Any Astro Plane Fans ?

[bob85]

Eddie,

This was my parents place, the wheat field is where i did my two pole and same pole antenna testing

the trees on the left are taller than they where & much of the clutter you see across the fields & the fence to the right was not there back then, it was more open,

if you read Henry's article you will find that it is not 2db increase in raw gain, that would be a crazy claim,

it is increase in signal strength received at 30km distance from the transmitter with RX antenna fixed @10mtrs above ground,
a typical height for cb antennas, the variable is TX antenna height,

antenna gain does not tell the whole story since radio is not like a laser-beam its not even like a diffused flashlight,
you have ground reflections that you can include in models,

you also have all the other clutter in the way that I spoke about before that absorb reflect refract signals that you cannot include in a mode

the received signal is a combination of all these possible signals arriving at different phase angles summing & cancelling each other at the RX antenna,

IMHO that's probably why my real world experience comparing antennas never seems to agree with your models raw gain figures,

bear in mind that if 17ft is resonant in free space with no astroplane attached it will have to be longer when you add the astroplane to the mix in the same way a resonant monopole is detuned when you sweep the sigma4 radials up towards it,

they cause an electrical shortening of the whole shebang,

as always I could be wrong.

 

[Marconi]

if you read Henry's article you will find that it is not 2db increase in raw gain, that would be a crazy claim,

I read his article many times and I never understood it like you just explained it.

I didn't even get a clue what Henry's new output was all about until DB posted some work on a similar idea later. I took Henry's words "signal strength" to mean him talking about a regular db I guess.

it is increase in signal strength received at 30km distance from the transmitter with RX antenna fixed @10mtrs above ground,
a typical height for cb antennas, the variable is TX antenna height,

I think that is sort of how DB describe the feature, but his example showed a different term for measuring the results. I asked DB how that value compared to the db or dbi we usually see in antenna models. I don't recall his reply.

So, you believe Henry's new tool explains how and why your Vector Hybrid performed as you've reported back in your youth. Do you think that might also help explain why I got such good results using my Starduster with an 8' foot tubular balun up 54' feet to the hub?

bear in mind that if 17ft is resonant in free space with no astroplane attached it will have to be longer when you add the astroplane to the mix in the same way a resonant monopole is detuned when you sweep the sigma4 radials up towards it,
they cause an electrical shortening of the whole shebang,

I wasn't making a new theory Bob, I was just contemplating that a little over 17' feet on the mast inside the A/P might be getting very close the sweet spot and maybe that had something to do with resonance and the maximum gain and currents you noted. I just divided 206.867" / 12 = 17.2' feet.

I have reached the length of 213.867" / 12 = 17.8' feet using a mast diameter of 1.66" inches. This produces 2.33 dbi gain at 15* degrees, a perfect Average Gain of 1.000 = 0.00 db, and the highest currents on the radiator of all I've compared in this series of models. The model will show all these values.

I haven't checked the currents on the mast yet, but I will. I will post the model later, my computer is doing an update.

 

[Marconi]

Here is the model with the maximum gain, and currents for the radiator only. I will do the currents on the mast later.

The Average Gain is 1.000 = 0.00 db. The match is very good at 27.400 MHz where I see resonance at the feed point.

 

[bob85]

Eddie
I set my mast above the isolator @ 18ft the other evening, the choke is only there because i can't find my ferrite beads at the moment,
i don't think im far from where i want to be but theres always room for improvement even though i won't see it on air,
it remains to be seen if mast current dips when upper 1/4wave current peaks as i think it should,


There's a logical answer to all of this stuff Eddie,

I think you got good results with the starduster because it acts like an efficient 1/2wave with no out of phase radiation when correctly isolated,
I think it probably will at least equal any 5/8 at the same tip height as you have told us all along,

most people including myself in the past don't install antennas correctly & live in a world of CMC where its not wanted,
they bolt them to conductive masts, run ground wires, use no choke or balun, or do use a choke but don't isolate the mast, or do use a choke and isolate but don't use radials so the choke won't work,

after fixing several locals issues with a99 imax & silver rods and seen with my own eyes signal improve, noise reduce, rfi dissapear, i don't do things like that anymore,

