ASTROPLANE best vertical antenna ever?

[Slowmover]

A studio has been rented, script is writing itself, as,
The Bob & Eddie Podcast
is coming together.

“Folks, please hold off on those phone calls . . Quarter-Wave Isolation will be addressed!”

(No snark. I’m enjoying hell out of this thread).

.

 

[bob85]

Eddie & DB

I want to thank you both for your input on the astroplane, for bearing with me waffling on about current modes you can't see in your models & providing me with models I can't make to test my ideas,

I don't know about you guys you may not be convinced,
but I am satisfied that between us we worked out what's going on with the astroplane,

I am 99% sure its a form of inverted open sleeve antenna,

it is not a 1/4wave groundplane as some claim

show me a groundplane antenna that when you adjust the mast from 1/2wave to 3/4wave feed-point impedance goes significantly up ,

show me an antenna with 1/4wave looking current distribution on a 1/2wave conductor

nor is not a 5/8wave I won't even go there its silly,

what it is an efficient halfwave aperture inverted sleeve monopole, with about the same gain as a dipole,

don't believe me go model a resonant open sleeve antenna with a good match to 50ohms that has a 1/2wave monopole & 1/4wave sleeve,
where the transmission-lines are looking at the low end impedance of a 1/4wave & look at the current distribution,
does that not look odd? like a 1/4wave distribution on a 1/2wave conductor ?

Then extend the monopole to resonant 3/4wave where mast antenna mode impedance goes down at the feed-point while the opposite end of the lines are now looking at the high end impedance of a 1/2wave,

feedpoint impedance goes up like nothing you ever saw before when adjusting the length of a conductor from 1/2wave electrical to 3/4wave electrical,

you won't find that happening in any groundplane or 5/8wave,
it only occurs in antennas that have transmission-lines within their construction,

there are two currents in superposition IT & IA with IT been the dominant current mode causing radiation from the sleeve due to common mode current as seen in open sleeve antennas using a resonant 1/2wave mast & resonant 1/4wave sleeve,

what do I mean by two currents in superposition?

Whenever you have two sources of excitation in different positions in a circuit carrying currents you have two currents flowing that are is superposition, one is superimposed upon the other, IT & IA are in superposition in the astroplane,

two currents two modes in the antenna, CO ( together or jointly ) -INDUCTIVE ( been induced )

does it matter that it only has about the same gain as a dipole ? NOT AT ALL,
why because the competing antennas don't have the claimed gain either,

it has been known for a long time that an efficient halfwave mounted at the same tip height as a 5/8wave actually has a little more low angle gain than a 5/8wave,

that is because all currents on a 1/2wave are in phase whereas a 5/8wave has 1/8wave of deconstructive radiation in the lower 1/8wave that detracts from its extra height of current maxima where it actually gets its extra claimed gain from,

so you don't get the full benefit of the extra height like you do by installing a 1/2wave at the same tip height,

the astroplane takes that a step further, shortening the upper monopole with the hat does two things,

it reduces vswr bandwidth & raises current maxima higher above ground when installed at the same tip height as competing antennas,

raising current maxima higher above ground than competing antennas mounted at the same tip height is an advantage whenever you are restricted to a maximum antenna height such as your old FCC regulations dictated,

a correctly installed astroplane at the same tip height will give any groundplane out there a hard time,
what do I mean by correctly installed?

Isolate the mast a little over 1/4wave below the hoop,

use a proper choke on the coax at the isolator,

do not run random length ground wires to a ground rod as most people do,
it won't help & could mess it up and cause rfi & more noise in rx,

if you want to ground it buy one of those coax clamps & ground the coax to a ground rod.

 

[Marconi]

I want to thank you both for your input on the astroplane, for bearing with me waffling on about current modes you can't see in your models & providing me with models I can't make to test my ideas,

Bob, I don't think you were waffling. Maybe it was an issue in explaining what you were seeing in you minds-eye and thinking. I'm not sure what DB understands, but tor me it is nothing compared to my lack of understanding of those ideas. I think maybe a lot of genius ideas go inexplicable...at least in my world.

feedpoint impedance goes up like nothing you ever saw before when adjusting the length of a conductor from 1/2wave electrical to 3/4wave electrical,

you won't find that happening in any groundplane or 5/8wave,
it only occurs in antennas that have transmission-lines within their construction,

I saw the impedance go crazy when I followed your instructions and set the mast near resonance as a 3/4 wave. That gave me the information to see what you were describing in words. Now I understand a bit more of what you've been saying...when you talked about transmission model current effects.

two currents two modes in the antenna, CO ( together or jointly ) -INDUCTIVE ( been induced )

I think for a long time I've considered the guys at Avanti to be very smart. I guess they knew exactly what to expect from their customers...if they got too technical in explaining what Co-Inductive really meant. Thanks to you Bob, you figured it out though.

does it matter that it only has about the same gain as a dipole ? NOT AT ALL, why because the competing antennas don't have the claimed gain either,

Bob, this is why I recently made my posted #360 at this link. ASTROPLANE best vertical antenna ever?

