New style astro plane

[freecell]

"i say 1/4 wave folded dipole."

from the patent:

ABSTRACT: a communications antenna which includes a vertical conductive mast and a pair of one-quarter wavelength conductors extending downwardly from a first reference level (top bracket) to a second reference level. (the loop) the conductors are electrically connected at the second reference level and one of the conductors is electrically connected to the mast at the first reference level. a one-eighth wavelength conductor extends upwardly from the first reference level and is electrically connected to the mast at the first reference level. the one-eighth wavelength conductor is capacitively loaded at its top to act as a one-quarter wavelength conductor........

add them up.

 

[Master Chief]

add them up.

1/4 + 1/4 = 1/2

1/2 + 1/8 (conductor above first reference level) = 5/8

5/8 + 1/8 (capacity hat) = 3/4 (required to match to 50 ohm coax)

The capacity hat is in the horizontal plane so the vertical radiating element is only 5/8.

Its a 5/8 wave antenna!

 

[Master Chief]

coating the threaded end of the element with some automotive tune up grease will greatly ease the installation and assure a tight fit while maintaining conductivity.

Actually, "tune up grease" is a DIELECTRIC. It works good by sealing around electrical connections by keeping air, dirt, and moisture out. BUT, it is NON-CONDUCTIVE!

Usually this dielectric grease will be squeezed out of the electrical joint so a reliable electrical connection can be made, while the freshly squeezed grease seals that connection.

You did mention to use just a thin film which is a good idea, but I wouldn't use this on any of the aluminum that will be making an electrical connection! I'd use Noalox instead. However, the dielectric tune-up grease would be fine on the aluminum that is only touching the insulator.

Permatex Dielectric Tune-Up Grease

 

[Captain Kilowatt]

Master Chief, I have been using the silicone dielectric grease on antenna connections for years and years with no problems. Andrew corporation even reccommends it for use on their heliax cable connectors and not just for the O-rings either.I usually use a star washer between pieces so it bites into the aluminum nicely. Even on the parts that have no star washers I have never had a problem,the connection has stayed good for years.I find that the grease prevents the aluminum from oxidizing and that is what keeps the connection in good shape.I was using it years before Noalox was available here.Now I use Noalox sometimes and the silicone grease sometimes.It all depends which I find in the mess I have first.

 

[Master Chief]

I've used Andrew's dielectric on the connectors I've installed also. I use it mainly on the O-ring. I use "STUF" inside of the connector.

I just want the users to be aware that this grease is NON-CONDUCTIVE and should be used sparingly!

The way spark plug wires "snap" together displaces the grease enough to make a good electrical connection.

 

[freecell]

The capacity hat is in the horizontal plane so the vertical radiating element is only 5/8.

Its a 5/8 wave antenna!

not to be argumentative and solely for the benefit of others beside ourselves, you do realize that the distinction that you make between the vertical portion of the uppermost radiator and the top hat (in the horizontal plane) is unimportant when determining the total electrical length of the active element both in terms of input impedance and resonance. you as much have conceded to that in this portion of your prevous post.

"5/8 + 1/8 (capacity hat) = 3/4 (required to match to 50 ohm coax)"

however i do detect a certain amount of marketing strategy on avantis part in referring to the astroplane as a 5/8 wave antenna. 5/8 antennas were all the rage at the time and everyone had to release their own interpretation, whatever shape or form they may have taken and it's difficult to release the next newer, better and improved model when the slot has already been filled (as in the case of the coming Sigma4) and as i see it this may have been the primary reason why they chose not to classify the antenna in electrical terms according to wavelength. as long as we don't confuse this "strategy" with the correct electrical properties then pretty much the way i feel about it is you say potato and i say patato. the guys at avanti were still ahead of their time even back in the 70's.

 

[Cat Driver]

Good thing you guys weren't in the advertising dept of avanti. You'd have us poor saps so confused on this antenna you probably wouldn't sell 10 of'em.


Ronnie

 

[Master Chief]

If we marketed antennas for Avanti, we wouldn't tell you all of this and come up with some real cool terms you could use on your friends to make you look smart! 8)

I am a HUGE fan of Avanti antennas. I've never pretended to completely understand the Astroplane in the past, but I have a firm handle on it now.

The Astroplane's claim to fame was being able to get it up higher than a regular 5/8 groundplane. A 5/8 radiates most of its energy from the bottom of the antenna where the Astroplane's compact design gets that radiation characteristics up higher.....if you follow the 60' rule.

Everyone I know who used an Astorplane LOVED it!

Speaking of getting the current up the element, this is what Eddie at Wolf Antennas says he does by putting "loops" up on the main element. I'd send you to his website, but it has been suspended.

