I personally can not prove this, but some say that an open ended end hat can see up to double the effectiveness by attaching a ring or skirt from the ends of the wires to each hat wire to the other.
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homebrew astroplane build
- Thread starter loosecannon
- Start date
if you wire them together at the tips you increase loading so you would have to reduce the diameter to get back to the same resonant frequency.
LC, here are 3 models.
1. The A/P I started with as a base line to compare the match for each model.
2, The same model as #1 with wires added between the tips on the Top Hat. Not tuned.
3. The same model as #2 with the top hat adjusted back to resonance.
I added Overlays for each model to compare pattern and maximum gain.
1. The A/P I started with as a base line to compare the match for each model.
2, The same model as #1 with wires added between the tips on the Top Hat. Not tuned.
3. The same model as #2 with the top hat adjusted back to resonance.
I added Overlays for each model to compare pattern and maximum gain.
thank you so much for making those models Marconi!
looks like it lowered the gain just a little bit (comparing models 1 and 3), and also looks like it pushed that top lobe down just a bit.
looks to me like there is not much to gain there, and that the juice ain't worth the squeezin'.
does your modeling program allow for different diameters for the mast/ center conductor?
since i will be using a fiberglass mast, essentially my "mast" will only be 1/4" in diameter, or 1/2" if i go with the fat coax.
my concern with this is bandwidth.
super cool to have those models. thank you again for that.
LC
looks like it lowered the gain just a little bit (comparing models 1 and 3), and also looks like it pushed that top lobe down just a bit.
looks to me like there is not much to gain there, and that the juice ain't worth the squeezin'.
does your modeling program allow for different diameters for the mast/ center conductor?
since i will be using a fiberglass mast, essentially my "mast" will only be 1/4" in diameter, or 1/2" if i go with the fat coax.
my concern with this is bandwidth.
super cool to have those models. thank you again for that.
LC
Model #2 is what I got just by adding wires to the ends of the existing top hat radials and it shows the effects to the match and the pattern. The maximum gain does go up as reported, but in this case the gain value is at a high angle. Models report maximum gain at the maximum TOA and you have to watch and compare the patterns to be sure.
Well LC the models do tend to show little differences, but testing in the real world is required to really be able to tell for sure.
Yes.
Your mast diameters are very small for plastic or metal in the CB band. Maybe you are planning a high frequency model that is much smaller. Maybe small enough to stand up with a non-conductive mast and using the coax shield as the conductive radial mast in your case while using small diameter plastic for support.
If so, why don't your give me all the dimensions for your idea including the center frequency, installed height at feed point, tubing material and diameters.
thanks for the reply Marconi.
No, this is just going to be a regular old CB antenna.
It's the CTE top one astroplane copy. (not the 1/4 wave gamma fed thing that came out later) this is the one that is a pretty much 100% copy of the astroplane design.
it's all made of 1/2" aluminum tubing except for the upper vertical 4 foot section that is either 3/4" or 1" in diameter, i can't remember.
the only things that are going to be different from a typical astroplane installation is that im going to use a non-conductive mast, and im going to choke the coax at the proper place with snap on ferrite chokes.
because of skin effect, and me not knowing how changes in "mast" diameter affect the tuning of the antenna; im a bit concerned that using the coax braid as the "mast" will cause the antenna to either be out of tune, or very narrow banded.
i guess the way this would translate to your antenna modeling software would be that you would input your "mast" diameter at .25 inches and model that.
then do one where the mast is .5 inches and see how that changes things.
we may find that the antenna won't tune well until you get the mast up to say an inch in diameter.
who knows...
once again thanks for all your effort and advice.
LC
No, this is just going to be a regular old CB antenna.
It's the CTE top one astroplane copy. (not the 1/4 wave gamma fed thing that came out later) this is the one that is a pretty much 100% copy of the astroplane design.
it's all made of 1/2" aluminum tubing except for the upper vertical 4 foot section that is either 3/4" or 1" in diameter, i can't remember.
the only things that are going to be different from a typical astroplane installation is that im going to use a non-conductive mast, and im going to choke the coax at the proper place with snap on ferrite chokes.
because of skin effect, and me not knowing how changes in "mast" diameter affect the tuning of the antenna; im a bit concerned that using the coax braid as the "mast" will cause the antenna to either be out of tune, or very narrow banded.
i guess the way this would translate to your antenna modeling software would be that you would input your "mast" diameter at .25 inches and model that.
then do one where the mast is .5 inches and see how that changes things.
we may find that the antenna won't tune well until you get the mast up to say an inch in diameter.
who knows...
once again thanks for all your effort and advice.
