ASTROPLANE best vertical antenna ever?

Alexis, there is a member here on the forum that has one, and it has not been installed yet.

If you ask him, maybe he can get you some measurements.

Eddie,

I had the 1/2wave mast idea because a 1/2wave gives the highest end impedance & lowest antenna mode current in the mast & highest unbalance situation at the end of the transmission-lines,

look at a j-pole with only 1/4wave radiator above the stub vs 1/2wave above the stub

DB said he found a little longer than 1/2wave was optimum to the best of my recollection,

I don't see a problem with that because when you put a radial sleeve around a mast,
or the cone around the sigma,
or anything similar open sleeve skeleton sleeve etc it forms a transmission-line or lines,

you introduce an impedance seen in parallel with the radiators antenna mode impedance & transmission-line mode currents flow,
the conductors proximity causes all conductors involved to be electrically shortened,

as you bring the conductors closer, transmission-line mode impedance decreases, transmission-line mode current increases & resonance shifts up in frequency,

so the astroplane mast will be electrically shortened to some degree meaning it must be lengthened to restore resonance,

was DB's mast when adjusted for best low angle gain acting as an electrical 1/2wave because the astroplane makes it electrically shorter than its freespace electrical length ?,

That would be my guess, I could be wrong, I am sketchy on exactly what length & diameter mast DB said was best,
isolated about 1/4wave below the hoop works great for me,

The sirio is a different antenna entirely but imho will perform about equal to the astroplane with better symmetry,
if I was installing a sirio top-one it would be isolated a little below the radial tips the same way I would install a starduster.

Eddie, what do you see down that rabbit hole,

Marconi said:

The gain did drop a little compared to the longer antenna mast that DB and I have been using with the A/P design. I was thinking that making the antenna mast longer, closer to a 1/2 wavelength was your idea.

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Marconi said:

If DB didn't come up with that idea, then it had to be GHZ24. But with that said, back in the days I tried to add his 4NEC2 details into Eznec and the model didn't work good, and I didn't see him using a long mast element inside the radial cone either. He did say his model was only close on specs however and I never went back and checked.

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bob85 said:

DB said he found a little longer than 1/2wave was optimum to the best of my recollection,

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I'm not sure if Bob85 came up with it as well, but when I said it it was based on results from modeling. My first attempts at modeling the Astroplane was not to spec, but my later models were made to spec, and those worked the same. It was longer than 1/2 wavelength in physical length, but as I recall not much. That is where the antenna to tuned to resonance.

bob85 said:

I had the 1/2wave mast idea because a 1/2wave gives the highest end impedance & lowest antenna mode current in the mast & highest unbalance situation at the end of the transmission-lines,

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bob85 said:

so the astroplane mast will be electrically shortened to some degree meaning it must be lengthened to restore resonance,

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The thing about the Astroplane antenna and a 1/2 physical wavelength mast, the current distribution was strange. On my little longer than 1/2 wavelength mast I had an electrical 1/4 wavelength current distribution. I have never seen that before, and I haven't seen in on any antenna I have made since, however, I have modeled the Astroplane several times and every time the physical 1/2 wavelength mast had the same current distribution. At the time I attributed it to the basket of the antenna and its proximity to the mast within, but I was surprised that there was that much of an effect.

I have my own thoughts on what is causing this, but that goes beyond what is being discussed currently, so far so I won't go into it.

bob85 said:

was DB's mast when adjusted for best low angle gain acting as an electrical 1/2wave because the astroplane makes it electrically shorter than its freespace electrical length ?,

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bob85 said:

That would be my guess, I could be wrong, I am sketchy on exactly what length & diameter mast DB said was best,
isolated about 1/4wave below the hoop works great for me,

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If you are talking about gain on a model with an earth, changing the mast length won't change that angle. As I recall it did have an effect on the angle in free space, but it wasn't much.

At least one of the masts was a 1 inch diameter, stainless steel mast. Another was 1 inch diameter and aluminum. I was limited to 1 inch in diameter because of software limitations and this model design. I could have use a smaller diameter section then transitioned to a larger diameter, but the modeling software doesn't even handle that very well so I didn't bother. I would be surprised if a 2 inch diameter mast would have made more than an inch of difference in length.

