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ASTROPLANE best vertical antenna ever?


Mar 19, 2012
perfect ground?

8 dBi ?(looks like 7.87 to me) Could be because astroplane is a little directional.
Perfect ground inflates gain and hides the take off angle.
I have a dipole model at tip height of 36.25 ft , perfect ground gives it a gain of 8.04 dBi
Freespace gives the well known 2.15dBi
What height is the tip of your model at ?

Not saying that some model of the astroplane wont show better gain (or TOA) than a dipole but what you posted doesn't seem to.

Here is an adjustable astroplane model If anyone is interested in playing with it
CM 11 meter cb by ghz24
SY z=62.85974	'driven element length
SY rh=-86.8202	'ring height
SY zp=6.972382	'feed gap
SY rsf=0.413083	'changes ring diameter
SY ch=9.221404	'capacitance hat length
SY ml=-200	''mast length
SY pph=rh+(rh*-0.5)	'pinch point height
SY psf=0.97498
SY ppy=(30*rsf-zp)*psf
GW	1	1	0	0	0	0	-zp	0	0.48
GW	2	67	0	0	0	0	0	ml	0.75
GW	3	1	0	0	0	0	zp	0	.5
GW	4	7	0	zp	0	0	ppy	pph	.25
GW	5	7	0	-zp	0	0	-ppy	pph	.25
GW	6	7	0	ppy	pph	0	30*rsf	rh	0.25
GW	7	7	0	-ppy	pph	0	-30*rsf	rh	0.25
GW	8	9	0	zp	0	0	zp	z	0.25
GW	9	1	0	zp	z	0	zp+ch	z	0.25
GW	10	1	0	zp	z	ch	zp	z	0.25
GW	11	1	0	zp-ch	z	0	zp	z	0.25
GW	12	1	0	zp	z	-ch	zp	z	0.25
GW	100	1	29.99994*rsf	0*rsf	0+rh	27.7163225*rsf	11.4804889*rsf	0+rh	0.25
GW	101	1	27.7163225*rsf	11.4804889*rsf	0+rh	21.2131466*rsf	21.2131466*rsf	0+rh	0.25
GW	102	1	21.2131466*rsf	21.2131466*rsf	0+rh	11.4804889*rsf	27.7163225*rsf	0+rh	0.25
GW	103	1	11.4804889*rsf	27.7163225*rsf	0+rh	0*rsf	29.99994*rsf	0+rh	0.25
GW	104	1	0*rsf	29.99994*rsf	0+rh	-11.480489*rsf	27.7163225*rsf	0+rh	0.25
GW	105	1	-11.480489*rsf	27.7163225*rsf	0+rh	-21.213147*rsf	21.2131466*rsf	0+rh	0.25
GW	106	1	-21.213147*rsf	21.2131466*rsf	0+rh	-27.716323*rsf	11.4804889*rsf	0+rh	0.25
GW	107	1	-27.716323*rsf	11.4804889*rsf	0+rh	-29.99994*rsf	0*rsf	0+rh	0.25
GW	108	1	-29.99994*rsf	0*rsf	0+rh	-27.716323*rsf	-11.480489*rsf	0+rh	0.25
GW	109	1	-27.716323*rsf	-11.480489*rsf	0+rh	-21.213147*rsf	-21.213147*rsf	0+rh	0.25
GW	110	1	-21.213147*rsf	-21.213147*rsf	0+rh	-11.480489*rsf	-27.716323*rsf	0+rh	0.25
GW	111	1	-11.480489*rsf	-27.716323*rsf	0+rh	0*rsf	-29.99994*rsf	0+rh	0.25
GW	112	1	0*rsf	-29.99994*rsf	0+rh	11.4804889*rsf	-27.716323*rsf	0+rh	0.25
GW	113	1	11.4804889*rsf	-27.716323*rsf	0+rh	21.2131466*rsf	-21.213147*rsf	0+rh	0.25
GW	114	1	21.2131466*rsf	-21.213147*rsf	0+rh	27.7163225*rsf	-11.480489*rsf	0+rh	0.25
GW	115	1	27.7163225*rsf	-11.480489*rsf	0+rh	29.99994*rsf	0*rsf	0+rh	0.25
GS	0	0	0.0254
GE	0
GN	-1
EX	0	1	1	0	1	0	0
FR	0	0	0	0	27.18	0
It may not be to the original dimensions of the AP but it can be easily altered using the variables.
This one shows a gain increase over a dipole, only a little but its there .
How about a peek at yours?


