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Message |
    
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1241
Registered: 9-2004
| | Posted on Tuesday, February 28, 2006 - 7:02 pm: | 
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hi folks,
im going back and forth between buying a new antenna or putting my top one (which im very happy with) back up high in the air.
about 45' to the feedpoint.
im pretty much decided that im going to keep the top one for now, until i have more room to really benefit from the IMAX or maco V5/8. (cant go very high with them here)
so my question is: what does the radiation pattern of the Top One (Astroplane) look like as it relates to sending some of the signal straight down towards the earth?
does the antenna do this?
does the hoop keep the signal from radiating downward?
is there a way to use guy wires on the mast at a certain length below the hoop to act as a sort of counterpoise?
would the length of these "radials" matter?
does this antenna exibhit similar characteristics to other antennas when it comes to reducing TVI by raising the antenna?
i am not having TVI issues at the moment; i do overload the TV's in my house when using rabbit ears, and mostly on 2, 3, 5.
i want to be able to run power here without worrying whether the neighbors can hear every word i say whether they like it or not.
i want to be a good neighbor and be able to run about 400 watts.
i use LMR400 coax.
any suggestions or answers?
thanks in advance,
matt |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1244
Registered: 9-2004
| | Posted on Tuesday, February 28, 2006 - 11:07 pm: |
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i also want to use a choke balun at the feedpoint, but the design of this particular antenna doesnt make this too easy.
with this antenna; do i have to put it below the hoop?
any certain length below?
hope someone can help me with these. i realize im asking somewhat obscure questions here.
thanks,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 617
Registered: 11-2001
| | Posted on Wednesday, March 01, 2006 - 12:49 am: |
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Kid this is my take on the AP. It is basically up side down. The voltage node of the antenna is at the bottom hoop and thus it is susceptable to anything near it or within at least 9' or so. I would not try reflective guys and if you do the docs suggest insulators right at the mast or high SWR may occur. It also suggest that the mast be at least 12' long and metallic although I believe that if the mast was non-conductive that the antenna would then use the shield of the decending coax to aid in tuning of this antenna.
The AP is very light and the way I have seen it respond to high wind it seems very stable and well balanced even so with the antenna pretty much evenly balanced around the mounting point at the hub.
I have placed my Field Strength Meter right under this antenna and due to its very long and smooth transition of AC to RF with a 1/4 wave feeder feeding the voltage node at the bottom hoop and working against the feed line/mast as the ground, it is remarkably well decoupled and shows no, ZERO, RF on the feed line even with the FS device right at the mast and coax and removed by at least 10' feet below the bottom hoop or more. This may account for this ones reported good nature regarding the lack of TVI and being a very well matched radiator. I have no idea what the radiated pattern of this antenna is, except what the advertising shows for it. But, I believe it is an antenna that is phycically longer than a 1/2 wavelength, and electrically is brought to resonance at something on the order of 3/4 wavelength like most of the longer elements will do. How else can this or any antenna be resonant if it does not electrically appear as 3 -1/4 wave lengths long. All other lengths longer than a 1/4 wavelength are not even close to being resonant. Remember only a 1/4 wave radiator or any uneven multiple will show a natural match at resonance. This includes a end fed or OCF half wave radiator too. The matchers in these longer devices are only adding inductance to offset an excess of capacative reactance by the radiators being to long to show resonance. That is why I claim all these longer antennas are the same except the way they are matched out that brings the capacative loaded radiator into resonance. That is not to say that there may be other difference due to different lengths here, but I will not go into that issue, because I have not a good agrument for that aspect, but I am working on it.
That being the case the AP antenna will exhibit a very low takeoff angle and I blieve due to the nearly 50% of the radiator being in the horizontal field this antenna also responds very well to horizontal signals during skip periods and even to horizontal patterns during local transmissions. This may well be substaintated by reports that it does not work quite as well as some others that are purely vertical, like the A99 and Imax and others, when working locally. But given good DX conditions this little booger should shine big time for you.
I also believe if you get it up high, you will also be somewhat surprised at how well it does up high. I know it has a bad reputation of only working well down low, and that maybe true also, but you get it a little height and watch out when DX comes back.
Even the modern knockoffs seem to work very well and most I have seen are sturdy enough if you change all the hardware to Stainless including the U-bolts in the hub.
