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ASTROPLANE /Top One Ground Plane

Switch Kit

Switch Kit

Well-Known Member
Apr 6, 2005
3,595
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Do these base antenna's need a ground plane ? IM really not up on this antenna , would it be possible to some how place this antenna in a tree if need be ? Thanks for the help.Astroplane
 

edited by me cause i was wrong.
the antenna uses your coax and antenna mast as the counterpoise/groundplane. so no you dont need to add a groundplane just throw it up and your all set after tuning.


they say its kinda weakly built so make sure its mounted good. other than that put it were you want.
 
FL where did you get your information about the ground plane? Tell us what part of this antenna is the radiator if the bottom loop is a ground plane.

(Note from Moderator: This reply is in reference to an earlier post by FL that has now been edited, which is why it no longer makes sense. Marconi, let me know if you want this post deleted.)
 
The plot thickens ! Thanks guys ,tell me more. this is what the directions say ? ........Top One Ground Plane Antenna


Similar to the old Astro Plane antenna

10 Meter 26-30Mhz

2000 watt max power

Easy Assembly

Height : 11.5'

Top Radiation - This design results in increased range, fewer dead spots. This is especially important where installed height is limited. Radiates approximately 15' higher than most antennas which radiate at the bottom.

Lower Angle of Radiation - Your signal hugs the curvature of the earth instead of shooting your power up into the sky, which means greater distance than an ordinary omni-directional antenna.
 
Marconi said:
FL where did you get your information about the ground plane? Tell us what part of this antenna is the radiator if the bottom loop is a ground plane.
Click to expand...

well there 2 parts to every antenna ... right.
are you saying this antenna works different than any other.
blah..... either way he will have no problem sticking it up ina tree.
 
SK, don't put this one in a tree unless you can keep the branches and leaves out of the bottom ring. The bottom ring is not a ground plane and is a point of high voltage in this antenna.

They are not structurelly strong either so anything brushing by and touching the antenna may weaken it. If you want an antenna in a tree get an A99. A tree is a wind loaded support and they present a lot of lateral motion to any thing near the top. It will probably just tear the AP up in a short while.
 
OK I'm dumber than a coal bucket when it comes to this antenna, I have looked at them but would someone explain how they work. It looks like to me that the line would be dead shorted the way the thing hooks up? I know they work just wondering the deal behind them.
 
OK YJO, I wrote a letter to a friend some time back with my opinion. See what you think.
Jim, there are some variations in AP models. I think that Avanti originally built the AP a bit different than the one made much later that became popular. Maybe Antenna Specialist made some changes if they were ever involved with this project. However, I’m not real sure if AS was ever actually involved. There are some models out there that used a different mounting bracket design. I think they likely all work the same however.

The AP is a funny bird and was designed to allow for maximum radiation at the highest point possible within the limitations for height by the FCC. It is basically up-side-down, since the current node (at the feed point) is above the voltage node at the bottom loop in the antenna. For me this does not impose a limit to effectiveness at any particular low height it exhibits an advantage. On this issue is there is a lot of the erroneous BS about this antenna regarding height, and that it only works well when installed low to the earth.

The following is my opinion and is all take from an electrical point of view.

Electrically the AP uses a 1/4-wave feeder that works against a suitable ground to feed the radiating 5/8-wave antenna. Here a segment of the supporting mast or feed line is used as the ground element (just like in dipole except the shape is different). This ground element extends down from the current node near the feed point in the mounting hub for some distance below the bottom horizontal orbital ring of the antenna which originates the radiating element. In addition, since the feeder and the ground element (mast/feed line ie., ground element) remain relatively parallel in the vertical plan, there is virtually no radiation generated from this feeder or the ground element. The radiating portion of this antenna consists of three segments, (1) the originating 1/8-wave loop at the voltage node (the bottom loop in the horizontal plane), (2) another 1/4 wave element (similar to the 1/4-wave feeder) extending up from the loop at the bottom, and (3) at the top there is another 1/4-wave element that is shortened by the use of a 1/8-wave capacitance hat that is also in the horizontal plane. Thus you have a 5/8-wave, radiating element that is actually loaded near the top rather than near the bottom of the antenna.

This 1/4-wave feeder section theoretically does not radiate due to equal and opposite energy forces working between close proximity and parallel elements. This arrangement creates a condition that cancels out radiation in an action that works similar to the actions of current between the shielded and center conductor of your coax. This feeder is coax fed (in the hub at the feed point) at the beginning tip end of this element at a current node that is insulated from ground at this point. This configuration typically will NOT show us 50 ohm resistance at this point on a 1/4-wave element as you may know. The feed point impedance with a suitable counterpoise will be low in the range of 32 ohms of resistance at resonance just like any end fed 1/4-element working against a suitable ground. To raise (compensate) for this low input impedance the feeder is bowed in an arc ( ) | ), outward a bit from the ground affects side (mast/feed line), as noted above and in the symbol ( ) | ). With this ground element running parallel and along the side of this 1/4-wave tuned element 50 ohms resistance is derived. So, in affect this first section, the 1/4-wave element, is a fixed tuner for this antenna. Again, this arcing (mild bowing) of the element against the mast/feed line has the affect of raising the feed point resistance and is very important to understanding.

