Archive for the ‘Tower’ Category
The tower is now mostly done.
The HF antenna is up, as are the 2m and 70cm yagis. The rotor is installed, and rotates. Mostly. There's a tree in the way of the HF beam, so it can't rotate. I have a guy with a boom truck coming to fix that little issue. I still have coax runs down the tower to make. And install some 3" conduit for the coax entry. And the lightning protection box. And build a rotor protector. Polyphaser wants entirely too much money for theirs.
I had planned to run the conduit today, and mount the box for the lightning protectors., but I got called to go to work instead. Since work pays the bills, and it should be overtime, I'm not complaining. I could use some overtime.
I came up with a simple system for grounding the antenna coax at the bottom of the tower. I'll be working on that a bit more to get it perfected, then I'll post some info and pictures when I actually get to that stage on the tower.
Here's a brief summary of the grounding on my tower as it stands today. It's not perfect, it's not even ideal. It's a major compromise.
I ran a 2" copper strap from one tower leg to a ground rod about 20' away. The strap is buried underground, but only about 4 inches deep. The reason it is so shallow is due to limestone being 6" below grade. The ground rod is a standard 5/8" diameter copper clad rod, 8 feet long, made by Erico. The connection to the tower is a #2 copper wire pigtail that was brazed to the strap with Harris Stay-Silv 5 brazing rod, the wire is then clamped to a tower leg with a bronze ground clamp. I purchased the brazing rod at a local welding supply house. The connection to the ground rod uses a similar pigtail, which is then Cad-Welded to the ground rod using a "One-Shot" purchased from Tessco.
A second ground wire is connected to the tower the same way, then the strap runs to a ground rod, connected with another pigtail. The strap continues on and will eventually be connected to the single point ground for the coax entry panel, which is still a work in progress. There just hasn't been enough time…
My main electrical service is grounded, again via a #2 copper wire, to an existing 8' ground rod at the electrical meter. There I have a 4-way Cad-Weld One Shot, with a #6 wire running to another ground rod for the telco ground, a #6 going to yet another ground rod, and a #2 going to the ground rod mentioned in the previous paragraph, this wire provides the REQUIRED bonding connection between all the services and the tower. It can not be stated enough that this connection is extremely important. Do not skip the bonding step.
The electrical service panel is protected with an LEA whole-house surge protector. The telephone line has secondary protection after it enters the house, just inches from my electrical panel. I'm using Polyphaser IS-MPT-200 protectors. I like these because they are cheap, and they seem to work very well. [edited to add: I've been told these are no longer available] I have a small punch-down block for the phone lines so these work nicely for me. I'm using two because my voice and ADSL come into the house on separate pairs, with a telco provided splitter at the network interface device. All coax will be protected by Polyphaser units, and I'm looking for a suitable rotor protector. Polyphaser makes one, but its rather pricey at around $150, half the price of the entire rotor! ICE also makes one, but I haven't bit the bullet and ordered one yet.
At some point, I'll draw a picture of all of this so it makes more sense.
One additional thing I did was to have my entire re-bar cage welded together, and welded to the anchor bolts for the tower. In the event of a lightning strike, their will be no opportunity for arcing inside the concrete foundation. This also allows the foundation to act as a "Ufer Ground".
There will be more to be said about lightning protection later on.
I'm way behind on updating here.. The tower itself is up.
I home brewed my ginpole using an actual gin pole head I bought on ebay. I added a 10 foot section of 1" galvanized pipe. I didn't buy any brackets, so I used u-bolts to attach it to the tower. Not recommended. And I would much prefer about 12' of 6061-T6 aluminum pipe to the galvanized.
I still don't have my house bracket built. I'm hoping the tower is a bit sturdier once I do. I'm waiting on parts from Cushcraft for the A3S, it sounds like they should be shipping early next week. My mast pipe has arrived. I wanted a seven foot pipe, and the 1 5/8" galvanized pipe I had is very heavy and would be a real pain to get up the tower. I opted for a seven foot piece of Schedule 80 6061-T6 extruded pipe. I found a very reasonable price for it, around $40, and was able to get a couple pieces of brass from the same supplier. More on those in a future post.
So at this point I'm ready to install the rotor and mast, and the 2m beam. The grounding is substantially complete, or as complete as it will get at this time considering that I'm way over my allotted budget for this project. I think it will be "good enough", although it is certainly not ideal, but considering the rock it's hard to get an ideal grounding system installed. I found some major issues with my current grounding that were fixed. I'll post more about the grounding in the future. Hopefully I'll get that house bracket built this weekend.
Some photos this time around.
To build a tower you have to dig a hole. A pretty good sized one. In my case a minimum of 30" square and 48 inches deep. No problem. In normal soil.
I don't live on "normal soil". Our neighborhood is notorious for limestone. Even the electric utility had issues bringing in power due to all the rock in the ground. There's rumors that basements were dug with the help of dynamite. I don't know about that, but what I do know is that I ran into my fair share of limestone. It starts about 6" below the topsoil. And it stops, well, I don't know where it stops. I can't dig that far. But I'm guessing it goes down a long ways since there is a quarry about 1/4 mile east of us.
Needless to say it took me awhile to dig that hole. And in the end I rented a jack hammer to help me get through all that rock.
Just a few of the rocks I dug out.
I ended up making it to 48". I originally wanted to go 60" pretty badly, but after all that rock I'd had enough. That and finding a place to get rid of all that rock.
The Rohn tower book says that the concrete base should be 6" above grade. Or maybe it says 4" above grade. I don't really remember. Many hams leave the concrete several inches below grade, their thought process being that when they take the tower down they can just dump some soil there and plant grass. Good in theory. My concern was water, more specifically, rust. I don't like rusty towers. By keeping the base above grade I'm hoping to avoid any rust on the base of the tower.