My opinion of the Astro Plane a great little antenna that holds up pretty well if you change the hardware. |
Tech833
Moderator
Username: Tech833
Post Number: 1237
Registered: 8-2002
| | Posted on Wednesday, March 01, 2006 - 1:04 am: |
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The Top One is sort of an 'upside down' 1/4 wave ground plane antenna so the current node is in the air and the voltage node is toward the ground. The short answer is very little RF goes groundward, almost all goes up and out. |
Tech833
Moderator
Username: Tech833
Post Number: 1238
Registered: 8-2002
| | Posted on Wednesday, March 01, 2006 - 9:54 am: |
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Marconi's posts always get approved before mine.... He must be quicker on the keyboard then me.
Using guy wires attached a few feet below the hoop won't hurt a thing, although the original AP instructions mention it is a good idea to insulate the wires right below the antenna. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1254
Registered: 7-2004
| | Posted on Wednesday, March 01, 2006 - 11:08 am: |
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I had no trouble with TVI/RFI when i had a
Top One up for a few months. My house is
26 ft. to the peak. Had Top One up 5 ft.
over peak. 31 ft to hoop.
I did not test it while running 400 watts.
Only 100 watts max. No TVI or RFI problems.
Now the Imax 2000 was a different story and a nightmare for me. My neighbors are 25ft and 35ft away from antenna. |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 860
Registered: 6-2003
| | Posted on Wednesday, March 01, 2006 - 11:50 am: |
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Wow, Marconi, that was a good lesson on the AP. I like that antenna. It's a good SW antenna too!
Mikefromms |
Bruce
Senior Member
Username: Bruce
Post Number: 3601
Registered: 9-2003
| | Posted on Wednesday, March 01, 2006 - 1:28 pm: |
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After mine was flattened around the mounting pole by a hurricane 100+ MPH winds in 2004 it worked great aorund corners ......
All kidding aside before that .....
I do agree this is one fine small antenna but the hardware is poor at best |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1246
Registered: 9-2004
| | Posted on Wednesday, March 01, 2006 - 4:52 pm: |
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thanks to all for responding.
always glad to hear that the guru's have the same ideas i do.
i definitely know about the hardware!
in the article i did on this antenna, titled: "top one at 44' to the tip",
i told anyone reading it to upgrade their hardware before putting one in the air.
i used 1/4 inch SS hardware and nylock nuts.
so here's the new plan. i lowered my antenna right before a 70mph windstorm came through town, because i noticed that it could have fallen on the neighbors new gazeebo.
now im ready to put the antenna back up, but the gazeebo is staying, so the antenna is moving.
im going to mount it on a 30' push up pole right in the center of the roof.
i already have eye bolts and turnbuckles in all the right places for this.
this time i will still use the dacron rope, but i will guy the antenna in four directions from the TOP OF THE ANTENNA!
i want to take advantage of the design of this antenna and increase the safety factor.
i will attatch the guy ropes to the U-bolt at the top of the antenna, and then one more set on the first guy ring below the hoop.
my only concern is that this may create too much stress on the top vertical radiator.
i dont think it will matter, but im not sure yet.
i still want to use the choke balun.
is there a certain distance below the hoop that would do the most good?
if i add a 5 foot mast to the 30 foot pushup pole on my 15' roof; it will put the top radials right at about 54'.
any advantage to this over 49'?
thanks for any suggestions,
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1239
Registered: 8-2002
| | Posted on Thursday, March 02, 2006 - 1:02 am: |
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Hi Matt.
That dacron rope will soak up some water when it rains, and it will raise the SWR on your Top One.
A choke balun will do nothing with a Top One.
The difference between 49 and 54 feet using a Top One will be exactly zero. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1250
Registered: 9-2004
| | Posted on Thursday, March 02, 2006 - 10:56 pm: |
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thank you paul!
since i live in las vegas, and it is windy here A LOT more than it is wet; do you really think this will be much of a problem?
im asking in all seriousness because if you say that it will cause SWR problems; i wont do it!
sure would be nice to have the antenna guyed at the top.
can you explain to me (without hurting my brain too much) why a choke balun will do nothing with this particular antenna?
could this be yet another advantage to this design?
the only reason i even thought that five feet would make even a slight difference, is that 54'
is 3/2 wavelengths above ground, (unless im mistaken about this too!) and i thought that having the radidating elements right at that height might make some sort of positive difference.
thanks very much for taking the time to explain this stuff to me.
