Shadetree Mechanic
Delaware Base Station 808
I wish that I was so bored that I had to put up an Astroplane that I had just sitting around collecting dust....
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- Thread starter RT431
- Start date
The Imax is what it replaced. It was about 20ish ft. The AP is at 32'. Always had good performance out of the AP.
LC back in 2009 when I physically made my Old Top One (A/P) with a full 1/4 wave radiator using my Autek VA1 antenna analyzer, I produced an "Antenna Work Sheet" form so I could manually scan my antennas and record the data in the form of a band width chart. Back then I did not know, one day a modern analyzers would do this work in seconds and show results on a computer monitor much less a hand held analyzer device.
Back then, I used a pencil to enter the data and over the years these reports got kind of shabby looking. Sorry! Best I can suggest here is, try using the PDF Zoom feature and get a closer look. Sorry!
Some years later, in 12/14, I made Eznec models experimenting with my Old Top One and making the top element a full 1/4 wavelength in several steps. I can't remember for sure, but I was probably trying to compare, as you've noted above, what was the likely difference, if any, that Eznec might predict for gain, angle, pattern, match, and bandwidth on making the A/P a full 1/4 wavelength.
However, now I notice that some of my models back then showed the mast isolated (ISO) and that suggest to me that Bob was talking to us about isolating this antenna & mast for better results.
I never thought this topic would get this deep into what I found back then. I probably should have kept my mouth shut. Now my memory tends to fail me a bit, so I will have to go back and try and rehash old antenna notes and models I've made that are pertinent to this issue.The old Antenna Work Sheets posted below were easy to recount.
LC, I use to hope that maybe someone would take the time to test some ideas my modeling might tend to show, so thanks for your offer to do just that.
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No mods to this antenna. All parts are factory and followed installation instructions to the letter.
As mentioned, I will have to find my owners manual and look up the specs. I did Google this antenna but all got was the AP with the top hat. By looking at the pic, the top radiator seems to be shorter then the AP without the top hat.
As mentioned, I will have to find my owners manual and look up the specs. I did Google this antenna but all got was the AP with the top hat. By looking at the pic, the top radiator seems to be shorter then the AP without the top hat.
LC, I redid these AstroPlane models comparing a regular A/P with a top hat vs. one with a full 1/4 wave radiator. I wanted to be sure all the other wires were the same for each model an remained the same during the modification. The only wires that changed were the wires for the top element.
The overlay of the patterns show the full 1/4 wave radiator with more gain in the angles from 10 to 30 degrees ,and that is probably to be expected.The pattern shape doesn't look to be much different except for the difference in gain.
I don't think I saw much difference back then or I would have likely been talking a lot more about such a difference. In my test I compared both antenna setups on the same mast setup using the same coax.
Maybe I did some signal reports on this work, I haven't checked that yet.
The overlay of the patterns show the full 1/4 wave radiator with more gain in the angles from 10 to 30 degrees ,and that is probably to be expected.The pattern shape doesn't look to be much different except for the difference in gain.
I don't think I saw much difference back then or I would have likely been talking a lot more about such a difference. In my test I compared both antenna setups on the same mast setup using the same coax.
Maybe I did some signal reports on this work, I haven't checked that yet.
431, I'm not sure what picture your talking about here. The only picture I've ever seen that showed the A/P with a shorter radiator, that did not have a top hat, and was similar to what you may be describing here...was a picture of the A/P as the driven element in the Astro Beam manual. This is where I got the 77.625" dimension for the top element that I mentioned earlier. See PDF file below.
431, you also told us earlier that the A/P is 12" long. If so, and that was to be used as a 1/2 wave driven element on a three element beam...then it would seem to me to be way to long.
Maybe that is why we see this Avanti A/P being shorter in the picture of their beam I posted below.
Avanti added a coaxial 6' foot long dual 59U matching harness for their driven element on their Beam. Maybe they knew the beam would not work right unless they physically made the A/P driven element much shorter than 12' feet. Who knows what kind of feed point impedance the engineers at Avanti found at the feed point on this beam.