LC
it will be interesting for sure Homer, but without any real way to quantify any changes or alterations i make, i will really only be able to say "it works pretty good" or "i think it's worse than my IMAX" LOL.
if i start changing things, im going to be 100% trusting what the modeling software says about what im trying.
i know im posting the same portions of the patent sheet that we have all read, but just for convenience sake, here is the portion of the sheet that has me most concerned:
"Although in normal use the boom member 14 will be quite long, it has been found that the takeoff angle of the signal at maximum strength tilts upwardly more as the first conductor 14 decreases in length from one-half of the wavelength on which the antenna is intended to operate.
Stated another way, the first conductor 14 should preferably project beyond level B a distance at least equal to about the length of conductors 16 and 18. When the length of the first conductor 14 is so dimensioned, the takeoff angle at maximum signal strength is optimized for such as CB use and the like.
It will be apparent, however, that where a steeper takeoff angle at maximum strength is to be desired in other environments, the length of conductor 14 may be reduced. It will be observed that conductors 16 and 18 flare outwardly and downwardly. Their relative diameters and the spacing of them from each other and from the mast, as well as the flare, controls the impedance at c, d (FIG. 5).
This impedance preferably is 50 ohms in accordance with the typical construction described and for CB use. However, the diameters of the parts, the spacing and the flare may be varied to obtain either different impedances or the same impedance via variance of diameters, spacing and flare in a manner that will be understood by those skilled in the art for the antenna to operate most efficiently. It has been found, however, that the flare affects not only the impedance, but also influences the takeoff angle at maximum signal strength.
The flare of the construction described hereinafter provides a takeoff angle that is about the maximum reasonably allowable for most efficient CB use of this antenna. When the flare was omitted and the conductors 16 and 18 were tested parallel to the first conductor 14 it was found that the takeoff angle at maximum signal strength was as much as 10 to 15° below the horizontal.
Although for certain uses, such a downward tilt may be desirable, it appears that the optimum disposition of conductors 16 and 18 lies between the parallel positioning of straight conductors 16 and 18 and the flared positioning of flared conductors 16 and 18 with respect to the conductor 14, as described in conjunction with the specific embodiment illustrated in the drawings."
so basically as soon as i start changing the distance between 16 14 and 18, im messing with the impedance and the take off angle.
i think im going to have to go off of whatever the models show for these changes.
if it looks like its going to cause trouble, i'll probably go back to using a telescoping metal mast about 30 feet long. it won't reach the ground though.
it will be about 12 feet up to the bottom of the mast.
it might be neat to see the changes made from changing nothing but the hoop diameter also, as we know that a parallel 16 14 18 relationship makes a below the horizon TOA according to the patent.
LC
if i start changing things, im going to be 100% trusting what the modeling software says about what im trying.
i know im posting the same portions of the patent sheet that we have all read, but just for convenience sake, here is the portion of the sheet that has me most concerned:
"Although in normal use the boom member 14 will be quite long, it has been found that the takeoff angle of the signal at maximum strength tilts upwardly more as the first conductor 14 decreases in length from one-half of the wavelength on which the antenna is intended to operate.
Stated another way, the first conductor 14 should preferably project beyond level B a distance at least equal to about the length of conductors 16 and 18. When the length of the first conductor 14 is so dimensioned, the takeoff angle at maximum signal strength is optimized for such as CB use and the like.
It will be apparent, however, that where a steeper takeoff angle at maximum strength is to be desired in other environments, the length of conductor 14 may be reduced. It will be observed that conductors 16 and 18 flare outwardly and downwardly. Their relative diameters and the spacing of them from each other and from the mast, as well as the flare, controls the impedance at c, d (FIG. 5).
This impedance preferably is 50 ohms in accordance with the typical construction described and for CB use. However, the diameters of the parts, the spacing and the flare may be varied to obtain either different impedances or the same impedance via variance of diameters, spacing and flare in a manner that will be understood by those skilled in the art for the antenna to operate most efficiently. It has been found, however, that the flare affects not only the impedance, but also influences the takeoff angle at maximum signal strength.
The flare of the construction described hereinafter provides a takeoff angle that is about the maximum reasonably allowable for most efficient CB use of this antenna. When the flare was omitted and the conductors 16 and 18 were tested parallel to the first conductor 14 it was found that the takeoff angle at maximum signal strength was as much as 10 to 15° below the horizontal.