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1240
Registered: 8-2002
| | Posted on Friday, March 03, 2006 - 11:22 am: |
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If your ropes are not wet, they will have no effect on the antenna.
A choke balun will do nothing because there is no stray current below the antenna, it is all on the top of the antenna (the opposite side of your coax).
The height is not some magic tuning strategy, especially with this antenna. Don't spend any more brain cells on it. Just slap it up at whatever height you get and go like crazy! |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1252
Registered: 9-2004
| | Posted on Saturday, March 04, 2006 - 8:28 pm: |
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thanks paul!
you just gave me an extra 19' of coax to work with!
just have to buy the push up pole, then i'll be in business.
nice not to have to build the choke!
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1247
Registered: 8-2002
| | Posted on Sunday, March 05, 2006 - 4:42 pm: |
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This is a great antenna design. It work well, and holds up to weather. It may not lay out the same huge pattern as an Imax 2000 will at 60 feet up, but if you do not have a lot of height to work with, it will outperform the Imax in many ways since the Imax does not work well low to the ground. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1258
Registered: 9-2004
| | Posted on Sunday, March 05, 2006 - 9:08 pm: |
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i am certainly a huge proponent of this antenna.
with the way houses are built right next to eachother in the urban areas these days; this antenna is the answer to a lot of city CB'ers woes.
one more question paul, (for now!)
so far, my plan is to use a 30' push up pole and to put a 5 foot mast on top of the push up pole.
this will put the top guy ring of the push up pole just below the middle mast support. (the one that holds the antenna sections a certain distance apart).
the lower vertical elements wont actually touch the guy ring, but will it cause a problem being there?
should i remove it?
i think it was you that told me that the distance between the elements as opposed to the mast, makes a difference in the tuning of the antenna?
am i off base here?
i'd like to leave the guy ring there if i can.
does this question even make sense? sometimes i cant tell.
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1250
Registered: 8-2002
| | Posted on Monday, March 06, 2006 - 10:31 am: |
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The guy ring will not affect anything. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1267
Registered: 9-2004
| | Posted on Monday, March 06, 2006 - 9:52 pm: |
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alright!
i really appreciate you sticking with me on my quest for assurance on my new install.
one last question, i promise!!!
is there a non conductive guy rope that you know of that wont soak up water?
im not opposed to using something that wasnt necessarily intended for this pupose; as long as its tensile strength is up to par.
thanks immensely for you invaluable input,
matt |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 82
Registered: 8-2005
| | Posted on Tuesday, March 07, 2006 - 2:52 am: |
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Im going to doing a similar setup using aluminum masting tubes to hold up my Maco v5/8, I am going to use kevlar guy wire that has dacron over it for UV protection. I has no stretch and will hold 150 LBS. continous Breaks at 770 LBS. I know where you can get 500 feet for 60 dollars. |
Tech833
Moderator
Username: Tech833
Post Number: 1254
Registered: 8-2002
| | Posted on Tuesday, March 07, 2006 - 10:35 am: |
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Kid, Do a web search for Phillystrand (also called Phillystran). That is what professional towers use for non-metallic guy cables. Will not break, ever. |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 84
Registered: 8-2005
| | Posted on Tuesday, March 07, 2006 - 5:55 pm: |
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Phillystran is Kevlar, you can buy it up to 1/2 inch for supporting heavy/tall towers. Probably overkill for a small antenna system. Im using 1/8th inch to support my 34 foot aluminum antenna mast. Im guying it at three sections also since I will have two antennas on it. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1269
Registered: 7-2004
| | Posted on Tuesday, March 07, 2006 - 7:09 pm: |
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Phillystrand is similar to Kevlar,but, different.
I use 1/8" Kevlar (tripled).