Again all of this process matches the feed line, at 50 ohms, very smoothly and nicely in the Astro Plane antenna. The exact physical length of all antennas longer than 1/4-wave length and that are end fed react this way and require some sort of matching device to be made purely resistive and resonant at the feed point. You will not find any other tuning or matching device in the AP and their feeder is unique.

If we take close note at the actual radiating element, it begins at the high voltage tip end of this tuner element where it attaches at the bottom hoop. As previously noted this hoop begins the physical radiating element, 1/8-wavelength, attached to another 1/4-wavelength element returning back up to the hub. Above the hub and directly connected to the bottom radiating element at the current node in the hub, you will find another 1/4-wavelength radiator that is shortened. This shortened section uses a cap hat to complete this electrically resonant device at a physical and non-resonant length, 5/8-wave length long. So it is referred to as a 5/8-wave antenna.

Notes: It is my opinion that this transition in matching currents through this long and smooth tuning element, the first 1/4-wave element, is the key to many good reports and is due to this genius in design. It creates a condition of minimum inductive reactance for the antenna to offset the additional load capacitance created by the excessively long radiator. The longer radiator is the sole feature that makes possible the increase in gain for all of these end-fed verticals that are longer than the typical 1/2-wave element. A tuner of similar design is also use in the Signal Engineering’s Quad antenna design.

To me this type of tuning and matching has the direct affect of considerably reducing the bad actions associated by common mode currents (CMC) on the feed line and/or mast that may produce some additional local RF interference found in other GP antennas. This also has the affect of eliminating much vertical ground noises as well. I do not wish to get into the business of common mode currents here, but CMC elimination is only one of the important aspects of why I feel this simple, but complicated little antenna; works so well.

Regarding the horizontal notations above: This is a vertically polarized antenna, but the presence of some horizontal radiating elements, in my opinion, enhance, in particular, the DX qualities of this very efficient radiator. On the other hand it may be said that this also may cut down on some of the vertical ground wave action in the antenna. As a result it may have some attenuating characteristics that polarity differences are known to make. This feature in the AP may also account for its quite noise floor operations as well; a factor, which more or less, stands alone by the many consumer accounts of the actions for this unique but very effective antenna.

Just try this antenna high up there one day and watch it talk as big or bigger than any and for sure when DX is really rolling.

Jim, I did not proof read this close. If I find errors, I will let you know.

Marconi
Click to expand...
 
Thank you all for the input on this Top-One / copy of the Astro-Plane. Surely a strange and different kind of antenna for sure. This one is only 10.5 feet high as well, my friend has talked on this antenna in the past off a 20 foot push up pole and surprising did very well on it, locally he always seemed to hold his own on about 150 watts on the side. He always said that he had the best of times shooting skip on it as well. He has resently moved and can't have a antenna outside his mobile home , but he does have a very large tree right out side his place , it looks like this one won't work in the tree to very well )-: looks like he needs to get a imax or a 99 for his troubles. Thanks again all.
 
SK, I don't mean to imply that the AP won't work well in a tree. I only mean that the constant lateral motion of a tree might be rough on the antenna, as it will for any antenna with lots of parts to come loose or break.

Sure it will work up there just fine. It is a cheap antenna, if your buddy has one and wants to put it in a tree then have at it. That would be cheaper than going out and buying an A99 and it might even work a little better with skip. It surely will most often be quiter when conditions are pretty quite. He will notice that, I'm sure.

Just keep us posted at his progress in the project, OK?
 
Thank you very much Marconi , the tree is well noted and thank you for all your help on this one. Switch Kit
 
I had one for a while, it was phenomenal for skip. A bit flimsy, it could do with better hardware and higher quality aluminum stock, but it did fine in the wind and ice here in IL winter.

It doesn't need to be tuned for resonance, either. Mine was most resonant at 27.000, with about a 2 Mhz bandpass below 1.8 to 1 SWR (26-28 ).

Price was pretty good, too. I think I got it from Pacific CB for about 50 bucks plus shipping. Easy to assemble, easy to mount, too. I traded it for an Imaxx 2000, I seem to hear my locals a little better, but they don't notice much difference on me. I'd say the two antennas are comparable performance-wise.
 

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