Although for certain uses, such a downward tilt may be desirable, it appears that the optimum disposition of conductors 16 and 18 lies between the parallel positioning of straight conductors 16 and 18 and the flared positioning of flared conductors 16 and 18 with respect to the conductor 14, as described in conjunction with the specific embodiment illustrated in the drawings."
so basically as soon as i start changing the distance between 16 14 and 18, im messing with the impedance and the take off angle.
i think im going to have to go off of whatever the models show for these changes.
if it looks like its going to cause trouble, i'll probably go back to using a telescoping metal mast about 30 feet long. it won't reach the ground though.
it will be about 12 feet up to the bottom of the mast.
it might be neat to see the changes made from changing nothing but the hoop diameter also, as we know that a parallel 16 14 18 relationship makes a below the horizon TOA according to the patent.
LC
LC, the metal mast does not need to reach the ground. It only needs to be metal from the top mounting bracket through the bottom ring and descend for a minimum of the combined length of the total of the distance of the antenna from the bottom ring to the top of the antenna, or at least 12 feet sticking down below the ring to a preferable length of 1/2 wavelength of the operating frequency.
It needs to ideally be on a conducting mast of 24', or minimally of 20'.
It needs to ideally be on a conducting mast of 24', or minimally of 20'.
Also, the diameter of the mast will affect impedance because it will change the spatial relationshipbetweenconductors 14, 16, and 18, so the antenna may tune somewhere other than within the 40 channel CB band.
So, well, there it is...
So, well, there it is...
i was just making sure i mentioned that the mast didn't go all the way to the ground so that i didn't confuse anyone.
im sure we both know that we definitely don't want our metal mast to be on the ground as it would then turn the antenna into a leaky capacitor.
LC
ok well here's some information that gives me a little more assurance that my idea (well actually their idea LOL) can work.
i've included an extra paragraph or two at the end just because it gives dimensions and might be of use to someone reading this thread.
"Of course, as explained, coaxial cable feed connections 38 and 40 are made to the clamp assembly and to the split brass ring and the cable 37 itself is suitably taped to the mast. It has been found that when an outer braided conductor forms the cover of the coaxial cable, this may serve as the first conductor. In such a case, the conductive mast 14 may be omitted and a non-conductive support substituted therefore. When that is done, it is important to make certain that the coaxial cable is positioned and centered properly with respect to the other conductor members described."
here is the part with the dimensions:
"A typical antenna now being made and marketed in accordance with the principles of this invention is adapted to be mounted to a mast 14 which may be a 20-foot steel or aluminum mast and which may be 1 % inches in diameter. A 4 foot section of one-half inch aluminum tubing which is flat at one end is provided with four 2-foot radial aluminum tube members each of which is three-eighth inch in diameter.
Each is flattened at one end and bored to facilitate securance to the 4-foot section and to project radially therefrom to constitute conductor 46. The 4-foot section comprises conductor component or portion 47 and pairs of the 2-foot sections comprise the transverse component or crossed conductors 48, 50. A pair of clamping elements 25 of aluminum are provided. Two 8-foot sections of one-half inch diameter aluminum tub ing are positioned in the end portions 28, 30, one of the two 8 foot sections (conductor 16) being proportioned to receive the end of conductor portion 47 at the clamp members and in end portion 28.
Each of the 8-foot sections is fabricated from a pair of 4-foot sections of tubing which sections are secured to each other at adjacent ends. These 8-foot sections then comprise conductors 16 and 18 and are clamped in end portions 28 and 30 constructed as described previously. From center-to-center, conductors 16 and 18 in end portions 28, 30 are spaced apart approximately 6 inches. At the time conductors 16 and 18 are clamped in the clamp assembly 24, conductor 46 is secured to the clamp assembly and made electrically integral with conductor 16.
Next, two pairs of three-eighth inch aluminum tubing each piece being bent to a 90° arc are secured to each other by fasteners and by loop clamps and to the lower ends (level B) of the 8-foot sections 16 and 18. This then provides a circular loop segment electrically connecting the lower ends of conductors 6, 18 to each other and at a distance of about 30 inches center-to-center. Intermediate their lengths, i.e., at the 4-foot point, sections 16 and 18 are provided with a spreader clamp assembly 22 which includes a fiberglass rod 41 approximately 13 inches in length and three-eighth inch in diameter.
