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Avanti Astro Plane (old school)

JPT

JPT

BANNED
Oct 15, 2006
38
0
16
N.W. Corner
I recently went and knocked on the front door of a old man that I had helped install this antenna MANY years ago, as a kid. This gentleman has since passed away & his son lives there now. We chatted for awhile about the CB craze of the 70's and he asked me if I would help him take it down, since he was having the roof replaced soon. I agreed to come back tomorrow. He offered the antenna to me, to which I agreed, lol.
I had one of these 20 years ago myself & was always impressed with the low SWR's across the regular 40 band. How broadbanded are these original astroplanes?, as I did not have a radio that had alot of frequencies back then. I found online they will handle approx 2K, which is fine, since my 4-400 does 1600 PEP max. I will be using new LMR 400 coax & giving this a complete onceover before installing in a 80 ft tree on my property. This will be a great antenna to do field studies with, once I get my Interceptor 10K assembled & installed in a adjacent tree at the same height. Any input & ideas would be appreciated, JPT.
 

I have started my testing with this antenna, before it goes up in a tree. I am getting good reports locally & have great receive on 11 meters. The SWR's are high on 11 meters 2.2.1 (27.055) & absolutly flat on 29.435. Is there any adjustment (fiberglass hub) on the Astroplane to see if I can get the SWR's lower on 11 meters?
 
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all you need to do is find a way to lengthen the antenna over all some to get the swr down on 27mhz. is it a 2 peice,? 3 peice.? maybe were the antenna is put together you can lenghten it out there. probably need to lengthen it 1 inch or so.
 
Thanks for the input. This is a unique antenna design for sure. I am going to see if Marconi, Bob, have to say before I mess with it, JPT.
 
hi JPT,

ok, first, you probably already have this info, but if not; make sure you have the antenna assembled according to the specs in this manual:

http://www.cbtricks.com/ant_manuals/ant_spec_avanti/astro_plane.pdf


as for lowering the SWR, if the SWR isnt about 1.3 to 1 on the CB band, then there is something wrong with the installation. these antennas are made to not need adjustment and will give a very low SWR on the CB band when assembled and installed properly.

yes, you can adjust the SWR by extending or shortening the two lower legs that connect to the hoop at the bottom, but you really shouldnt need to.

the most common problems people encounter with this antenna design is that they dont have a good metal to metal connection from the top mast mounting bracket and the mast, and that the mast is not long enough.

so:

1. make sure you have good metal to metal contact from the upper mast mounting bracket and the mast. (remove all paint from the mast in this area)

2. the mast needs to extend down past the hoop for at least 8.5 feet, and there needs to be good metal to metal contact between all mast sections.
in essence, you need one solid metal pole that goes from the top mast mounting bracket of the antenna all the way down 8.5 feet below the hoop.
i think that equals out to about 16 feet of mast.
the mast is actually part of the radiating system.

3. make sure your coax runs straight down the mast all the way down to 8.5 feet below the hoop. (again, about 16 feet or so)

4. you should secure the hoop to the mast with four lengths of UV resistant rope or monofilament.
this is to keep the mast in the exact center of the hoop.
this is important for two reasons.
A) when the mast gets close to one portion of the hoop and further from the opposite portion, the SWR will fluctuate.

B) if the hoop is allowed to sway in the wind long enough, it will eventually break the aluminum legs that hold it to the antenna.


