Go to a local electrical supply house. You can get thick wall aluminum pipe with NPT threads on each end and in 10' lengths. If the supply house won't sell to you retail, you can find a local electrical contractor and order it through them. This is thick wall pipe, not tubing. You probably should guy it.

I have been thinking (oh no!) of making a couple of dipoles. One for 10 meters and one for 6. I want to mount them vertical and was wondering if I could use tubing for the elements with an insulator at the middle and the coax running up inside the lower element. Below the lower element I would coil the coax to form a choke.
 The idea for running the coax inside the tubing is so I don't have to run the coax off at a right angle before coming down so it doesn't interfere with the lower element.
 I'm thinking that I could use some sch.80 pvc on the lower element for a mast.
 I can get some aluminum tubing for the elements. Probably use 1/2 to 3/4" diameter. This will be thick wall tubing. Actually this tubing is probably better called pipe. What is the criteria for calling tubing: tubing or pipe? Is it the wall thickness? The aluminum pipe I get is from an electrical supply shop. 10' lengths with NPT threads on each end. Sturdy stuff.

I once used a magnet mount antenna on a second floor balcony using window screen for the ground plane. I got the metal variety (fiberglass is very common but won't conduct). Layed it on the balcony floor, layed some outdoor carpet over it. Cut a hole for the antenna base to contact it directly and it worked fine (well, there is only so much you can expect from such a setup). I only used it on 10 meters on HF.

The design was for 148 mhz and it actually came out resonant (according to my MFJ 259b) at about 143 mhz. Probably the trouble was my using insulated wire. The original design used a fiberglass boom and I was using a 1' diameter aluminum conduit. The spreaders were 1/4" wood dowel. The aluminum boom was not grounded when I was testing. The feedline was RG8/X, and was connected directly to the driven element. The feedline came off the driven element at a 90* angle and did not run along the boom to the mast. There was no mast at the time, the antenna was hung on 2 wooden boards about 10' off a concrete driveway. I used a wooden ladder to work on it. There were no large metal objects nearby. My friend's wood frame garage with wood clapboards was about 8' from the antenna and his wood frame house with wood clapboards was about 14' the other way.
 I guess I need to get a couple of antenna books and study a bit. I'll try it again but I'm a bit busy with my truck resto right now. Its cold outside here in Minnesota and the truck fills up the garage. I appreciate all the help from you guys.

So, I go to a web site and get some dimensions for the quad antenna. They are (of course) nowhere near correct. 3 hours of work tossed in the trash heap. Is there a law that says all antenna dimensions freely shared must be a minimum of 3 mhz off?
 A friend tells me he'll help with the antenna. He's never done something like that and thought it would be interesting. I had a questionable tire on the front of the truck so I spend $140 that I really can't spare so I can travel the 100 miles without worry. After 3 hours of work I realize that these dimensions are so far off, I will have to trim every element and every spreader by so much that the spacing can't possibly any good anymore.
 God, I love this hobby!
 Anyone know where I can find some realistic dimensions for a 2 meter quad?

Well, it seems we have found a flaw in all those engineering books (just kidding).
 These antennas will be mounted with the booms parallel to each other, pointed in the same direction.
 I was wondering about having one vertical polarization and the other horizontal because I won't know what the other station will have for polarization and thought I might be able to cover both bases this way. I am going to be getting an all mode 2 meter and wanted to get a beam up. I have no experience with 2 meter ssb. Do you guys think its worth it to have circular polarization? I don't have any plans to work satellites. Would I generally be better off to just have them both one or the other? If so, which polarization would you suggest? I am thinking vertical would be the way to go as most of the 2 meter antennas I see locally are vertical. Also, how far apart? Is the distance apart measured from the booms or the nearest element? Seems to me that the measurement should be from the center of the antenna.

I am planning to build 2 5-element quad 2 meter antennas and mount then on opposite sides of my mast. I am wondering about how to connect them. Should they be in phase with each other? Can I turn one 90 degrees so one is horizontally polarized and one vertically polarized? How far apart should they be? Need input.

