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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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  #41 (permalink)  
Old 08-03-2017, 2:20 PM
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Originally Posted by cmdrwill View Post
I would think on getting a better aka commercial antenna than the Diamond Comet junk The Diamond will fail in the winds, and only have a 19 gauge steel wire with piss poor copper plating for an element.. not to mention the very thin fiber housing.

Is there one that you would recommend that has similar gain? Im not familiar with any commercial equipment. A wide band version would be nice so that i could still use MURS or something similar when my kids are out and about on the property. We are currently using some Baofeng uv-5r programmed with the FRS GMRS bands in them. Even at 5 watts, they won't reach all of our property. It would be nice to get a commercial wide band antenna that could keep SWR down in the higher frequencies for that application. But then again, with that much gain, i don't think it would make a difference when they are only 1/2 mile away. I have a feeling they would still be under the radiation pattern.
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  #42 (permalink)  
Old 08-03-2017, 2:30 PM
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Originally Posted by RFI-EMI-GUY View Post
Go for the height. Rohn is probably specifying to the force applied directly at the mounting point measured above ground. The antenna itself, has a survival rating. complicating this, is that the feedline has a wind load, but it is distributed over the height of the tower. It will probably be negligible in your situation. But if it worries you, the feedline should be tied close to one of the tower legs which will reduce its effect somewhat.

Back during Hurricane Andrew I lived 2000 feet from Biscayne Bay in an area that received some very high wind velocities I think 140 MPH (edit 115 gusting to 164 MPH at the nearby NHC building) . Trees were toppled, but buildings spared. I had a 9 dBd fiberglass Decibel Products UHF base station antenna, some 17 feet long atop a 2 inch galvanized water pipe that was two sections totaling 20 feet long, buried in a bit of concrete and anchored to the gable of the house. Next to it, a 1 1/2 inch TV mast 20 feet tall with a small RV television antenna (wing shaped) and rotator similarly fastened to the gable . After the hurricane the base station antenna was intact, the gable mount attachment (a weak point) merely pulled away. The TV antenna was another story, it was a mangled mess, the mast bent over into the neighbors yard.

My point being, that a cylinder antenna might impart less force than an irregular antenna like a yagi.
After speaking with someone earlier today, i was told that they don't even measure wind load for vertical antennas because its so low. Turns out i was wrong earlier and the wind load is actually 0.5026 ft2.
You are correct on the fact that a cylinder imparts less force. WAY less apparently! I grew up in south Florida myself and was in miami at the time of hurricane Andrew. I remember watching out the window as trees were ripped out of the ground and thrown. Then later saw those same trees floating down the street. We drove thru homestead seeing if we could be of any help as soon as it was over. Talk about a disaster! Anyways, it sounds like this is going to be similar to your UHF base station antenna. This antenna is 17.2" long. I was previously looking at the X700 that is 24 feet at 13 dbi at uhf and 9.3 on vhf. I think that one may be a little overkill and the Diamond rep actually recommended the X500 heavy duty because of wind.
Thank you for the info. It has helped me out a lot!
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  #43 (permalink)  
Old 08-03-2017, 4:22 PM
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I hope you do not really believe those so-called gain numbers. And will not cover the MURS and Ham bands and GMRS you mention.
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Old 08-03-2017, 5:08 PM
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I don't believe that they are 100% accurate. I look at them like published velocities of ammunition. They are never correct unless in specific conditions and with specific equipment. However, i do use them as a baseline of sorts. An antenna that is published as having only 3 DBI is most likely still going to have less gain as one publishing a gain of 13 dbi when looking at reputable companies. Do i believe that they are really going to get the published 13? No, but i do believe that it will still be higher than the one listed as only 3. I have no idea of how to actually measure gain myself. That is something that is way over my head and most likely most end users. But, i am still looking at the published numbers and reading as many reviews as i can. That and other peoples opinions are the only thing i have to go off of.
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Old 08-03-2017, 5:17 PM
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Originally Posted by cmdrwill View Post
I hope you do not really believe those so-called gain numbers. And will not cover the MURS and Ham bands and GMRS you mention.
A commercial antenna should cover those frequencies just fine. At least from my knowledge. I have one now that is a roll up Jpole in the attic that is tuned for optimal resonance on frequencies 151.820 - 154.600 and 462.575 - 467.725. I could always just move this outside on a mast and use that with the portable.
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  #46 (permalink)  
Old 08-03-2017, 5:55 PM
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Commercial antennas are rated in dBd because that is referenced to a dipole and NIST has methods to certify dipole gain.