I had an idea to try and shed some light on how some antenna makers were reporting very high gains for their antennas, gains that are likely way to high to be accurate.

I was able to produce a model of the Avanti Astro Plane over Real Earth that showed the high gain that was similar to what Avanti had advertised for years...near 4.50 dbi gain at a low angle. Everybody liked to see an A/P that was right up there with the best of the modern day high gain antennas, but IMO that gain was likely overstated, due to a hign AG test result, which was likely never considered with those overstated gain models we often saw in magazine ads.

So, I followed this model up with what I thought was a more realistic gain results. All I did is build my model while checking the Average Gain results and making sure it was = 1, as I updated my model. As a result, this model showed a more realistic gain, and on posting this new model, I'm sure some folks would be saying, "BS."

a correctly installed astroplane at the same tip height will give any groundplane out there a hard time,
what do I mean by correctly installed?

Isolate the mast a little over 1/4wave below the hoop,

use a proper choke on the coax at the isolator,

do not run random length ground wires to a ground rod as most people do,
it won't help & could mess it up and cause rfi & more noise in rx,

if you want to ground it buy one of those coax clamps & ground the coax to a ground rod.

Sounds like a good plan to me Bob.

With my recent sense of appreciating a vertical monopole, where the antenna works generally with a much lower "noise floor," (an S-Meter reading when no RF signals are to be noted on the meter)...I think much of what you are describing above will surely help your RX receive pleasure in operations of you station.

Bob, did you make your A/P with a full 1/4 wave radiator?

 

[bob85]

Eddie,
I was waffling on about currents you can't see for many years just like I did in the sigma4 thread, they are there you just can't see them,

that's why I got it into my head at one time that NEC was not painting a true picture of the sigma4,

I thought if its not using the real transmission-line function or you are not adding the extra wire to simulate the outside of the braid or sleeve you won't see the radiation,

Cebik squared that up in my head,

if a j-pole in NEC shows the radiation from the short leg due to unbalance at the top of the stub,
it must follow that its showing you radiation in similar antennas due to the same currents such as
open sleeve antennas sigma4's & THE ASTROPLANE.

No Eddie,
I did not remove the hat & extend the upper monopole to restore resonance, I had a play on the plastic drum but not up in the air installed correctly,

if you do that then the rules on hats are,
besides changing current distribution they reduce vswr bandwidth, I think that's what the patent claims also,

you lose the astroplanes advantage in height of current maxima when installed at the same tip height, but that does not matter if height is not a restriction,

I used to think Lou & Herb were smart guys, then I changed my mind & thought like you its mostly marketing BS,
that was my lack of understanding not theirs,

over the years I have come to respect those guys even more than I ever did,

DO I think Lou & Herb knew a thing or two about antennas,

OH YES they sure did,
there is zero doubt in my mind that they understood more than your average bear about antennas,
you don't come up with the astroplane design by accident,

its not like they just accidentally bent a starduster in the trunk lid & found they had low vswr,

the un noticed things like flaring the cone to maximise unbalance while keeping ZT in the ballpark,
that's no accident that's somebody that understands transmission-line theory,

there are some pretty sharp folk that still think the astroplane is nothing more than a 1/4wave groundplane,

a few simple tests as you have done with mast length would demonstrate that is FAR from the truth,

you won't convince DB its just a 1/4wave groundplane either because he's seen effects that just don't happen in any groundplane.

To people that never did any tests or models its easy enough to see just a 1/4wave groundplane.

NO Eddie, we figured it out, joint effort,
without you & DB making the models & noting effects i propbably would never have zoned in to what was going on & gone looking for things that could explain it.

 

[bob85]

DB said,

"I think there is more going on with this antenna than many (in fact most) people realize"

Eddie,
The smartest antenna guy I ever corresponded with told me the same thing years ago,

I hope after 7+ years 424 posts & near 71,000 views that a few more people do understand that there's more going on with this type of antenna than is apparent to most people,

I can't go back and edit my post so i will add my point here,

i would like anybody to show me any groundplane antenna that when you extend the isolated mast from 1/2wave electrical to 3/4wave electrical,

you see feed-point impedance go up into the hundreds of ohms while simultaneously current in that 3/4wave also goes up significantly.,

That alone should prove the astroplane is not just a fancy looking 1/4wave ground-plane.

 

[Marconi]

Bob, now I see a little of what you've been talking about for a long time.

I wish I had the complete idea in my minds-eye like you do.

Thanks for your patience over all the years.

 

[bob85]

I wish i had the complete picture in my minds eye too Eddie,

next time i put my astroplane up i want the mast & the choke as close to 1/2wave as i can make it,

last time i guessed the mast was 1/2wave above the isolator,

next time i will try to tune the mast & coax for least reactance at the feed-point ,

i will have to rewind my choke every time i adjust the mast but that kind of experimenting interests me.
then i will extend the mast to 3/4wave to see what happens with current on the coax braid,

does it go up or does it just screw the vswr up.