I have thought long and hard for an answer to why I got the results I did with the modified vector,
all I can come up with at the moment is surroundings and not having the antenna high above ground, I found a sweet spot that suited my particular set of circumstances as did friends i had tweak their antennas,

yes we all could manipulate signals as I claimed, I was probably off base as to why that was but we live and learn Eddie,

I also got good results here in my youth even when the antennas were anything up to 2 wavelengths to feedpoint but I can't remember how good compared to other antennas & I did not give the shorter antennas a fighting chance by sticking them at the same tip height nor did I properly isolate them,

Henry is a smart cookie, as honest and genuine as they come, a VERY unusual guy for a cb antenna builder,
he taught me a few things I probably would never have learned from other sources,

I have known for many years that radio is not a laser-beam and that reflections play a role even when they bounce off airplanes,
I never saw the results of direct wave + ground reflections combined at the receiver before but that's what happens in the real world,
i just never gave it that much thought before Henry showed me the graph.

 

[Riverman]

. . .most people including myself in the past don't install antennas correctly & live in a world of CMC where its not wanted, they bolt them to conductive masts, run ground wires, use no choke or balun, or do use a choke but don't isolate the mast, or do use a choke and isolate but don't use radials so the choke won't work.

Guilty as charged. Back in the day, I simply attached my A/P to a Radio Shack telescoping mast and began using it with zero thought given to isolation, grounding, CMC, or anything else other than SWR. It worked beautifully, but am wondering what performance would have been if I'd done everything right.

 

[Marconi]

Bob, the currents on the mast for the Free Space model shows to be as you claim.

The highest gain model shows the highest current on the radiator and the lowest currents on the mast. I stopped when I saw the Average Gain result go up.

 

[bob85]

Thank you Eddie,

i know its only a small undetectable increase but id rather have as much of my current in the antenna as possible and as little as possible on my mast & coax,

i was told tales that astroplanes are rfi monsters, i don't agree, no antenna is an rfi monster if its errected correctly to minimise such issues,

DB tells us currents on the mast are always low with this antenna so you would not expect to see much change in current or gain,

i can now be sure my 1/2wave mast & coax isolation is not doing anything detrimental to vswr or gain,

it miminises the potential for noise pick up on the lower mast that is closer to noise sources, it also minimises potential RFI issues .

 

[Marconi]

Bob, I'm using my Free Space model to make a model over real Earth.

I don't expect to see the trends in the currents change much, but it might show us more of a difference in other effects and for sure the patterns will be different.

Since the FS model shows good match with a perfect Average Gain result I'm confident that the model is close. So far the real Earth model didn't crash when I set it over real Earth.

I plan to make the model with and without isolation (ISO). I will also attempt to model a choke on the model without ISO, and see what that might suggest. Again, if the model does not crash, at some point I will make a comparison check of the currents on the radiator and both mast in the case with the ISO model.

To be fair I think I should also make an ISO model with a choke and see if that makes a difference too.

We see Riverman71 indicating his installation was typical and he said it worked great. I have to admit I had similar results back in the day, but back then I knew little to nothing about radiation on the mast, common mode currents, and the effects.

I did later on post that my New Top One was producing heavy TVI, but right now it is on the same mount and at the same height 32' feet...and I don't see the bad effects any more. I can't explain that either, but at that time I had some extra coax on the ground. Later I coiled the extra coax up and hung it to the side of the pushup pole...and the problem stopped.

I expect we will see some differences in the model over real Earth. If my choke idea works...it might give us some more ideas what might be expected with the A/P design.

 

[bob85]

I did not isolate my antennas back then either Eddie,

i did use a choke and isolate the antenna sometimes but not at the same time & not the right size choke,
never gave endfed antennas somewhere for cmc to flow where it won't cause mischief,

how do i know i had it wrong? my vswr would change with coax length,
i knew about velocity factor 1/2waves & 1/4waves as a kid thanks to my mentor Earnie Ashby G3VDR RIP,

i would trim my coax thinking i was finding a node making the coax a multiple of 1/2waves,

i did not understand that what i was actually doing i was changing the electrical length & common mode impedance of the outside surface of the coax braid seen in parallel with the load,
I do now thanks to Walt Maxwell W2DU RIP.


im interested in seeing what your model with ground tells us.

