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Any Astro Plane Fans ?
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Homer, whats about the isolation of the mast on what the Astroplane is mounted, i have read several times in the net?
Victor
Victor
There seems to be a lot of mystery about this antenna. So, speculation , or guessing things about it, happens. As with all antennas people give attributes to them that are not necessarily true. Because the antenna uses the mast as a part of the antenna some assume it needs to be isolated at a certain point blow the ring, or if someone has experienced common mode currents resulting in TVI they may believe it is due to not having the mast isolated because of what someone wrote in the internet. The story gets bigger and bigger with time.
DB has been modeling some of those ideas in this thread about mast lengths and such, and he may remember more correctly, but nothing has proven the need for isolating the mast from earth. Only that the mast contributes to the overall function of the antenna.
I have had the AP, both a homebrew and a factory model, up several times on masts of different lengths. Once I had it up 10' above a 4 element Yagi. In none of those installations from ~6m to ~12m to the ring did I ever experience any odd behaviors from the antenna to indicate the need for isolation along the mast anywhere.
Install yours and enjoy it.
No Tib.
I was close with my previous model of the orignal Avanti A/P using dimensions from others and my trying to use the manual, but the model was not looking good without changing some specs...which I did not want to do.
Your dimensions give me the exposed dimensions and IMO that is what I need for a reasonably accurate model.
You show a nice image of the hub with tape measure and indicating most of the dimensions, but I don't see the dimension for the distance between the center of each radial. Just to be sure, would you remeasure your mounting hub from center to center for the two down elements? I get 6" inches and you get a fraction more.
That said, I can't be sure a fix to this model using new dimensions will change the performance, but we'll see.
I have not fixed my model using your numbers yet. I'm just not up to concentrating on all the details.
If you can and just for the record, when you get your antenna built, please double check and see if all of your exposed tubing dimensions are still the same.
Thanks for your efforts here.
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Eddie im not sure why it surprises you that i like the astroplane,
an efficient dc shorted 1/2wave with current maxima higher above ground than a 5/8wave,
i wish id compared my old astro at the same tip height as other antennas on a 1/2wave mast the first time around,
37 years is not that long to get up to speed is it ?
its far from perfect, if it was tuneable that would be a big plus,
single piece legs hoop another plus,
a higher power rated feedpoint,
its also much stiffer in the wind than a 5/8wave,
big downside is the astroplane puts more wind load on your mast than any other vertical i can think of at the same tip height.
an efficient dc shorted 1/2wave with current maxima higher above ground than a 5/8wave,
i wish id compared my old astro at the same tip height as other antennas on a 1/2wave mast the first time around,
37 years is not that long to get up to speed is it ?
its far from perfect, if it was tuneable that would be a big plus,
single piece legs hoop another plus,
a higher power rated feedpoint,
its also much stiffer in the wind than a 5/8wave,
big downside is the astroplane puts more wind load on your mast than any other vertical i can think of at the same tip height.
Hi Bob.
I think most, if not all, of my 5/8^ GP that used four 9' radial and twice the vertical height of the AP had more wind load. But that's just me watching them in the wind...
I think most, if not all, of my 5/8^ GP that used four 9' radial and twice the vertical height of the AP had more wind load. But that's just me watching them in the wind...
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Homer,
a 5/8 is not twice the height with more wind load when mounted at the same tip height as designed,
my astroplane is mounted on a 12ft 1.5" mast inside about 7ft of scaffold pole so i can adjust the length above the isolator,
from the isolator to the tip of the astroplane hardly flexes at all in 50mph winds,
my other antennas use skinny tube & flop around in the wind,
the astroplane has more wind catching area & weight high up near the tip than other antennas mounted at the same tip height,
the bending moment at the isolator 5/8wave down from the tip is far higher with an astroplane than say the 1-10k.
a 5/8 is not twice the height with more wind load when mounted at the same tip height as designed,
my astroplane is mounted on a 12ft 1.5" mast inside about 7ft of scaffold pole so i can adjust the length above the isolator,
from the isolator to the tip of the astroplane hardly flexes at all in 50mph winds,
my other antennas use skinny tube & flop around in the wind,
the astroplane has more wind catching area & weight high up near the tip than other antennas mounted at the same tip height,
the bending moment at the isolator 5/8wave down from the tip is far higher with an astroplane than say the 1-10k.
I was happy to hear your good report just like you said, but I guess I was surprised considering your really good I-10K reports and posting the following.
Since you wish the antenna was made to tune...what kind of matching and resonance results are you seeing?
How high is it?
What is your <2.00:1 SWR bandwidth?
I find only one indication from Avanti in an ad dated 1978 in CB Magazine showing BW: "full 40 channels."
My notes show I was seeing <>3.40 MHz with my Old Top One recorded via the working feed line.
Thanks for the reports and keep us posted.
I have heard/read that the AP can be tuned by changes to the size of the cap hat, and by its fistance above the bracket.
Maybe modeling changes to the lwngth from tip to tip of the cap hat rods and the length of the vertical with the CH on it would indicate the truth of this claim.
Maybe modeling changes to the lwngth from tip to tip of the cap hat rods and the length of the vertical with the CH on it would indicate the truth of this claim.
My modeling has demonstrated this. Making the vertical element length to the cap hat shorter and lengthening the cap hat elements to compensate will lower the R value.
The DB
I would guess that most don't know what their <2.00:1 SWR bandwidth is, that is why I asked you.
My experience with the A/P design antennas I have is they show BW of 3.00 to 5.00 MHz when using a modest length low loss feed line.
I'll assume by your comments that your antenna is just showing a modest bandwidth, more typical of a high gain CB monopole ground plane with 1.00 to 2.00 MHz at best. I wonder if your more modest BW is due in part to the Isolation you added?
My model that is Isolated shows a more modest bandwidth too.
Maybe you should have bought a Sirio New Top One that was built to be more inductive and uses a gamma to add the necessary capacitance to reach resonance.
I'll ask Tib2K to confirm his bandwidth when he gets his new Old Avanti A/P installed. I think you both are going to be about 30' feet to the tip.
DB, what you claim maybe true, but I'm trying to keep my model true to the specs until it looks right. If Homer builds another home-brew of this A/P maybe he can incorporate tuning the radiator, top hat, and the two radials into his design...and check your idea out.
I just modeled Tib2K's dimensions and the model is showing a workable match, but the resistance is still a bit high with the construction I have. I will also play with your idea on this model...it needs tuning also.
I haven't tried tweaking the segment lengths yet, however the FS model for this construction does show an Average Gain very close to 1.00.
Homer, I know I can change the top hat lengths and it will change the reactance, but I'm not sure how it effects the resistance yet. I've probably done that already...just don't remember the effect on resistance.
I just suggested I would make such changes to my model and see if I get similar results to what Steve reports.