Thanks Eddie

 

[Marconi]

then i will extend the mast to 3/4wave to see what happens with current on the coax braid,

does it go up or does it just screw the vswr up.

Thanks Eddie

Sorry for the big print Bob, it helps me with my bad eyesight.

When I read your comment above, I said to myself, base on what I reported the other day...when I said I made the mast inside the loop as close to a resonant 3/4 wavelength as I could...and then reported that the match went crazy and so did the SWR, I had a couple of thoughts.

1. why would Bob want to go to the trouble for that idea considering the trouble making a choke for each iteration in his testing.

You don't have to answer Bob, I would do the same, just to be sure, if I could.

2. since I discarded that model with a 3/4 wave mast I was referring to...maybe I should check that again and maybe the model might give him an idea for how long the mast might be when it is resonant.

3. maybe I should check what I did earlier on Bob's 3/4 idea.

So, I'm doing this 3/4 idea over again and on first go around...it looks like I was wrong earlier. Now I see the currents blooming-up on this mast and that is not different, but the match and the SWR seem, so far, to be only mildly ill-effected.

That said, I have not gone back and fully checked everything yet.

To continue. when I tweaked this length it came out to be 340" inches from the 325" inches I stated with. This initial 325" length was base on the Eznec calculation for a full wavelength at 27.205 MHz. Now the reactance is showing, X = + 0.2565 ohms. So 340" could be close for a start.

Now the models pattern is different, but not too bad, and it shows only 1 lobe with a maximum gain at a low angle. The SWR match is still decent and the model is resonant at the 27.205 MHz right where the model is set. I've done nothing to the model to mitigate CMC's, except the insulator between the antenna mast and the short supporting mast.

So, the model does not look as bad as I claimed before. Bob, I could have just goofed up and overlooked some setting...who knows. I did not save that model, and that was..............Stupid of me.

I hope to get back at this tomorrow.

 

[bob85]

Now we have a problem Eddie,
not for me because i use 1/2wave mast but for knowing what length to avoid,

you have not grounded the mast have you ?

DB noted as you did the first time impedance going way up around 3/4wave,

what is different in this revised model vs the first one ?

if its just the mast that is a little longer, then the length that screws it up is what to avoid,

this is what i would test if the astroplane was up, whats going on with current below the hoop when the mast is 3/4wave resonant & whats going on with current when vswr goes crazy

i would also check current is minimum when reactance at the feed-point is lowest with the 1/2wave mast
i would have to redo my little current meter to fit over fatter coax or change coax,

rewinding the choke is easy, few minute job,
its 5 turns wrapped around foam former on the fiberglass isolator, if i extend the mast the coax won't reach the antenna connector,

thanks Eddie.

 

[Marconi]

Bob your 3/4 test is just like you have described it in the past...the A/P is up side down.

 

[bob85]

Now its starting to look similar to a 3/4wave sleeve monopole on a 1/4wave mast turned upside down Eddie,

the mast looks longer than 3/4wave electrical,
maybe some reactance in the mast is cancelling reactance in the sleeve area to give a net x= 0.2ohms at the feed-point, its something to look into,


even if the pattern is not so bad i don't want my mast and or coax radiating and receiving anything if i can avoid it,

if that antenna was just ouside your shack window it would be more likely to cause rfi and receive noise from electrical equipment, than the 1/2wave mast version at the same height,

Thanks for the model

 

[Marconi]

When I did your 3/4 mast test on my Bob's A/P model, I saw the current on the A/P shortened radiator, drop like a rock.

So the mast, in this case, appears to have stolen currents from the A/P radiator, thus making the model appear to me...needing to be upside down. That is why I turned my model up side down and posted the results.

It now looks surprisingly like a S4/NV4K...just like you've been telling us. I for one never quite grasped that description until now. Thanks!

Bob you mentioned, in your real test to find a resonant 3/4 wavelength mast, that you would have to redo your choke with each iteration in the process of testing for resonance. I don't have a choke and I don't have a Feed Line on my model.

But if I did? Where would I place the choke in this case?

 

[AudioShockwav]

A light bulb just went on over my head.
Thank you guys for going down this road, that model of the upside down antenna paints a picture that I never could see properly in my mind.
All I can say right now is wow.

73
Jeff

 

[bob85]

Right where you have the isolator in that model Eddie at the end of the mast same place i have my choke with my 1/2wave mast,

i used 2 feet of thick wall fiberglass tube with scaffold pole clamps at either end.

Have you seen a 1/4wave groundplane where adjusting the mast from 1/2wave to about 3/4wave robs current from the radiator like that before Eddie ?

 

[Marconi]

A light bulb just went on over my head.
Thank you guys for going down this road, that model of the upside down antenna paints a picture that I never could see properly in my mind.
All I can say right now is wow.

73
Jeff

Jeff, until recently, I too was not able to visualize Bob's description in this case.

Like I've said before: "..,when I learn something new of a day...I consider it a GOOD day."