 

[Marconi]

Here are two models that simulate a ground mounted A/P, no isolation (ISO), with and without a choke.

1. model without a coaxial choke and no ISO.

2. model with a simulated choke at the end of the mast inside the antenna at 213.867" inches in overall length and connected to a supporting lower mast to Earth. No ISO.

Notice the differences in red line spacing for the Antenna View images that indicates current magnitudes at these top shortened radiators. The spacing for these red lines from the element gives us an idea for the difference in current (Amp) values noted in the Tabular Currents Log also included. The Manual tells us that these current red lines are not to scale, but again their spacing does suggest magnitude...by their distance to the element. This is similar in a way to 4Nec2 using colors for currents.

Also notice that this difference, in the red line currents, suggest a noticeable differences in balance between the top and bottom of these two antenna radiators...a sure indicator of possible CMC's issues.

Also take notice of the red lines on the antenna masts...another indicator about currents.

Sorry you guys might have to use the PDF zoom feature, a click at the top of the page to see details better.

 

[bob85]

Eddie,

i installed a better viewer so i can zoom,

without the isolation the mast is stealing current from the upper 1/4wave lowering low angle gain, not by much but its there,

its also increasing the likelyhood of local noise from stuff like phone chargers / switching wall warts getting into the receiver & rfi getting into yours/neighburs electrical equipment,

i realise DB showed us low angle gain & vswr been higher with a longer mast but isolating that far below the antenna to test the idea would put too much load on my fiberglass isolator in high wind.

 

[Marconi]

i installed a better viewer so i can zoom,

The images for the antenna and the currents log are both done using a Microsoft snipping tool before it is scanned into the PDF file, so the quality is limited, and you were right the Eznec stuff I've posted is a bit fuzzy. That might be due to technical reasons on my end to spare ink.

without the isolation the mast is stealing current from the upper 1/4wave lowering low angle gain, not by much but its there,

Yes Bob, again you're currents ideas look correct according to my model.

i realise DB showed us low angle gain & vswr been higher with a longer mast but isolating that far below the antenna to test the idea would put too much load on my fiberglass isolator in high wind.

Bob, my model still produces a pretty good match and gain using a 200" inch mast, but going to 214" inches shows the best results. I used a 5" insulator for this model, but it also works with a 1" inch insulator.

All that is left now is;

1. a model that is insulated (ISO) using a choke vs. without a choke.

2. a model without a mast and with coax fed 90* degrees to the vertical.

Bob or anybody, have you ever heard tell of making the AstroBeam horizontal? If so, what do you think was done with the mast in that case?

 

[bob85]

I have only seen what the patent says, that the astroplane could be used horizontal,

I think that's probably just to stop other people taking the idea and laying it down to circumvent the patent,

I can't imagine an astrobeam clamped to a mast @ 90degrees
especially if it still needs some space between the hoop and the vertical mast, it would be a mechanical nightmare,

two astrobeams on a common horizontal mast to balance the weight about the rotator maybe,

very expensive way of getting gain IF it works.

 

[Riverman]

I can't imagine an astrobeam clamped to a mast @ 90degrees
especially if it still needs some space between the hoop and the vertical mast, it would be a mechanical nightmare.

Bob, back in the 70s I used to talk to a fella about 30 miles away. One day I noticed his signal had dropped a few S Units and he wasn't as loud. I asked if he was having a problem and he laughed and said, "No problem here. I'm running my Astro Beam flat these days." Said he did it to better talk to a friend of his fifty or so miles to his south who was using a horizontal beam. Also said it was better for talking skip.

Am pretty sure he gave no thought to all the things you guys have been discussing.
I don't even think he had a rotor. Rather, just turned the mast by hand.

 

[Marconi]

Riverman, I think maybe your friend might have done just what you said and spun his beam around to horizontal, but it wasn't an original AstroBeam.

The original A/B construction will not allow spinning around the boom like some other beam antennas will do.

Edit: the supporting mast is inside the hoop of the A/P driven element and the boom is pinned in place inside the mounting hub.