoop 16' feet long. If that doesn't work then maybe you will have to try something closer to the hoop. I'm not sure anything will stop or minimize these currents on the mast enough where this antenna is no longer a problem. That said, if I lived out in the country...I don't think I would care unless it disrupted stuff in the house or shack. Do you have a means to tell at your home?

i thought you were trying to establish if changing the mast length from 1/4wave below the hoop to shorter than that like waverider has his isolated without changing the antenna height caused takeoff angle to rise like i think the patent claims,

Bob, I do recall ever touting that I could control the TO angle of any antenna by tuning or any other way...other than maybe by raising it up higher or making it lower. That said and within reason, I don't think it will be easy to tell anyway...just using my radio.

I know that Avanti talks stuff like that...but again I say when folks talk technical stuff like this...they tend to make a big deal out of a very small difference...one that I would likely never be able to tell or measure.

If I was suggesting something about your needing to isolate close to the hoop like wavrider discussed...I must have been in one of my spells I have occasionally . I don't know anything about wavrider's idea on this subject. I recall that Needle Bender reported he talked all over locally just fine and worked DX all over when he put his isolator right at the hoop, but my model shows that to produce very bad results. Only your testing will confirm if your idea works or not.

clearly without isolation some mast lengths will encourage rf to flow on the mast and some won't depending on the length and if they are connected to ground or not.
but what's the best place to isolate if you don't have the luxury of a good mast length for low current to start with.

I don't know, but Eznec looks to agree with you.

when i said move the rod im talking about the same thing you are eddie,
sliding the fiberglass spreader rod up and down alters the amount on bow in the radials and alters the spacing, it must alter impedance too,

You are talking about Homer's question now, I did not get that until just now.

i think we already established you only need to add the extra wire when you are including a coaxial feedline in the model and want to show any radiation it may have,
and that MOM can handle differential or transmissio-line and common oe antenna mode currents in the antenna model,

Bob, this is tempting and I am surprised at your comments here, but I've promised myself not to discuss my views on the S4/Vector for a while...at least until I can come up with a better way to present my case. I have talked to some guys on eHam, but they were not too interested in discussing this design.

I wonder why?

 

[Marconi]

hello Homer,
when they talk about reducing the flare i take that to mean reducing the size of the hoop and re-spacing the legs to return to 50ohms,

all you could easily move with the astroplane would be to pull the legs closer in to less than 12" spacing due to the two piece legs been fastened together and to the spreader in the same way the sigma4 hoop fixes to the radials.

Bob, I didn't consider that thinking when I did my testing using Eznec. With having to make a hoop with 30 or more very small wires...that would be a booger too test...but you could be right.

I think I recall Avanti saying something about having the radials straight and doing something special, but like Bob says they are prone to puff about their products. I don't remember anything more except with my model it messed it up, so I figured the idea was no-way-no and just technobull.

I had the thought, however, that the top bracket was in a special relationship with the bottom hoop, and these two had to be within a close range to be effective in the functions they perform. Of course I see this setup similar to the S4.

I've said this before, but I recall both Homer and Booty Monster discussing issues with tuning of their homemade versions of their Vectors, and them also discussing the gamma match problems at the same time. I don't know what Homer has to say here, but I recall BM having his radials flatended-out and attached directly to the radiator. I told him that his problem might not be the gamma. I also told him what I thought, and he did make changes in this area. I asked BM to discuss this several times, but I never heard anything after that...one way or the other...except that the antenna worked.

We've hear discussions about limitations with close angles relative to using Eznec, but I would not be surprised if this situation and the S4 design are not closely related and these close angle effects are also in the real world.

I've always made a hub bracket in Eznec for my Sigma4/Vector models, and because I make the hub, I don't get the critical error messages that I know can happen using this NEC product. I've also done the same with my Starduster model, and adding the hub does seem to add something a little different to my model.

This is speculation, and I could be wrong.

 

[bob85]

im getting those two mixed up eddie, yes Needle Bender,

does that mean EZNEC agrees with what i think avanti tell us about not using a mast shorter than about 9ft below the hoop or the pattern can be skewed upwards ?

your gain-master works eddie why would isolating not work on the astroplane ?

i don't recall you saying you could control takeoff angle other than raising the antenna either ,

i have no idea if there is any truth in the claim a 10-15 degree downtilt can be had by removing the flare in the legs,
its claimed in the patent and says the downtilt may be of some use,

who knows why the Eham guys don't want to talk about the vector ,

what diameter masts are you using in your models ?

 

[HomerBB]

Homer, could you tell me if the original Avanti A/P's radials are one piece, or are they two elements like my Old Top One knockoff?

Mine has two pieces for each radial, they are swagged at the ends so they fit together as one piece, and the hard ware bracket actually secures these to elements together...so they can't be moved simply.

Thanks for doing that check and telling us Homer.

The original AP uses two pieces for each down leg of the skirt.

 

[Marconi]

im getting those two mixed up eddie, yes Needle Bender,

That's alright Bob.

does that mean EZNEC agrees with what i think avanti tell us about not using a mast shorter than about 9ft below the hoop or the pattern can be skewed upwards ?

I did some models where I raised and lowered the mast by 5" inch increments, and it showed that the Avanti folks were correct, but the difference was like 1* degree over 20" inches of iterations at 5" inches each. I also made the mast longer. Look back and see we didn't talk about this earlier.

your gain-master works eddie why would isolating not work on the astroplane ?

Bob, everything I'm seeing with my Eznec models tells me that your mast length is the ideal length. I expect this setup to work. From what I see, isolation provides a reduction in the RF on the mast and that should help, because you are going in the right direction, Testing determines the truth, modeling can only predict what might happen.

i don't recall you saying you could control takeoff angle other than raising the antenna either ,

Thanks, I wasn't sure.

i have no idea if there is any truth in the claim a 10-15 degree downtilt can be had by removing the flare in the legs,
its claimed in the patent and says the downtilt may be of some use,

I saw a bit of that with a free space model I did the other day, and I think I posted it for you to see.

what diameter masts are you using in your models ?

The model has a 1" inch mast, but if I add a feed line I will have to change to the coax diameter to the size of the coax and that should change the match and it might not be for the best. That is a failing in this antenna that uses the mast to work the radials.

I'm going to add a feed line, and a choke if I can figure out the very brief instructions. I think Roy wrote his manual for pros in antennas only.