Not sure how it will hold up yet. Only been
on since Oct of 2005. |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 86
Registered: 8-2005
| | Posted on Tuesday, March 07, 2006 - 7:42 pm: |
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Are you sure? I was just on the manufacturers website and they said it was Kevlar. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1271
Registered: 9-2004
| | Posted on Tuesday, March 07, 2006 - 9:49 pm: |
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thanks yet again paul!
you definitely da man!
matt |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1270
Registered: 7-2004
| | Posted on Tuesday, March 07, 2006 - 10:09 pm: |
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The site i pulled up said, Phillystrand
was similar to Kevlar. Below is part of the
website......................................
Phillystran is a non-conducting guy wire material made out of aramid fiber and is like Kevlar - strong and lightweight. It comes in different diameters and strengths. |
Tech833
Moderator
Username: Tech833
Post Number: 1257
Registered: 8-2002
| | Posted on Tuesday, March 07, 2006 - 10:15 pm: |
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Phillystrand will hold up for many, many years. I have a set of 170 foot guyed towers for an AM station that use Phillystrand from top to bottom and they have been up for over 30 years. The Phillystrand still looks brand new and has not stretched one inch. Kevlar is not stable enough to stand up to UV rays and outdoor extremes and will fail fairly quickly. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1271
Registered: 7-2004
| | Posted on Tuesday, March 07, 2006 - 10:30 pm: |
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Since my guy wires are not really necessary
in my installation. I'd like to see about
how long the Kevlar with Dacron outer coating will last. Then, i'll replace them with Phillystrand type guy down the road. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1272
Registered: 9-2004
| | Posted on Tuesday, March 07, 2006 - 10:33 pm: |
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wow!
.45 a foot!
and thats the smallest size i could find.
looks to me like Texas Towers is the only place to buy from.
am i wrong?
unless i can find some cheaper; i dont think i'll be using this.
anyone else using this stuff?
matt |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 88
Registered: 8-2005
| | Posted on Wednesday, March 08, 2006 - 1:28 am: |
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Here is what Texas Towers website said about Phillstran, "Phillystran is an electrically transparent nonmetallic guy cable which offers complete guy line isolation, eliminating the need for insulators. It's constructed of KevlarŪ fiber, covered with an extruded copolymer jacket which provides full UV protection." |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1272
Registered: 7-2004
| | Posted on Wednesday, March 08, 2006 - 10:19 am: |
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After doing more reading on other sites:
This article says:::Texas Towers is the only place that sells Phillystran. Phillystran consists of a Kevlar fiber core and a PVC jacket.
I haven't looked on the Texas tower site yet.
The Kevlar rope i'm using DID NOT come from
Texas Towers, so, i'm assuming it's different. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1273
Registered: 7-2004
| | Posted on Wednesday, March 08, 2006 - 10:35 am: |
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After looking at Texas Towers Phillystran
cable. It is not like what i use.
It looks to be a much, much better cable than the
Kevlar type i'm using. |
Mrclean
Junior Member
Username: Mrclean
Post Number: 32
Registered: 12-2003
| | Posted on Tuesday, March 28, 2006 - 9:46 pm: |
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I use dacron rope to hold a Pogo Stick at 36 ft on a push up mast. Using the small stuff. Held up fine in 70 mile an hour winds. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1300
Registered: 7-2004
| | Posted on Wednesday, March 29, 2006 - 11:59 am: |
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I think the point here is when guying a
tower or mast for safety it's best to
go with something that will stand-up to
years and years of weather conditions. Some types will break-down in a short period of time of
being exposed to weather conditions.
In my situation, my guy wires are not really
needed, so, if they fail, no big deal. I want
to see how long the Kelvar rope with Dacron
outer cover will actually last here in PA.
A place will a hotter climate it probably
would not last as long.
But, if your guys wires are needed, not a wise
thing to do. |
Tech833
Moderator
Username: Tech833
Post Number: 1294
Registered: 8-2002
| | Posted on Thursday, March 30, 2006 - 10:32 am: |
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MrClean,
RW is right, the concern here is not whether the guys will hold up to 70 MPH winds today, the question is whill they hold up after being subjected to sun and elements over time. Corrosive air (in cities and near industrial areas) and the sun are flexible materials' worst enemies.
In a case where a structure could be free standing, the concern shifts to what happens when ONE guy fails and the rest try to pull the structure down. The upwind guy will be the one that fails, so then your structure has wind pushing and the remaining guys pulling in the same direction. Ouch. |