 

[bob85]

i fancy trying one with a full 1/4wave radiator ( no caphat ) as described in the patent,

one thing i find odd is the 27-29.7mhz rating,
it claims the lengths are just under 1/4wave at 29.7mhz so the antenna performs best there,
is the astroplane as it came from the shop tuned up there or did they recenter it on 27mhz?

where does the 1/8wave of loop figure in the electrical length and does it shift phase angle between the vertical elements?

 

[Master Chief]

OK, now its a 7/8 wave!

 

[loosecannon]

from what i understand, the loop doesnt have to ba a loop to serve its purpose in this antenna.
if you were to take half of it away, it would still work fine.

i think its just about creating an electrical connection between the vertical elements at the bottom while keeping it away from the center "element".

as always, i could be wrong.LOL

i dont know enough to argue about what kind of antenna it is, i just heard that it was a folded dipole.

anyway, great antenna, love mine.
will probably always own one.
loosecannon

 

[W5LZ]

...reminds me a lot of an 11 meter 'J' pole.
- 'Doc

 

[freecell]

it might be a folded 1/2 wave dipole if you ignore section 46 (the uppermost 1/4 wave element) and forget about the fact that there is no feed connection at either end of the center of elements 16 & 18. it is NOT a balanced feed design. the feed is offset and the total electrical conductor length is 3/4 wavelength with the feedpoint located at a 1/4 wave point between elements 46 and 16. since the offset feed represents unbalanced currents in the two halves of the conducting element (1/4 wave top and 1/2 wave below) the use of a current balun is not required.

the loop represents a value of inductance required to supply the missing physical length of the 1/4 wave elements at 16 & 18. removing half of it is not recommended. its effects on values of Z and X as well as pattern symmetry is unavoidable.

there's no such thing as a 1/4 wave dipole, folded or otherwise. a folded 1/2 dipole is nothing but a closed and closely spaced full wave loop and as such represents too high of an impedance for direct feed using 50 ohm line.

 

[SmackDown]

...so the astroplane remains a puzzle sealed in a cunundrum wrapped in an enigma...

can anyone definitively say what it is.....

those Avanti engineers sure knew how to party

 

[loosecannon]

well, this thread is getting long, but what the heck, someone's gotta discuss this antenna ad nauseum; might as well be us!LOL

i used freecell's link to look at the patent sheets, and i must say, WOW! how informative!
havent gotten an opportunity to peruse them until now.

here are a few direct quotes from the patent sheet that kind of have to do with the things we are discussing in this thread.
namely, electrical length, polarization, etc...


1. as for the contention that the antenna has some horizontal polarization characteristics; i cant refute the notion that it does, but i think the assumption might be due to a misinterpretation of the patent sheet.
here's what it says:
"the antenna shown in figures 2-5 is shown to be vertically oriented which for many uses is the most desirable, for example for CB use. however, it is clear that it may be horizontally oriented, and may, therefore be supported by a horizontal boom member rather than the vertical boom member or mast 14. in such a construction, the horizontal planes or levels A and B would then be vertical parallel planes or levels."

to me this means that you can mount the antenna sideways if you want a horizontal pattern; not that the vertical antenna itself has horizontal radiation properties.


2. the electrical length of the antenna. this will refer to page three of the patent sheet for the diagrams:

"the electrical circuit of the antenna in fig. 2 is illustrated schematically in fig.5. dimentions A and B are each one quarter wavelength in electrical length, although, as stated above, conductor 46 may be actually shortened by capacitively loading the antenna at its top."

to me, this says that this is a half wave antenna.

unless the vertical boom member which extends downward from the hoop is considered part of the radiating element, which would make it a 3/4 wave antenna.
i do not believe that to be the case, but do not know near enough about this stuff to say so for sure.

the part referring to shortening the top conductor by capacitive loading is what the final design of the antenna reflected.
they must've been toying with the idea of using a full length 1/4 wave radiator up top, but decided on the capacity hat to keep the antenna height down, as well as a lower take off angle. after all, this antenna's main marketability was the fact that it could get out further while maintaining the 20' max height limit over existing structures.

BTW, they say in the patent sheet that increasing the length of the top radiator to 1/4 wavelength and eliminating the horiz. radials will raise the take off angle, but that capacitively loading it decreases the efficiency a bit.
the patent states that the antenna will operate over a wider bandwidth when a full 1/4 wavelength top radiator is used.
interesting!


one thing that i found neat was the fact that instead of using the top radiator that comes with the antenna, you could extend the mast 4 feet above the top bracket, add the horizontal elements and be on the air!

could be cool to know if your antenna gets damaged in a storm, or if you are building your own. (some guy i know just built his own. says it works great!)

i think building one of these for 20 meters would be SO cool!
can you imagine what it would look like?
people would trip out when they saw it on your house!!!
just double the size of it!


anyway, whaddaya think?
loosecannon