Sr. Member
Sep 19, 2009
The gain of the 5/8 wave ground plane is heavily dependant on the ground plane under the vertical radiator. The radials on this antenna are far from an infinite ground plane but it is likely that the Penetrator would produce slightly stronger signals in the distance. The difference would not be noticed locally in most cases.

This assumes both antenna would be mounted at the same height. If you could get the Astroplane up significantly higher than the larger Penetrator, then in would likely be the winner all around. If you want a vertical with enough gain to see a noticeable difference, you'll need something like a Gain Master or Vector 4000.


Sr. Member
Sep 19, 2009
Avanti lied. No way a 1/4 wave ground plane can produce anything more than 2.15 dbi. Check out the Sirio specs, they tell the truth and place it right at unity gain. Avanti also gave the Sigma a 6.14 dbi rating. Seems like their standard gain figures just added about 2 extra db onto everything.
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Supporting Member
Mar 30, 2005
donald, i agree the astroplane has about the same gain as a dipole but i would like to see an astroplane in cst,

i see it as a hat loaded 1/2wave, an upside down modified j-pole/sleeve antenna

i imagine it radiates the same way as i think the sleeve on a sigma4 radiates via common mode currents on the outside of the legs,

down one leg across the hoop up the other leg is close to 5/8wave so antenna mode impedance will be pretty high with minimal current flowing in a 50ohm system,
when you add the mast you form a 50ohm transmission-line in parallel with the antenna mode impedance of the 5/8wave loop where significant transmission-line mode current will flow,

we know what happens whenever there is a phase or magnitude imbalance at the end of a transmission-line,

i think the 1/2wave mast is to minimise antenna mode mast currents in the same way an open sleeve or j-pole with a 1/2wave radiator surrounded by a 1/4wave sleeve will have little current flowing in the portion of radiator above the sleeve,
the antenna mode impedance of a 1/2wave is high and most of the current flows in transmission-line mode in the lower 1/4wave,

i will likely never find out if im right about the astroplane without a cst model since the avanti guys said to my great surprise in a magazine article that they did not understand exactly how it works.


Sr. Member
Sep 19, 2009
I will admit this antenna did surprise me a little bit when I put one into service many years ago. I've also heard many people say it worked like a 5/8 wave radiator. The part that downgrades my rating of the antenna is that Sirio is calling it a 1/4 wave ground plane at 2.15 dbi.

I don't put too much weight on the name they call it but the gain figure has some merit to me because they seem spot on with every one of their other omni antennas. I suspect they have used CST on most of their antennas. I also think they choose to share that marketing info on the antennas they have the biggest investments in.

Sooner or later I think CST will become more popular and we will find someone willing to test some of these ideas. With respect to Avanti, it's not hard for me to believe these guys got lucky a few times just bending radials in the field and stumbled into this effect by accident. At no time did Avanti even attempt to explain how the Sigma or Astroplane worked. Not a hint in the patents either.

I think you got the truth in the CB magazine article about the Astroplane and probably would have gotten the same answer for the Sigma. Except certain people that worked for the company still can't admit they didn't have a clue on how the Sigma worked.

One still claims Herb just made it because it looked cool. You would think these guys could look at the CST model today and figure it out....but no. Still in the dark just like the first day it went into production. I guess it's better to make something that works and not know why than to make something that doesn't and not know why.
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