Actually, due to this antenna design, the antenna itself is very forgiving when it comes to mast length. At odd 1/4th wavelength multiples there are areas that you will have trouble tuning this antenna, according to the models that was an area less than a foot in length (as I remember) before it was good again. In this limited range of mast length it wasn't only tuning that was bad, but the models showed that the antennas radiation pattern would switch to a higher angle lobe as well. Aside from these small areas, the antenna was remarkably stable both when it comes to tuning for a low SWR, and performance. Sure, there were variations when it came to performance, but it wasn't anything that you would notice...

When it comes to mast length and gain, there was a wire that at the time I called the "blue wire", and if the mast was tuned to resonance, you could remove this wire with very little effect on the antenna. When the wire was gone and the mast was this length is when I saw the highest gain for the mounting location that I used. I discussed this with HomerBB. Unfortunately, with said "blue wire" removed, the antenna was very sensitive to the mast length, and even a small change would drastically affect the antenna's tune and performance.

Hope this helps.


The DB

I want as little current on the mast as possible & i want to receive as little noise as possible on the mast & coax braid DB,

i would be interested in hearing what you think is going on if you ever feel like sharing your thoughts.

I just saw a YouTube video about this Tagra BT-101. It says it is a 5/8 wavelength antenna, measuring 4.42 cm ( 14.5 feet ) with 4.15 dBi, making this Tagra antenna longer by 2.5 feet.

See pics

bob85 said:

I want as little current on the mast as possible & i want to receive as little noise as possible on the mast & coax braid DB,

i would be interested in hearing what you think is going on if you ever feel like sharing your thoughts.

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AudioShockwav said:

I would also be interested in your thoughts on the subject as well.

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When it comes to the mast, the part of the mast that attaches to the feed point of the antenna will always have a high current. If you isolate the mast from the rest of the antenna then you will not be able to tune this antenna. When I would model said antenna without the mast I could never get it to tune, it was like I was trying to tune a 1/2 wavelength loop, the impedance was simply to high. Also, the odd 1/4 wavelength lengths I mentioned above, they have the same effect on the antenna, they resist current flow on the mast, and in doing so the antenna's feed point impedance skyrockets for a few of said mast lengths.

Don't forget the feed line, which is not showing up in our models, but even if the mast is at one of those bad (unlucky?) lengths, if the feed line is not at a bad (unlucky) length then the antenna will use that instead. The odds of both of them being essentially within a bad 1/20 of a wavelength in length is very low, and I haven't heard of anyone who had actually had this type of problem happen to them "IRL". I only know that it is possible because I saw it happen in models when I tested this antenna with a lot of mast lengths.

As for the half wavelength length of mast acting like an electrical 1/4 wavelength conductor, which as I have stated above I have only seen in models of this antenna, for various reasons, I don't think the metal in the basket area will have enough of a capacitive effect on the mast to cause us to need to add that much extra mast to compensate. Because of this I have come up with two lines of thought on this.

1) The basket area is inducing out of phase currents in the mast area that are interacting with the currents already there to create the current distribution shown.

2) The bottom of the basket is a voltage node. As this is near the mast, in fact completely surrounding it, I think this peak voltage area on the antenna may somehow be amplifying the capacitive effect on the nearby mast. I think this is possible mostly because capacitors (and by extension anything that has capacitance) are voltage devices.

It is possible that I could be wrong, the basket area might be able to do this on its own, its just that when working with antenna models, I have not seen this "small" of an amount of metal have that big of an effect on current distribution outside of this antenna.

Alexis Mercado said:

I just saw a YouTube video about this Tagra BT-101. It says it is a 5/8 wavelength antenna, measuring 4.42 cm ( 14.5 feet ) with 4.15 dBi, making this Tagra antenna longer by 2.5 feet.

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There are a lot of people that believe that this is a 5/8 wavelength antenna, and there are just as many that swear that this is nothing more than a 1/4 wavelength antenna with a fancy matching system. I can make very good arguments on this antenna being several different wavelengths, and I have very good arguments against each and every one of said wavelengths. I think the biggest problem here is far to many people get to hung up on the length of the antenna (in wavelengths) and fail to take into account other factors which can be even more important.


The DB

The DB said:

There are a lot of people that believe that this is a 5/8 wavelength antenna, and there are just as many that swear that this is nothing more than a 1/4 wavelength antenna with a fancy matching system.