Ham antennas are in dBi which sounds better than same antenna in dBd because the number is 2.15 dB greater.

dBi is referenced to isotropic . Not much in the physical world, apart from perhaps the sun is an isotropic radiator. Microwave dish antennas are referenced in dBi because their pattern gain can be determined from a power concentrated in a section of a sphere.

Then you have the bandwidth dilemma. It is a challenge to produce a wideband antenna with gain. Colinear antennas might be spec'd as wideband but you experience pattern tilt at one end of the band versus the other. As a consumer, You pretty much have to hope the VSWR is ok and hope for the best.
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  #47 (permalink)  
Old 08-03-2017, 6:41 PM
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I never knew that commercial antennas were rated in dBd. Thank you for sharing that. Do you have any pointers in how to select a good antenna for a base station for long range simplex? Im not interested in a directional antenna just yet. I may add one in the future. I only knew that dBi was isotropic, but thats about where my knowledge ends on that one. Lol

Thanks again, more to read up on! I have been playing with Radio Mobile Online This has given me a better understanding of what to hopefully expect. At least its fun to play around with. It is showing that if i was to go up the additional 60 feet to take my current plans to 100, that i wouldn't really gain a whole lot in the direction that I'm most interested in. It will give me more coverage to the South East and not really a whole lot. So it looks like 40 feet will get me what i need. If anyone is looking for a way to spend half a day playing, get on there and start messing around with stuff. Its a lot of fun!
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Old 08-06-2017, 9:34 PM
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Quick update. We were unable to get our schedules to match up the other day and get the tower moved. We did however get it moved today. I may update with some pictures tomorrow. I will be getting concrete soon and i am also looking into a different tilting base for the Rohn 25. I put in a call to NormsFab and am waiting a call back. I still need to pick up the 1/2"x12" bolts for the concrete. I did go ahead and pick up an 8' grounding rod and hardware. I still need to get the copper grounding wire that will go from the tower to the grounding rod. I may just go take some off of the power pole i planned on using earlier. I am still far from having everything i need. I still need to order a polyphase, coax, etc. It will still be a while, but its moving along.
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  #49 (permalink)  
Old 08-15-2017, 1:38 PM
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I have run into some health issues from combat injuries i sustained 9 years ago. So, for now, this project has stalled. I will continue once i get things back on line. Thanks to everyone for all your help.
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  #50 (permalink)  
Old Today, 11:11 AM
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Ok, so I'm back at it again.
Quick update. About 2 weeks ago i ended up going blind in my right eye for a short period of time, about 4 minutes. It was long enough to scare the crap out of me and send me to the ER. To make a long story short, Due to my age, health, etc. The Dr. believes that it is some how related to some old brain injuries i sustained in 2008. Needless to say, i took some down time to rest and see how things will go. So far, so good. So that leads us back to this project.

I have already dug the hole for the concrete to be poured. First hiccup that i have run into is that the local concrete companies will only deliver loads of 3 yards or larger. So, this leaves me with buying LOTS of bags and mixing by hand in a wheel barrow. We are expected to start getting some really bad weather tomorrow and later this week, so i don't want to start concrete today. Once the bad weather passes, i will go ahead and start mixing and pouring concrete.

In the mean time i am going to do some tower maintenance. I am trying to decide between priming and painting the tower, or re-spraying with cold galvanize. I think the prime and paint will look better, but what holds up longer?
I know i need to get a primer and paint that is compatible with galvanized steel. In fact after speaking with ROHN today i was told that it may not even matter because of the age of the tower. It is believed that the tower may have aged to the point that the Zinc is now neutralized. So i was told that i could use a primer, preferably an acid etch primer, and a good paint. I looked at the local tractor supply at some of their farm paints used to paint tractors and galvanized steel feed bins and the like. I may go with something like that.

