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Any Astro Plane Fans ?
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Thanks Homer, no doubt I was reading the wrong comments about the trick ghz24 showed DB.
When you built your PVC A/P using the dimensions in metrics from the Internet, do you recall having to make adjustments to tune?
When you built your PVC A/P using the dimensions in metrics from the Internet, do you recall having to make adjustments to tune?
Not at all. We experimented some with the spacing between the lower skirt, but it seemed not to matter much. Later I would read that the length of the upper vertical and cap hat size wouls make more of a difference. Never changed the cap hat to test it.
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"This antenna isn't what I know a lot of people think it is"
DB
most people on forums seem to claim the astroplane is just a 1/4wave groundplane,
we also have NB's theory its just a folded 3/4wave and should work with low vswr without any mast or feedline within the aperture of the basket,
id like to see the current distribution of the basket alone which is 20ft long with a source at the feed-point
i see it more like two tapered parallel 1/4wave transmission-lines sharing a common conductor,
one tapered 1/4wave line feeding a 1/2wave endfed radiator in parallel with a shorted tapered 1/4wave line.
DB
most people on forums seem to claim the astroplane is just a 1/4wave groundplane,
we also have NB's theory its just a folded 3/4wave and should work with low vswr without any mast or feedline within the aperture of the basket,
id like to see the current distribution of the basket alone which is 20ft long with a source at the feed-point
i see it more like two tapered parallel 1/4wave transmission-lines sharing a common conductor,
one tapered 1/4wave line feeding a 1/2wave endfed radiator in parallel with a shorted tapered 1/4wave line.
Where do you want the 1/4 wavelength section attached, the feed line side or the other, currently shorted side? If I put it on the side that is shorted, to get any currents to show on the wire, I will have to remove said short.
The basket alone? No upper radiator and no mast?
Essentially, this turns the antenna into a half wavelength loop, and has a very different current pattern than we would normally expect to see. Something to note on this model compared to the ones posted above is the peak current flow, which is less than 1/10 of some of the other models I posted above. In this case you have a current node, which is actually in the loop, and divided among the two electrical paths the loop provides. The feed point is at a current null.
I know you are asking to see a lot of different variations, but I really am failing to follow what it is you are looking for with these requests. Mind giving an explanation of your thoughts?
About the three explanations given... Wait, their are only two lines of thought? No 5/8 theory? No other theory? That is a surprise. Who are you guys and what have you done with the people who post on this forum?
I don't see how this antenna fits this description. Where is the ground plane, are people trying to claim that the basket is the ground plane? If the feed point were elsewhere, such as the upper vertical element, I could see this. However, as the feed point is where it is, and the resulting flow of current in the models, I just don't see this being the case.
I half agree with this statement. Following the current flow on my models, I definitely see a single 3/4 wavelength section that has a fold one one side of the feed point. This is supported, at least to some extent, by the "blue wire" I noticed above. That wire seems to have minimal currents, as well as a current flow that is out of phase with the feed point right next to it. The feed point seems to have no direct electrical connection from one side of this wire to the other.
I have to say, however, that I flat disagree with the no mast or feed line idea. It is true that both sides of the feed point will be directly connected to current nodes, however, those current nodes will be 180 degrees out of phase. One of the rules that I have learned about feed points is both sides are always in phase with each other. The modeling software will not violate this rule, it will change the current distribution of the model to force this rule, and it will look like this.
As we can see, we get a very different current distribution. It isn't shown here, but the R portion of the feed point impedance is also near 200, so their goes a naturally low SWR. When playing with the model, by making the upper vertical element shorter (literally to about an inch in length), and the capacity hat larger (I believe each of the four element were in the range of 110 inches in length) I was able to get R down to about 75. This model also has about 1 dB less gain than one with a mast of the optimal length.
I'm afraid I am not following your logic. I will have to think on this one.
The DB
yes the avanti advertising claim its 5/8wave DB, i posted why i think that could be, we may never know for sure why they claimed it unless somebody can show that it is somehow 5/8,
i don't see it in the electrical sense but physically when its on a 1/2wave mast yes its the same height as 5/8wave but has the advantage of current maxima been higher and no 1/8wave of out of phase radiation
Have faith in your no mast/coax model showing high vswr, it fits my real world test,
why am i asking for different models?
Im trying to establish what the radiator side looks like when looking into the bottom of the1/4 wave line on that side of antenna,
does it act like a 1/2wave endfed with a tapered 1/4wave shorted line in parallel with it ?
not sure how you would get current into the 1/2wave without something to push against in the model, you may have to add a mast to the opposite leg of the 1/4wave line
if you were to feed it with the other 1/4wave line via the hoop could the taper of the line smoothly transition from 50ohm to high impedance at the flared end to feed the 1/2wave leg with the parallel flared 1/4wave line inverting the short at the top end so it appears like an open circuit at the flared end ?
am i crazy ? lol.
i don't see it in the electrical sense but physically when its on a 1/2wave mast yes its the same height as 5/8wave but has the advantage of current maxima been higher and no 1/8wave of out of phase radiation
Have faith in your no mast/coax model showing high vswr, it fits my real world test,
why am i asking for different models?