The DB

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It is the Tagra BT-101 manufacturer who states his antenna is a 5/8 wavelength antenna.

DB
i don't recall the specific model with the odd current distribution, i do recall you mentioning it though,
its clearly not a 5/8wave in the generally accepted form,

i see a 5/8wave elongated loop with relatively high impedance low antenna mode current,
until you add the mast, the impedance drops and you have more current flowing,

where else can current flow if you have not changed the physical length of the loop but current went up significantly ?

i think it is flowing the transmission-lines you just created adding the mast, thats what happens with sleeve antennas j-pole sigma4's etc,

is my transmission-line mode impedance the same thing you are calling capacitance DB ?
the thing that shift resonance up & lowers feedpoint impedance the closer you bring the conductors ?

the 1/2wave mast has high end impedance low current until you add the antenna,

neither the mast nor the antenna carry much current until you combine them into transmission-lines,
Co-Inductive

i would not be surprised if the electrical 1/2wave mast had more current inside the basket than below it,
IF its working like i think it possibly does with significant current flowing in unbalanced radiating 1/4wave flared transmission-lines,

something you did with the blue wire had me baffled but i can't remember what it was exactly.

thanks for sharing your thoughts & the models you have made for us in the past DB.

Alexis,
the extra length of the tagra is including the 2 section support mast,
it is a copy of the astroplane, they won't work on the same frequencies if its not the same size.

Ok. Thanks Bob.

Bob, I just re-modeled my OTO in Free Space and I wanted to track the AG test results for accuracy as I removed the mast inside the cone to see what happens.

I was also curious to see if I could tune such a model.

The match did not look so good after removing the mast from inside the cone, including the mast to ground. I then removed all the standard losses from the model to make a Free Space setup.

Then I asked myself...what simple things would Homer think to do here?

I ran the AG continually as I tuned. The radiator was first and it ended up at 91" inches as it stopped improving the reactance.

The cone was already setup at 87.9" inches.

The resistance was still in the weeds and it didn't look good.

The first try at fixing the resistance was making some adjustments to the spacing at the radial to mast bracket near the middle of the 2 radials. I got those 4 adjustments made and it too was surprisingly close.

I then tweaked the resonance at the radiator tip some more as I watched, and was seeing it change. I tweaked the AG results at wires #2, and #3, the feed point.

I tweaked the overall matching using segment count adjustments and wire diameter adjustments...again at wire #2 and #3.

When I got the model as good as I could, I scanned the match and determined it need a transformer. Add what I thought was needed, I tweaked the value until I got a near perfect match.

I was using Loosecannon's dimensions...which I found earlier to be right on the money in previous models.

Based on how far the match was off on removing the mast...I was really surprised and happy at how small the adjustments needed to be. It seemed like nothing more than fine tuning...similar to what I had done for years on my real antennas.

Maybe this idea is worth a try in the real world...hello Homer. You're the only guy I know that could do this.

The Real Earth model is in the testing stages. Adding back the losses can be more of a surprise than removing them. The basic Real Earth model didn't miss a beat, but I'm trying to add a feed line to be sure. Next I have to try and change the antenna height and see if the model will stand the change without breaking.

Eddie i don't understand removing & adding in the losses in any antenna software,

current distribution in this model looks to my untrained eyes like a regular dipole with the lower legs sharing the current that is flowing into the upper 1/4wave as per kirchhoff's current law,
i don't think that's whats happening when the mast is installed & you have two tapered 1/4wave transmissin-lines but i could be wrong,

I am always willing to learn & change my thinking.

Bob, here is the model in post #372 shown above with a short feed line added to the model. With a good choke on wire #38 I see very little change in the model. I also made the FL = 600" inches but I didn't add coax losses to the model, so no change.

I just wanted to see if I could make this model work with a feed line attached, so we didn't have to muck-up the antenna without a mast and still see is work with the FL in a better location.

I can't claim any of this will work in the Real World, but I can get this idea to tune with a little patients and effort.

Next, I will add the coax losses for 600 feet of RG-213 - 66% VF.

Eddie,
can you look at the current log to see if current going into wire 1 is equal to the sum of the currents in wires 4 & 5

if it is i would say its acting similar to a 2 radial starduster,
not sure how with the hoop at the radial tips but thats what it looks like to my eyes.