So, for now, i am going to locate some primer and paint and get this thing ready for concrete.
Any recommendations on brand or type of paint from anyone?

Thanks again everyone, sorry it stalled there for a while.

Last edited by 19dsniper; Today at 11:16 AM.. Reason: spellin !
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  #51 (permalink)  
Old Today, 12:50 PM
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I've never seen any paint or primer that will last over galvanized, even if its rated for that. I've had multi million $$ satellite antennas where the paint peels off in a few years and they were properly treated and painted over galvanize.

Cold galv is ok for touch ups but I would not cover an entire object with it.
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Quote:
Originally Posted by 19dsniper View Post
Ok, so I'm back at it again.
Quick update. About 2 weeks ago i ended up going blind in my right eye for a short period of time, about 4 minutes. It was long enough to scare the crap out of me and send me to the ER. To make a long story short, Due to my age, health, etc. The Dr. believes that it is some how related to some old brain injuries i sustained in 2008. Needless to say, i took some down time to rest and see how things will go. So far, so good. So that leads us back to this project.

I have already dug the hole for the concrete to be poured. First hiccup that i have run into is that the local concrete companies will only deliver loads of 3 yards or larger. So, this leaves me with buying LOTS of bags and mixing by hand in a wheel barrow. We are expected to start getting some really bad weather tomorrow and later this week, so i don't want to start concrete today. Once the bad weather passes, i will go ahead and start mixing and pouring concrete.

In the mean time i am going to do some tower maintenance. I am trying to decide between priming and painting the tower, or re-spraying with cold galvanize. I think the prime and paint will look better, but what holds up longer?
I know i need to get a primer and paint that is compatible with galvanized steel. In fact after speaking with ROHN today i was told that it may not even matter because of the age of the tower. It is believed that the tower may have aged to the point that the Zinc is now neutralized. So i was told that i could use a primer, preferably an acid etch primer, and a good paint. I looked at the local tractor supply at some of their farm paints used to paint tractors and galvanized steel feed bins and the like. I may go with something like that.

So, for now, i am going to locate some primer and paint and get this thing ready for concrete.
Any recommendations on brand or type of paint from anyone?

Thanks again everyone, sorry it stalled there for a while.
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  #52 (permalink)  
Old Today, 1:28 PM
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Any recommendation on what should be used on an older tower? Or should i just leave it alone?

I have surface rust on some sections. It was laying down on some pallets for the last few years. I have looked it over and even used a borescope to check inside as far as it will reach. Its not long enough to run past 5 feet (longest stretch from each end of a single section) but so far everything inside looks good. Outside has a few spots of some surface rust in a few small spots. I was going to get it cleaned up with a wire wheel with my hand drill. Then i was going to prep and seal it to prevent any further spreading. I spoke with ROHN about it and of corse they recommended a "Blended Vinyl Acrylic Emulsion" after prepping the surface with a mix of "copper chloride/copper Nitrate/ Sal Ammoniac, Muriatic acid" and then a rinse and dry before applying the Blended Vinyl.

I was hoping there was a much simpler solution. This is what prompted my call to them this morning and the comment made by them that a tower of its age was probably already unprotected due to the age of the zinc and it being "neutralized over time". I told them i was hoping that there was product that was available local for me to purchase as their specialty Blended Vinyl stuff was extremely expensive and only available in certain areas, which he verified it was not available here. He then recommended that i go speak with someone at either Sherman Williams or Rustoleum and to pick a product that is rated for outdoors, and does not contain aluminum.

After speaking with Rustoleum they recommended that i use a product know as "Aluminum Primer, 8781" that is used on aluminum or galvanized items. Then a top coat of whichever color i want.

Maybe i will use the Zinc Cold Galvanizing Spray on the problem areas and leave the rest alone. I was just hoping to ward off any future problems, and i will admit that i am a fiddler and want to mess around with this stuff while its on the ground and hasn't been installed yet. If there is something i can do to improve its longevity before it goes up, i would like to do it.

Thanks again PRCGUY!
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