This is secured to mast 14 by a stainless steel loop clamp 39 and to each of conductors 16 and 18 by loop clamps 43. From center-to-center, conductors 16 and 18 are each spaced apart about 12 inches center-to-center on opposite sides of mast 14. Of course, prior to securing the fiber glass rod to the mast, a U-bolt clamp 26 is positioned about the mast at the clamp assembly 24 to mount the antenna to the mast. Thereafter the fiber glass rod is secured to the mast. The clamping and pro portioning provides a significant flare of the conductors 16, 18, which as previously described, influences both takeoff angle and impedance. The takeoff angle and impedance may be varied or altered, as described hereinbefore."
LC
i've included an extra paragraph or two at the end just because it gives dimensions and might be of use to someone reading this thread.
"Of course, as explained, coaxial cable feed connections 38 and 40 are made to the clamp assembly and to the split brass ring and the cable 37 itself is suitably taped to the mast. It has been found that when an outer braided conductor forms the cover of the coaxial cable, this may serve as the first conductor. In such a case, the conductive mast 14 may be omitted and a non-conductive support substituted therefore. When that is done, it is important to make certain that the coaxial cable is positioned and centered properly with respect to the other conductor members described."
here is the part with the dimensions:
"A typical antenna now being made and marketed in accordance with the principles of this invention is adapted to be mounted to a mast 14 which may be a 20-foot steel or aluminum mast and which may be 1 % inches in diameter. A 4 foot section of one-half inch aluminum tubing which is flat at one end is provided with four 2-foot radial aluminum tube members each of which is three-eighth inch in diameter.
Each is flattened at one end and bored to facilitate securance to the 4-foot section and to project radially therefrom to constitute conductor 46. The 4-foot section comprises conductor component or portion 47 and pairs of the 2-foot sections comprise the transverse component or crossed conductors 48, 50. A pair of clamping elements 25 of aluminum are provided. Two 8-foot sections of one-half inch diameter aluminum tub ing are positioned in the end portions 28, 30, one of the two 8 foot sections (conductor 16) being proportioned to receive the end of conductor portion 47 at the clamp members and in end portion 28.
Each of the 8-foot sections is fabricated from a pair of 4-foot sections of tubing which sections are secured to each other at adjacent ends. These 8-foot sections then comprise conductors 16 and 18 and are clamped in end portions 28 and 30 constructed as described previously. From center-to-center, conductors 16 and 18 in end portions 28, 30 are spaced apart approximately 6 inches. At the time conductors 16 and 18 are clamped in the clamp assembly 24, conductor 46 is secured to the clamp assembly and made electrically integral with conductor 16.
Next, two pairs of three-eighth inch aluminum tubing each piece being bent to a 90° arc are secured to each other by fasteners and by loop clamps and to the lower ends (level B) of the 8-foot sections 16 and 18. This then provides a circular loop segment electrically connecting the lower ends of conductors 6, 18 to each other and at a distance of about 30 inches center-to-center. Intermediate their lengths, i.e., at the 4-foot point, sections 16 and 18 are provided with a spreader clamp assembly 22 which includes a fiberglass rod 41 approximately 13 inches in length and three-eighth inch in diameter.
This is secured to mast 14 by a stainless steel loop clamp 39 and to each of conductors 16 and 18 by loop clamps 43. From center-to-center, conductors 16 and 18 are each spaced apart about 12 inches center-to-center on opposite sides of mast 14. Of course, prior to securing the fiber glass rod to the mast, a U-bolt clamp 26 is positioned about the mast at the clamp assembly 24 to mount the antenna to the mast. Thereafter the fiber glass rod is secured to the mast. The clamping and pro portioning provides a significant flare of the conductors 16, 18, which as previously described, influences both takeoff angle and impedance. The takeoff angle and impedance may be varied or altered, as described hereinbefore."
LC
Hi Marconi,
I took my CTE Top One out of the box and confirmed your measurements.
yes, that is the antenna i have. sorry if i was misleading with my guesses on tubing diameter.
thanks!
LC
I took my CTE Top One out of the box and confirmed your measurements.
yes, that is the antenna i have. sorry if i was misleading with my guesses on tubing diameter.
thanks!
LC
LC, have you really figured out how you will be able to support your CB Top One with a skinny 0.25" plastic mast and get any height above Earth?
Model below:
1. is the Real Earth model @ 36' feet with a 0.242" inch diameter LMR 240 coax and no mast, just the coax for the antenna conductor.
Model below:
1. is the Real Earth model @ 36' feet with a 0.242" inch diameter LMR 240 coax and no mast, just the coax for the antenna conductor.