So here's the hole, and a 2×6 form to square it up.
We added a welded rebar cage, and the J-bolts for the base plate. And of course, the concrete.
Robert (I didn't catch his call), Jay (KC0AKJ), and Cliffy (KC0RFN) mixed concrete.
I had the easy job, driving the concrete buggy! Best $75 ever spent. Pushing wheelbarrows of concrete uphill would not have been fun.
And here we are, 3500 pounds of concrete mix later.
I'm a bit slow at getting the pictures posted, it's been nearly two weeks since these were taken, so I'm a little bit further along than this. More to come.
Here is the latest on the new tower. So far I have acquired:
- 40' of Rohn 25 tower
- The concrete base plate
- A Rohn heavy duty house bracket (which needed some modifications)
- galvanized concrete anchor bolts
- new Rohn hot-dipped galvanized leg bolts
And so the digging of the foundation has begun. And it's been an uphill battle due to the property being situated on top of solid limestone.
The foundation will be approx 30 inches square, and four to five feet deep, depending on how hard it is to dig the rock once I hit the 4 foot level. You can see behind me next to the house some of the big chunks of rock that I've broken up and pulled out of the hole. Good times. Most of the rock is breaking into baseball sized pieces. There was about six inches of top soil over the rock. This may explain why my lawn dries out so quickly in the summer.
This past weekend I visited KA0ZOZ and acquired a used Cushcraft A3 tri-band beam, a Yaesu G-800SA rotor with 60+ feet of rotor cable, and a Kenwood TS-711A 2m all-mode radio. This has me even more fired up to get the hole dug! I still need to find a 2m yagi to use for SSB, and a bunch of coax. I'm thinking the Cedar Rapids Hamfest next month will be a good place to look.
I have a feeling the worst may be yet to come. I need to find a way to drive a few more ground rods, and trench in some wire between them and the single point ground bus bar at the coax entrance. I also plan to utilize a 'ufer' ground by having the rebar welded into a cage and bonding it to the tower legs.
I now have three 10 foot sections of Rohn 25G tower sitting in my yard. I hope to get started soon getting that thing up in the air.
I still need a 36″ house bracket. Rohn gets $249.00 plus freight for their heavy duty “universal” model which supports both Rohn 25 and 45 (more on that to come). I think I’ll check to see if the local welding shop can make me one. Of course Rohn leaves most of the dimension out of their engineering drawings, but maybe they can figure it out.
I have a "new" (actually refurbished) ATV modulator to mess with. It was donated to me by CadCo systems, and has firmware that allows it to be frequency agile. I hope to get a chance to mess with it soon. I will defiantly have more to say about this.
I'm starting to cook up some plans to operate on Field Day. Our local club didn't seem to have any interest in doing FD, so I'm going planning to do it on my own. So far I have a half dozen or so people that plan to come along.
And in other news, I'm still working on plans for a tower. I think I get some used Rohn 25G that will fit my budget, so I may start digging a hole as early as tomorrow.
Last fall I decided that I would like to start construction of a small tower in spring ’09. I wasn’t sure how many hoops the city would make me jump through, so I got started on that process nice and early.
And I’m glad I did. Turns out there is a height limit on “structures” in the City of Independence of 30 feet or two stories. An antenna, even a roof mounted one, is considered a “structure”. They told me my only hope of erecting a tower was to go before the board of adjustment, and that required paying a fee of $100 just to get them to meet. I tried to explain PRB-1 to the city building official, but he would have none of that.
So I went home, feeling somewhat defeated, but certainly not ready to give up. And not ready to pay $100 either.
It is interesting to note at this point that not only does PRB-1 say that a ham radio operator can build a tower, but there are other rules that could kick in here as well.
As directed by Congress in Section 207 of the Telecommunications Act of 1996, the Federal Communications Commission adopted the Over-the-Air Reception Devices (OTARD) rule concerning governmental and nongovernmental restrictions on viewers’ ability to receive video programming signals from direct broadcast satellites (“DBS”), broadband radio service providers (formerly multichannel multipoint distribution service or MMDS), and television broadcast stations (“TVBS”).
The rule (47 C.F.R. Section 1.4000) has been in effect since October 1996, and it prohibits restrictions that impair the installation, maintenance or use of antennas used to receive video programming. The rule applies to video antennas including direct-to-home satellite dishes that are less than one meter (39.37″) in diameter (or of any size in Alaska), TV antennas, and wireless cable antennas. The rule prohibits most restrictions that: (1) unreasonably delay or prevent installation, maintenance or use; (2) unreasonably increase the cost of installation, maintenance or use; or (3) preclude reception of an acceptable quality signal.
I’m having great difficulty receiving Direct Broadcast Satellite programming from the 129W location due to a tree on my neighbors property, this prevents reception of Cedar Rapids HD locals via Dish Network, my multi-channel provider. I also cannot recieve KIIN-DT, and since that station is technically in the Nielson market serving Independence I would be allowed to install a TV antenna to receive it. Never mind that I can receive KRIN-DT just fine.
So I put together a large packet of information that included a copy PRB-1, the FCC OTARD Fact Sheet, and some background information on Amateur Radio, including a list of local, state, and federal agencies that are served by Hams. I sent these packets to the city council person for my ward, the at-large council person, the city building inspector, the city manager, the mayor, and the city attorney.
On December 1, 2008, I received a letter from the City of Independence giving me permission to install an amateur radio antenna tower in my yard. However, they still require me to obtain a building permit first. I have a sneaking suspicion that they still have something up their sleeve.
More on this subject to come.