Homebuilt 10-12 meter antenna

[Cruiseomatic]

I want to build a antenna that covers 10, 11, and 12 meters and not need 3 different antennas. This is for both TX and RX. I'm building it out of PVC and 10 AWG wire. I would like it to be 5/8 wave vertical. I have some physical designs in mind. Like this one: Ш
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3 elements sharing a common ground. How far apart should they be? How long should my ground wire be? Can this even be done? What else will I need to pull this off?

Thanks.

 

[LtDoc]

It can be done, and is quite often with 1/4 wave antennas. The further apart the bands are the easier it will be though. All of the elements are going to interact, affect each other, so tuning is going to be real fun. You will need an impedance matching device for a 5/8 wave antenna, the same device may not work for all three bands, no experience with that one.
Good luck!
- 'Doc

 

[Cruiseomatic]

I'm going with 5/8 for a low angle of radiation towards horizon. The diagram didn't show up like I wanted to. It is basically a "E" on its back sitting on a stick in the middle. What type of matching device would work? If I would need one though, Couldn't I shoot for .64 wave? I know with a multi-band antenna I will have efficiency issues.

 

[LtDoc]

First, the 5/8 (.625) vs .64th wave antenna length thingy. That's a myth, there's no practical difference in performance between the two. But if you want a .64 wave antenna you can certainly make the length that, or any other percentage you'd like.
Probably the most common impedance matching device with a 5/8 wave vertical antenna is a tapped coil between 'whip' and ground. (That small coil at the base of a 5/8w vertical.) What size is that coil, the height/width, number of coil turns above that tap point and below it? I can't tell you, there are too many variables for me to guess about. It amounts to the right amount of reactance between 'whip' and tap point and between the tap point and ground. Since the length of that whip also adds reactance into it, the turns count/ratio isn't 'fixed' or 'set', it can change. That's one reason why that '5/8'/'.64' thingy isn't a fact. You can make the coil turns above the feed point slightly less and the whip longer to still get a 50 ohm input impedance. Do that 'juggling' correctly and the whip can be almost any length you care to make it, sort of.
Have fun.
- 'Doc

 

[WA0CBW]

And to add to what LtDoc said if you want it to do 3 bands then you will have to have 3 different length whips and 3 different coils or one whip and 3 different tap points on the coil depending on which band you are using. Not very user friendly. Rule of thumb says a multi-band antenna is a compromise and can be equally poor on all bands.

BB

 

[Cruiseomatic]

If there is no real difference, I'll stick with 5/8 wave. What size PVC should I use though? I was thinking 1" maybe 3/4". Nothing to big. So far to calculate needed wire length for 11 meters, I have Length = 585/27.205 Which is about 21.5 feet. Still working on 10 and 12.

 

[LtDoc]

Trying to stand 22 - 23 feet of PVC up in the air is really going to be a challenge. I wouldn't even try it with PVC. I think I'd use chain-link fence top rail, two section of it and tack/bolt/weld a 2 or 3 foot stiff wire on the top end to make up the right length (close enough anyway). At that length you probably wouldn't need to guy the thing. Doing the mounting at the bottom is fairly uncomplicated. Bolt the thing to a wooden post/2x4/4x4/whatever. Put that coil at the bottom end and run the ground radials. It doesn't have to be 'sophisticated', plain and simple works just as well.
- 'Doc

(Put a nice small bird house at the top. Tell the neighbors it's for migratory humming birds.)

 

[Cruiseomatic]

Haha, I'm going to coil the wire around the PVC pipe. 22 ft. of PVC is way to long to even think about. Do I have the correct numbers for 11 meters though? What is the formula for 10 and 12? I decided to keep all the elements separate and just run 3 coaxs to it but keep a common ground. How close can I wrap this wire together though?

 

[mtindor]

Is it not possible for you to get a simple trapped dipole up about 32-36 feet?

1. A dipole is bidirectional, with all of the gain broadside to the dipole. There are nulls, in some cases heavy nulls. So unless you have a specific place you want to point it stationary, or unless you have a rotator [mechanical or armstrong], this might not be a solution.

2. A dipole is going to have significantly more gain than any vertical you are likely to build IF you can get it up at least a half wavelength. At a half wavelength height (16-18 feet), it'll do pretty good on DX, but it won't be a long haul performer. Get it up to a wavelength (32-36 feet), and it'll beat a vertical any day, by a large margin, for signals broadside to the dipole.

You could make a trap/coil to give you 10m / 12m. That won't get you 11m, but if you've got 10m and 12m [at least at the peak of the cycle] you'll have plenty to work without dealing with 11m.

Of course, you could always use an antenna tuner [which will likely give you a little loss] to tune 11m if that's a must for you.