There's a great Idea! Leave the band so the CBer's can have it.
 Seems to me, the only way to get rid of them is to track them down and shut them down. You know, enforcement of the law. Strange idea I admit. I also realize it will be an ongoing operation. There are a lot of outbanders out there. But you know this administration: don't enforce the laws, just make new ones.
 I don't, for even a moment, believe these lack of money excuses. Given the equipment at their disposal, I just can't understand why the FCC refuses to do anything.
 They try to restrict the selling of modifiable radios instead of shutting down those who are breaking the law. Don't go after the people breaking the law, go after the radios. Problem is; any competent tech can modify any radio to go anywhere they want it to go. If someone wants to use a frequency, they can put a radio on it. ANY radio. You will never stop the problem by restricting the selling of radios. they are too easy to build. You need to enforce the law and track down the perpetrators.
 If our poor, poverty stricken government needs a hand, how about some of these T-hunting clubs helping out? Seems a worthy cause to help clean up some of our bands.
 Or am I just full of it? (nah, couldn't be!)

It seems that the FCC is too busy watching ebay for 10 meter radios to bother about enforcement.

OK, pi is out, T is in.
 Now, since there doesn't seem to be any actual construction plans out there, how do I determine what the ratings of the caps and the inductor should be. How do I determine the plate spacing of the caps for high power? Will wide spaced plates for high power handling be inefficient at lower power? Should I use a roller inductor or a tapped one? Should I use a tapped inductor for coarse tuning and a roller for fine tuning? When you guys talk about Q, you lose me. I don't understand what that is at all, though it seems to be related to efficiency.
 I am not well versed in theory. I have built some projects, but they had schematics, parts lists, directions. That makes it easy. That is why I am looking for construction plans. I don't have the theoretical knowledge to design one for myself. I have built a couple of simple T tuners, they were small and easy to build with no meters, baluns, or antenna switches. I now want something that could do just about anything I could ask it to do. I'm not afraid to study a bit and learn more about what I want to do, I just don't want to spend the winter learning all that is needed to design and build. Seems there must be some folks out there who have built some mighty good tuners. I always try to use resonant antennas, but on my small lot I just can't put up six or seven different antennas.
 Although I have been licensed for 10 years, I was a novice and then a Tech for those years and didn't have to deal with HF stuff. A little bit of 10 meters was the extent of it. Now, I have upgraded to General and need to change my equipment to deal with the new bands I can use (can't wait to be called a bad name on 20 meters).
 Buying and wiring air variables and a roller inductor is relatively easy, knowing the values of these components and the plate spacing on the caps is some of what I don't know. Is there any advantage to using vacuum variable caps? Do they have the capacity needed? Are they just too costly? How do I put together a good balun that can handle high power? Right now, I don't have an amp, but that could easily change so if  put together a tuner, I want it to handle the limit.
 Is there a good book I should get that will answer my questions? That WOULD shut me up! Well, maybe for a while anyhow Maybe I should just buy a tuner? That would be like buying a foreign car though. I'd rather die.

Dale, I sure appreciate all the good info. I think a Pi tuner is what I want. Even though (as you point out) a good radio would have good harmonic suppression, I think the supressive qualities of this design would be good insurance. I also have heard that T designs can give false readings in that two very different settings will give low SWR but that only one of those two settings will give good efficiency.
 What I am looking for is construction plans. I just want to put together a good tuner that can tune just about anything and handle high power. Seems there must be a set of construction plans for such an animal out there somewhere.
 So, does anyone know of a place I might find what I am looking for?

I would like to homebrew an antenna tuner. I want to make a good one. Anyone know where to find plans for such a project? I have an AEA AT-300 but want something more substantial. I realize that I could probably buy a great one cheaper than build but I like to build and need a few projects for this winter. Is there an antenna tuner book out there?

Is there any advantage to insulating the driven element in a yagi from the boom, or is there an advantage to NOT insulating it from the boom? Any advantage to insulating the boom from the tower if the driven element is NOT insulated from the boom? Also I am going to build a 2 meter quad and wonder what effect an aluminum boom would have. If I use aluminum for the boom should I insulate it from the tower? How about using 2 reflectors for better front-back? Also, what is the unladen air speed of a sparrow?

Wolfgang, The radio is a Yaesu FT-690. I don't have the radio yet, it should arrive today. I like to build my equipment when I can. I have built cw keyers, antenna tuners, antennas, amplified microphones, nothing extravagant or overly complex. I can easily build a dipole or a yagi but wanted to hear from others about designs that work better that folks have experience with. I will just get a couple of antenna books and do some reading.

I am getting (from my brother whom I love very much) a 6 meter all mode and I need some antenna designs for homebrew. Can anyone supply some designs or direct me to some web sites where I might find some ideas?
 I am new to 6 meters and have to ask if I should go vertical or horizontal polarization. Would it be wise to do both with a switch?