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I don't clàim to be àn expert on antennas. I don't anylize every antenna on the market. I really don't care who or how it was made as long as it works for me. If it doesn't, I throw it in the bin and put up another. So far I have 2 antennas in the air that I'm pleased with. And I will play these till I decide it's time for something new.
I've seen the packaging for the AV-100, used to be able to google the image as well but can't seem to find it anymore. I believe it is the same as the center part of the AV-150 Astro Beam.
That does seem to be a much larger difference than what I saw when I was playing with the models... I wouldn't expect to see that much of a difference just because of a cap hap... I don't have any of my old AP models, I guess I will have to remake said model again sometime...
The DB
DB, I was also a bit surprised at the difference in gain shown above.
When I tried comparing some of my older models earlier for Loosecannon, I found differences between the wires and segments among the models I checked. So, I took an old A/P model that showed a good match and produced a pattern that was very similar to a vertical CF 1/2 wave dipole at 36' feet. I used that model to modify a 2nd model, with a full 1/4 wave radiator at resonance, in order to compare these two ideas.
I've already said many times, when I compare these 2 different design ideas in my real world testing...I saw little to no difference just using my radio. Back in the day, lots of folks seemed to disagree with that idea completely...some suggesting that is impossible, saying the full 1/4 wave radiator will perform much better.
DB, maybe you could do the models for Loosecannon's sake, just in case I've made some gross error that might mislead him and waste his time installing his A/P.
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I had an AP back in the day and I loved it. Not sure if it was the best antenna ever but it did very well for me in comparison to many other antennas that came later.
Anyone have any experience with the clones?
Anyone have any experience with the clones?
Wow, that brings back memories. In the early 70's I replaced my A/S "Super Mag" with the AP and I recall that I (and the fellas I talked with) perceived a positive difference over the A/S. In the 90's I bought an AP clone and other than being very cheaply made (very thin aluminum) it worked fine until it got bent/twisted up during a hurricane.
Of course, different QTH altogether from the 70's so no real way to compare. And I just had a memory flash of buying an original AP about 10 years ago...I think I'll go forage around in the garage to see if I kept it when we moved.
I let a friend have my original AP after I got a Shakespeare Big Stik up at 60 ft. He got a lot of good use out of it but I did miss seeing the AP on my roof. Don't know why but it did look interesting vs. the ground planes everyone else had.
i would like to thank you Marconi and the DB for the work you have put in on this stuff over the years, and for me personally.
It looks as though there are some small gains to be had when using an 89" vertical top element over the cap hat version.
i suppose i will try this way first, and use it this way for a while to get used to it, and maybe in a year or so change it back to cap hat style.
does anyone know the thread pitch of the top one where the top element connects?
i remember those threads being finicky.
I don't want to cut down my one stainless steel 102" whip for this, so im going to have to find some aluminum i can sleeve.
LC
It looks as though there are some small gains to be had when using an 89" vertical top element over the cap hat version.
i suppose i will try this way first, and use it this way for a while to get used to it, and maybe in a year or so change it back to cap hat style.
does anyone know the thread pitch of the top one where the top element connects?
i remember those threads being finicky.
I don't want to cut down my one stainless steel 102" whip for this, so im going to have to find some aluminum i can sleeve.
LC
BTW are you using a Top One or a real A/P?
LC, consider making this full 1/4 wave radiator using an additional length of tubing that is attached to the top of the shortened stock radiator to get to about 89" inches overall.
I used a tube of aluminum from the tip of my Sigma4 antenna. It was 45"L x 1/2"D. With about 2" inches of overlap for the stainless hose clamps. this is got me the length I need to see a good match at resonance in the middle of the 40 channel CB range.
This will allow for simple tuning as necessary, without cutting up a SS whip, and you don't have to worry about fixing parts that screw together just for a comparison test.
You can always make it look pretty later...after you've tested the idea.
Good luck and keep us posted.