Anyway, if you can stick something the size of two fishing poles separated by a T, horizontal, at 32-36 feet, you'd be having a helluva lot of fun chasing DX. And you don't need anything thick. Build one out of fishing rods. Or get some nice small fiberglass tubing [ http://www.mgs4u.com ].

If you can't put a dipole up at any height, then forget what I said. Remember though, a 10/12m dipole is going to be extremely light and isn't going to create any kind of appreciable windload on whatever kind of mast you stick it on.

mike

PS: My gain claims are vs a 1/4w vertical. You're talking about a 5/8w dipole, and I'm not sure about gain figures. But I'm fairly certain that no matter how you slice it, if you can get the height and can deal with the bidirectional nature of the dipole, it'll be a better performer than the vertical -- and will not be quite the eyesore that a multielement vertical may be [if you have neighbors who are pains in the ***].

 

[LtDoc]

I'm afraid that winding wire around that PVC isn't going to produce a usable 5/8 wave antenna. By shortening that 22 - 23 feet of antenna into something less than that, you don't have a 5/8 wave antenna anymore. It won't have the same characteristics (radiation pattern) as a 5/8 wave antenna no matter how much wire you use to make it. An antenna's physical length determines it's 'size'.
I'm sure you could make an antenna such as you're thinking of work. But you won't have a 5/8 wave antenna, nor it's benefits (gain).
Adding other windings on the same PVC pipe for two other bands isn't going to yield a very easy to make -working- antenna, it'll be a real PITA to tune. Especially with those antennas being so close to each other, they will affect each other.
Good luck.
- 'Doc

 

[jhooten]

Or you could put up a 10 foot antenna and autotuner either at the base or the radio and call it good.

 

[Cruiseomatic]

Dipole is not practical right now. No where to hang it or set it up. Anything I do will have to be self supporting and go up. I suppose I'll stick with an 11 meter for now since it is somewhat busier here. I couldn't coil the wire at the bottom or wherever and then run a straight line like a loaded antenna does or keep the elements 8 ft. apart? I realize that I could just buy all three cheaper than make this one but thats the fun in this. If this would be so hard for just 3 different meters close together, How do these commercial mfrs. pull it off so well? I've seen some that (And I don't fully believe this...) cover from 10 all the way to 80 or 160m?
Is there anyway I can build it for 11 meters and use thick enough wire or tubing to have more bandwidth so I won't need a tuner as much? I remember my Imax would cover half of 10, all of 11 and half of 12. But it is still in Houston and I'm in the desert right now.

Thanks for the help guys.

 

[acyddrop]

You can build a multi-band non-resonant antenna for not a lot of money. You'll need modest (and I truly mean modest) soldiering skills, a drill and bits, and about $100 (probably LOTS less).

UnUn design
This is where the modest soldiering skills come in. To create an unun for modest power (300 watts or less) you can obtain about 10 feet of wire, an FT-240-61 ferrite toroid for the core, some 3M electrical tape, a soldiering iron, some soldier, and a handful of parts (bolts, nuts, washers and waterproof box) from home depot. If you're going to be handling more than 300 watts you'll want to change the wire from 600v insulated stranded wire to PTFE insulated stranded wire. In both cases 18ga wire will be enough for this project, though you can use 16ga or 14ga if you can find that more easily. You'll also want some ring terminals, though these are options. I use ring terminals that go around a 1/4-20 bolt and hold 18-16 ga wire. I buy my cores from Alltronics surplus but you can go right to Amidon for them too.

You'll want to two wires (so parallel speaker wire for low wattage works here) but you can also have 2 separate wires and loosely wind them around each other to create a bifilar winding. Next wrap those wire pairs around the FT-240-61 core 12 - 15 times (I get good results with 12 turns either in parallel or bifilar). You'll need to soldier connections together. If you do this just private message me for a wiring diagram, or look on the internet).

Antenna
For the aluminum sections you can get those from DXEngineering. Depending on the total height you want you'll need to buy the appropriate number of 6ft sections. I suggest you make the lowest section from their thicker aluminum which is the 0.120in walled stuff. Make this section your short section (3ft) because this stuff is more expensive than the rest of the aluminum. Just know that doing this will require you by the next larger size up from what you think. In other words, if you got a 1.750" OD 0.120in tube you'll need to buy the 1.500" OD 0.058in tube and not the 1.650" as you would expect to with the thinner stuff. After that just buy your aluminum the next size down. 1.500" to 1.375" and so forth up to the desired height (I figured for 21') one 3 ft section and three 6 ft sections.

This setup WILL require a tuner to use properly, it'll also need either a modest ground plain or a counterpoise. If you're strapped for room, buy yourself some galvanized metal mesh (also at Home Depot or Lowes) and lay that out in place of lots of ground wires.

Hope this helps...