ASTROPLANE best vertical antenna ever?

[bob85]

Not much difference there Eddie, it can't be the segments & junctions causing the poor mach,
you must be right its how you do the feed-point,

Here's something to think about,

If a coax dipole like a gain-master is a center fed antenna because you attach the coax to the so239 & the signal travels up an unbalanced 1/4wave transmission-line to the center of the antenna before it starts radiating from the outside of the unbalanced line & upper 1/4wave

what do you call an antenna where you attach the coax to the so239 & the signal that causes most of the radiation travels down an unbalanced transmission-line to the hoop before causing radiation on the outside of the unbalanced line via common mode,

is the hoop really the lower end when the 1/2wave mast is an active part of the antenna.

The astroplane should have been called Avanti conundrum,

its an effective 1/2wave radiator,

its 5/8wave physical height with the hat or 3/4wave with the full size upper 1/4wave,

if you remove the mast it acts similar to a center fed dipole

when you add the 1/2wave mast it acts like an inverted open sleeve antenna mostly voltage fed at the hoop,

when you extend the mast it starts acting somewhere between the two,

it is a conundrum of an antenna but they work great when installed correctly.

 

[Alexis Mercado]

What if you have it 36 feet high ?

 

[bob85]

That's about where mine was but it was isolated 1/4wave below the hoop,
vswr readings were almost identical to your Alexis.

 

[Marconi]

What if you have it 36 feet high ?

Alexis, I will be making a model at 36' feet when I am more clear minded.

I had a bad day yesterday. I wanted to try the dimensions that Alexis posted, but I couldn't concentrate.

Later, I found Alexis's dimensions to be a bit longer...at least that is what the model showed. Bob, I thought Déjà vu, the model was back, again, looking similar to before.

So, I was trying to figure out, again, what was going on.

I did discover there is nothing wrong with DB's method or his location for the A/P feed point.

Basically, I now see both methods working almost exactly the same in Free Space so far.

The big difference is DB reports that his model was limited to a 1" antenna mast. I saw the same in my older models of the A/P too.

In trying to make a model using Alexis's dimensions that were a bit inductive, again I managed to make an A/P that worked and allowed me to do it with a 1.50" mast, that is one inside the radials and extending below the hoop.

Hey guys, I don't have these problems with my Old Top One model. That said, until recently I seldom if ever posted a OTO model. I called it an A/P.

REASON, I figured nobody would know what an Old Top One antenna is.

Now when I open an older A/P model, I have to first try and figure out if it had OTO dimensions or the A/P dimensions.

So, when I see this difference it means something to me...that is why I've been cranky in asking for good accurate or better dimensions. I didn't mean to be so snarky.

 

[Marconi]

That's about where mine was but it was isolated 1/4wave below the hoop, vswr readings were almost identical to your Alexis.

Bob, did you take your A/P down? If so. can you tell us why?

I think I also asked Alexis somewhere, why he was taking his A/P down, but

 

[bob85]

Yes i took it down to put the Gain-master up Eddie, i wanted to put my antenna higher,

the astroplane on its 1/2wave mast & isolator has a much higher wind load than any other vertical i own,
its also MUCH heavier to walk up and down on your own when you put a 1 wavelength pole under the isolator

and its tuned for your band not ours, no good for 10mtrs without a tuner for me,

Gain-master works OK without a tuner from below CB band up to 29mhz,
its easy enough to walk up & down on a 1 wavelength pole without any help,

& i don't care if i drop the Gain-master or the wind destroys it.

 

[Marconi]

Sounds like a good idea to me, I was just surprised.

I loved my Gain Master, but a lightening strike nearby in the neighborhood popped the center section near the stub. It was not a direct hit or FG would still be flying around and in the yard.

I walked my stuff up until about 5 hears ago went I got a pacemaker for my heart.

I used a push-up-pole and walked it up. Then I got on a ladder and raised that bugger up as far as it would go. I even added a 10" x 1" heavy wall tube bolted to the top of my PU Pole. I could still handle that with some of the lighter antennas. That extended the 40' foot PU to <50' feet.

Could you tell a difference in the noise between those two?

 

[HomerBB]

When I had an old original Astroplane I found it to be extremely light.
According to online sources the Astroplane weighs 4lbs, while the Gainmaster weighs 5.7lbs.
I also never found it to have much wind load, in fact, very little compared to a 5/8 GP with 4 x .25^ radials. One of the advantages I've expressed about it more than once is how light and extremely easy it was to mount up high.
Curious that Bob has the opposite experience with weight and wind load. . .
@bob85 , you're not supposed to hang boat anchors on them .

 

[bob85]

Homer

its a simple surface area & newtons law of moments deal,
the astroplane specs are just the bit that comes in the box,
when you add the needed 1.5" mast the wind load & weight is significantly higher than any contemporary groundplane,

plus i have the isolator and a fatter pipe above the isolator that the 1.5" pipe telescopes into,
If i used a 1/2wave 1.5" mast it would break in wind unless it was very thick walled heavy & expensive to buy and transport.

Eddie,
i see no notable difference in noise between Gain-master & Astroplane,

i find most peoples noise here comes from electrical goods in close proximity to their antenna & unchoked coax, conductive masts & willy nilly ground wires,

a noisy antenna is a poorly isolated antenna in my experience.

 

[HomerBB]

Thanks, Bob, for the explanation.

 

[Alexis Mercado]

That's about where mine was but it was isolated 1/4wave below the hoop,
vswr readings were almost identical to your Alexis.

What is the purpose of using a line isolator ( not the ugly one) on these antennas ?

 

[Marconi]

Alexis, I will be making a model at 36' feet when I am more clear minded.

Alexis here is the model at 36' over real Earth ground using your dimensions. Thank you.

I also took this model and shortened the Top Hat radials in 4 iterations @ 1" inch each. Here I posted the Recap Report showing the lowest SWR at the center frequency...due to each change noted for wire #5 in the model. I did not keep these models, so I won't be able to discuss the details.

I did not try and tune any of these models either, and the match got worse and worse as one might expect on shortening these radials.

You might try the idea you talked to me about, but I have no idea how of if you can fix the matching.

I still consider this antenna to be a center fed vertical Half Wave dipole of sorts, but all the wire interactions are very complex, just like Bob has been describing in this thread.

I also made the Top Hat radials 9.5" inches long, just like you suggested, when saying you were going to use the radials off you SP 500 antenna.

The match got really bad and the frequency went up to 29.605 MHz...those SP 500 radials are way too short in this case.

 

[Marconi]

What is the purpose of using a line isolator ( not the ugly one) on these antennas ?

Here I used your model I just posted above. I simulated the mast without anything to mitigate Common Mode Currents on the mast and feed line. Among other things, the pattern went bad as you can see.

Check close and you'll see the titles are the same.

There is a lot more to this issue. This antenna needs to be fixed for the problem, and Bob has told us what he did, somewhere above if I remember correctly.

 

[bob85]

Alexis,

the isolator I use is to isolate the mast about 1/4wave below the hoop to minimize current in the mast below the hoop as seen in the two models with & without the isolator that Eddie posted above,

you also need to isolate the coax at the same place below the hoop with a good choke for 27mhz, not the "ugly balun" on ham universe,

some mast or coax lengths will make the Astroplane act like an upside down j-pole or open sleeve antenna with high levels of radiation from the mast or coax.

That can cause RFI in the shack and noise from electrical goods to be received on the mast and coax.

I never want my mast & coax radiating even if the model shows more gain,

that gain won't be useful if your ears are plugged with noise & you are causing rfi in the shack.

 

[Marconi]

Here is a video that I think discusses this issue in simple terms.