Im trying to establish what the radiator side looks like when looking into the bottom of the1/4 wave line on that side of antenna,
does it act like a 1/2wave endfed with a tapered 1/4wave shorted line in parallel with it ?
not sure how you would get current into the 1/2wave without something to push against in the model, you may have to add a mast to the opposite leg of the 1/4wave line
if you were to feed it with the other 1/4wave line via the hoop could the taper of the line smoothly transition from 50ohm to high impedance at the flared end to feed the 1/2wave leg with the parallel flared 1/4wave line inverting the short at the top end so it appears like an open circuit at the flared end ?
am i crazy ? lol.
Unless I'm reading in Russian, it appears the software cannot deal with a 3/4 wave radiator shorted to the opposite side of the coax at the 1/2 wave point?
Also, DB, I was wondering about numbers, (regardless of the I-10K) - what were the two different AP heights above ground in the model?
...and no Bob, I don't think you're really all that crazy... we just won't mention that last post in public
Also, DB, I was wondering about numbers, (regardless of the I-10K) - what were the two different AP heights above ground in the model?
...and no Bob, I don't think you're really all that crazy... we just won't mention that last post in public
Electrical 5/8, nope. Physical 5/8, sure, but only due to luck on the size of the upper vertical element and cap hat. I noticed a fair number of claims from elsewhere (not this site) claiming it was a 5/8, and in some cases trying to show it. I was surprised that that claim wasn't also being made by at least someone here. I was actually almost joking with that statement.
I tend to have faith in my models unless I have reason to believe they are wrong. I would say the high SWR that my model is showing in this case was lower than I would have expected based on the antenna's lay out with no mast.
So basically, we are trying to use feed line to simulate the basket area of the AP? Did I get that part right? That would put the 1/4 wavelength section on the side of the feed point? OK, that gives me something to try and visualize...
As far as this conversation goes, I haven't figured that out yet...
I wouldn't say that the software can't handle it. I would say the software handles it differently than you seem to think it should, and I gave my thought on why I think the software handles it that way.
The model with the feed point at the same height as the I-10k would put the feed point at about 433 inches in height. The model that puts the tips at the same height would put the feed point at about 638 inches in height. The word "about" is used because one of the models is in meters and the other is in inches, and because of this the models didn't line up to the perfect inch.
I think I should also point out, to be thorough, that the I-10k model I made wasn't specifically made to the I-10k's specs, but was me playing with the "trombone" style of matching system, which I was able to make it work for any number of antenna lengths. It really is a versatile matching system that works with far more than 5/8 wavelength antennas. The antenna I used to compare it to was not actually a full 5/8 wavelengths in length as its tip is at 6.38 meters above the radials instead of 6.875 meters, which is 5/8 for a raw 11 meters. This length was used in that model because with this antenna and trombone matching system fully tuned, this is the length that modeling shows produces the most gain.
The DB
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I don't recall this experiment.
Do you mean you and I experimented with radial lengths on the A/P?
Did I do models or what?
OK. you never changed the cap hat, but did you have to change anything to effect the tune after it was built?
If you used your analyzer, did you keep any notes about the antenna match?
Since you were working with PVC which might have been larger diameter than the spec dimensions on the work sheet...did you compensate any?
Did your PVC A/P have a near perfect match near the middle of the CB band?
Do you have a real A/P?
I want to model using the metric spec sheet you used. But, I have hesitated on this one because the likely very wide bandwidth could allow a good match over a wide range in the real world. I'm not even sure this spec sheet was cut for the CB band in America.
Thanks again for your heads up.
DB
let me explain what i mean,
take your model with the mast, remove everything to the right of the mast including the hoop.
put the source at the bottom between mast & left hand leg so the source is looking into a 1/4wave shorted line,
what does it look like ?
let me explain what i mean,
take your model with the mast, remove everything to the right of the mast including the hoop.
put the source at the bottom between mast & left hand leg so the source is looking into a 1/4wave shorted line,
what does it look like ?
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is that adjusted for resonance of the 1/4wave line DB,
seems odd that adding the upper 1/4wave caused significant current to flow in the short at the top of the 1/4wave line when theres nothing flowing in the upper 1/4wave,
edit are the wires from source to antenna 7" each side lengthening the transmissionline off resonance ?
thanks
ps,
i meant the model with optimised 1/2wave mast since we know the astro does not like the mast ending up next to the hoop,
seems odd that adding the upper 1/4wave caused significant current to flow in the short at the top of the 1/4wave line when theres nothing flowing in the upper 1/4wave,
edit are the wires from source to antenna 7" each side lengthening the transmissionline off resonance ?
thanks
ps,
i meant the model with optimised 1/2wave mast since we know the astro does not like the mast ending up next to the hoop,
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