good luck,
please let us know what you find,
LC
 
Thanks for the input LC & Mojo, I contacted Bob-85 via paltalk & he gave me the manual & patent files today. I changed out the coax & got the SWR to read at a 1.7.1 on the regular 11 meters, but that is still not what I am seeking. LC, I have 9 ft of mast below the lower hoop, which is one solid piece, from the top to bottom. Tomorrow I am going to raise it to 30 approx ft, with a wooden insulator between this mast and the 15 addional ft of mast. Meaning I will insulate the Astroplane mast from the lower mast, this is all field studies to get this working the best way possible. I am also securing the coax to the mast directly down the middle of both legs with the loop at 9 ft below the lower hoop as instructed. I will keep you posted as to my progress on the antenna, as I want to get it working properly, so then I can do some detailed testing against my 10-K.Thanks for all the input on this project, JPT.
loosecannon said:
hi JPT,

ok, first, you probably already have this info, but if not; make sure you have the antenna assembled according to the specs in this manual:

http://www.cbtricks.com/ant_manuals/ant_spec_avanti/astro_plane.pdf


as for lowering the SWR, if the SWR isnt about 1.3 to 1 on the CB band, then there is something wrong with the installation. these antennas are made to not need adjustment and will give a very low SWR on the CB band when assembled and installed properly.

yes, you can adjust the SWR by extending or shortening the two lower legs that connect to the hoop at the bottom, but you really shouldnt need to.

the most common problems people encounter with this antenna design is that they dont have a good metal to metal connection from the top mast mounting bracket and the mast, and that the mast is not long enough.

so:

1. make sure you have good metal to metal contact from the upper mast mounting bracket and the mast. (remove all paint from the mast in this area)

2. the mast needs to extend down past the hoop for at least 8.5 feet, and there needs to be good metal to metal contact between all mast sections.
in essence, you need one solid metal pole that goes from the top mast mounting bracket of the antenna all the way down 8.5 feet below the hoop.
i think that equals out to about 16 feet of mast.
the mast is actually part of the radiating system.

3. make sure your coax runs straight down the mast all the way down to 8.5 feet below the hoop. (again, about 16 feet or so)

4. you should secure the hoop to the mast with four lengths of UV resistant rope or monofilament.
this is to keep the mast in the exact center of the hoop.
this is important for two reasons.
A) when the mast gets close to one portion of the hoop and further from the opposite portion, the SWR will fluctuate.

B) if the hoop is allowed to sway in the wind long enough, it will eventually break the aluminum legs that hold it to the antenna.


good luck,
please let us know what you find,
LC
Click to expand...
 
JPT said:
I have started my testing with this antenna, before it goes up in a tree. I am getting good reports locally & have great receive on 11 meters. The SWR's are high on 11 meters 2.2.1 (27.055) & absolutly flat on 29.435. Is there any adjustment (fiberglass hub) on the Astroplane to see if I can get the SWR's lower on 11 meters?
Click to expand...
JPT, this antenna was originally designed for 23 channel radios, but it may have been modified a bit for 40 channels later on by Avanti or others, not sure.

Since your antenna is showing resonance unusually high in band some length would appear missing in the antenna. I don't understand the resonance at 29 mHz you are seeing unless the antenna has been modified somehow by the previous owner or there is a bad connection.

There is no designed tuning for this antenna made by Avanti or other’s commercially that I am aware of. It is designed fixed assembly and probably for the middle of 11 meters.

I do have a suggestion however. Get an OHM's meter and check the continuity of the antenna---fully assembled. Make sure you have continuity at every point from top to bottom in this antenna---when all parts have been assembled. The shorted results you should see may appear wrong to you the way the AP direct feeds, but this is the way it should test---when fully assembled.

However, if you test the coax connector in the hub, shield to center, before you assemble, you should see an open circuit just as you would expect. This all assumes the clip ring buried inside the insulator under the feed point has not be broken in assembly or disassembly of this antenna. The manual should show a warning to this fact and talk about checking continuity. I don’t believe this ring in your antenna is broken or your antenna would fail completely. However, care should be taken in this area.

Mainly check and make sure the two wires in the end adaptor of the top hat assembly are making good contact with each other and that all top element parts connect electrically. For me there is a weak point in the top hat assembly of these kits by some manufactures (maybe all), and this is why checking continuity is well advised.


Again make sure the entire top element is making good contact with the bottom element where they connect in the hub, part A. Also make sure the main support mast makes good contact at the U-bolts and does not protrude above the hub, part A.
 
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