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11meter dipole
- Thread starter bigred222
- Start date
haha thanks c2 whats up man. uhh i was gonna run it for base use on a count of i have a mammoth yard and my antron is blocked from the east side of my house, so when skip runs hard over the Atlantic lets just say i want to be well prepared. haha
73's all
73's all
I'll do you one better:
http://www.radiowavz.com/html/c_b____11_meter.htm
I have one of these and will continue to play with it. So far, I'm impressed with this Double Bazooka! You can't beat the price!
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A simple dipole is easy to make. Its better if you use some sort of choke balun at the feedpoint, but not necessary.
http://www.radiowavz.com/html/c_b____11_meter.htm
I have one of these and will continue to play with it. So far, I'm impressed with this Double Bazooka! You can't beat the price!
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A simple dipole is easy to make. Its better if you use some sort of choke balun at the feedpoint, but not necessary.
I can do dat!
Decide what frequency you want the thing resonant on. divide that number into 468 and you come up with the length of a 1/2 wave dipole (close, but not exact). Add about a foot and a half of wire to use in making the center connections and for twisting back on it's self at the ends. There's the wire, now for a center insulator and connection point for the coax.
You have a choice, buy one or make one. If you want to make one you'll need a piece of plastic/plexiglas about 2" by 4" by something like 1/4 to 1/2" for thickness (bigger won't hurt). Drill one hole close to each end to connect the wires to, and get real fancy and put a 1" hole in the center to mount an SO-239 connector. Mount SO-239 in center insulator, connect one wire (some of that 'extra' part you added) through that hole near one end which will support the wire, to the center pin of that SO-239. Same with the other side except connect to one of the bolts holding that SO-239 to the center insulator. Haul the whole thing up into the air and test for SWR. Trim the wires equally on each side till you get the lowest SWR, then quit trimming. Don't cut any wire off of the ends, just twist it back onto it's self. That's a simple dipole.
For a 'Bazooka' type doublet there's only one other thing you need to know. The velocity factor of the coax used. I'd suggest using a 'solid' dielectric coax, and since it's going to be fairly heavy, why not RG-58u? Why the velocity factor? Cuz that's gonna determine how far from the center that you will short eacj 'leg' of the doublet. Each leg of a bazooka, from center point to where it's shorted is an electrical 1/4 wave length long. So, 246 x VF = feet of coax from center point to short. The rest of the length of that leg can be found in one of two ways. Just cut it like you would for a regular dipole (234/f(in Mhz)) - the 1/4 wave length section. Or, go to the trouble of determining the 'k' of the coax (diameter) which will give you the total length, then figure total length minus the center 1/4 wave section, and you got the length for half of the bazooka. Sounds a lot harder than it really is.
To condense it;
Regular wire dipole length = 468/f(in Mhz), then trim to resonance/low SWR.
For a bazooka, each center section of coax = 246 x VF. Each end section of each leg is about the length needed to make each half of the bazooka half of 468 / f(in Mhz). That will give a length just a bit too long, which is much easier to deal with that a length a bit too short. [If I remember correctly, the 'magic' number for a bazooka is '460' instead of '468' for total length. The extra '8' is just for a 'fudge factor' and at 27 Mhz just isn't gonna be much at all.]
If you can't do that and come out under $35, you just ain't trying too hard.
- 'Doc
Oh. At the center point of that bazooka, the only thing that's 'cut' is the braid, NOT the center conductor. The braid from one side is connected to the braid of the coax feed line. The braid from the other side of the bazooka is connected to the center conductor of the coax feed line. There are some variations on that, but that's the simple way of doing it. Power limits. I never had any problems feeding an RG-58u bazooka with legal limits (about 1500 watts). If you're gonna be using more power than that I'd go to RG-8u instead of RG-58u. No idea what that will handle. If you're gonna be using anything close to 10K watts, you're an idiot.
Decide what frequency you want the thing resonant on. divide that number into 468 and you come up with the length of a 1/2 wave dipole (close, but not exact). Add about a foot and a half of wire to use in making the center connections and for twisting back on it's self at the ends. There's the wire, now for a center insulator and connection point for the coax.
You have a choice, buy one or make one. If you want to make one you'll need a piece of plastic/plexiglas about 2" by 4" by something like 1/4 to 1/2" for thickness (bigger won't hurt). Drill one hole close to each end to connect the wires to, and get real fancy and put a 1" hole in the center to mount an SO-239 connector. Mount SO-239 in center insulator, connect one wire (some of that 'extra' part you added) through that hole near one end which will support the wire, to the center pin of that SO-239. Same with the other side except connect to one of the bolts holding that SO-239 to the center insulator. Haul the whole thing up into the air and test for SWR. Trim the wires equally on each side till you get the lowest SWR, then quit trimming. Don't cut any wire off of the ends, just twist it back onto it's self. That's a simple dipole.
For a 'Bazooka' type doublet there's only one other thing you need to know. The velocity factor of the coax used. I'd suggest using a 'solid' dielectric coax, and since it's going to be fairly heavy, why not RG-58u? Why the velocity factor? Cuz that's gonna determine how far from the center that you will short eacj 'leg' of the doublet. Each leg of a bazooka, from center point to where it's shorted is an electrical 1/4 wave length long. So, 246 x VF = feet of coax from center point to short. The rest of the length of that leg can be found in one of two ways. Just cut it like you would for a regular dipole (234/f(in Mhz)) - the 1/4 wave length section. Or, go to the trouble of determining the 'k' of the coax (diameter) which will give you the total length, then figure total length minus the center 1/4 wave section, and you got the length for half of the bazooka. Sounds a lot harder than it really is.
To condense it;
Regular wire dipole length = 468/f(in Mhz), then trim to resonance/low SWR.
For a bazooka, each center section of coax = 246 x VF. Each end section of each leg is about the length needed to make each half of the bazooka half of 468 / f(in Mhz). That will give a length just a bit too long, which is much easier to deal with that a length a bit too short. [If I remember correctly, the 'magic' number for a bazooka is '460' instead of '468' for total length. The extra '8' is just for a 'fudge factor' and at 27 Mhz just isn't gonna be much at all.]
If you can't do that and come out under $35, you just ain't trying too hard.
- 'Doc
Oh. At the center point of that bazooka, the only thing that's 'cut' is the braid, NOT the center conductor. The braid from one side is connected to the braid of the coax feed line. The braid from the other side of the bazooka is connected to the center conductor of the coax feed line. There are some variations on that, but that's the simple way of doing it. Power limits. I never had any problems feeding an RG-58u bazooka with legal limits (about 1500 watts). If you're gonna be using more power than that I'd go to RG-8u instead of RG-58u. No idea what that will handle. If you're gonna be using anything close to 10K watts, you're an idiot.
linearone,
I'm assuming you are talking about the 'bazooka', and...
Does it really tune to 1:1? Just depends on how well you tune the thing, how high it is, what's around it, and how 'lazy' your SWR meter is. Can it? Yes, Will it? Maybe. And will it stay 1:1 over a wide range of frequencies? ... Now, that's a 'trick' question, and it has a fairly un-tricky answer. The simple answer is that an SWR meter will show an 'almost' 1:1, or whatever the lowest SWR obtained was, over a kind'a wide frequency range, certainly the 40 channels of CB. What that simple answer doesn't say is that the further from the design frequency you are, the less the antenna's efficiency is due to the reactances present in those two "1/4 wave matching stubs" used to feed the thing (reactances do not radiate). Further from design frequency, higher the reactances, and lower the radiation efficiency. [Keep that in mind when you see those 'super wide' band antennas.]
- 'Doc
I'm assuming you are talking about the 'bazooka', and...
Does it really tune to 1:1? Just depends on how well you tune the thing, how high it is, what's around it, and how 'lazy' your SWR meter is. Can it? Yes, Will it? Maybe. And will it stay 1:1 over a wide range of frequencies? ... Now, that's a 'trick' question, and it has a fairly un-tricky answer. The simple answer is that an SWR meter will show an 'almost' 1:1, or whatever the lowest SWR obtained was, over a kind'a wide frequency range, certainly the 40 channels of CB. What that simple answer doesn't say is that the further from the design frequency you are, the less the antenna's efficiency is due to the reactances present in those two "1/4 wave matching stubs" used to feed the thing (reactances do not radiate). Further from design frequency, higher the reactances, and lower the radiation efficiency. [Keep that in mind when you see those 'super wide' band antennas.]
- 'Doc
Those bazookas tune real nice and are real broad banded. I have hit tons of skip with one of those radiowavs bazookas.