should i be looking at a different wire? i can always talk to the electricians at work, they've usually got a good supply 
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attic dipole question
- Thread starter Whiplash-265
- Start date
should i be looking at a different wire? i can always talk to the electricians at work, they've usually got a good supply
ok but its 5 1/2 turns on a 4 inch diameter. if you use solid cooper wire and remove the insulation then 8 feet 7 inches should be perfect. what coax are you using?
ya, that's what i did NB 5.5 turns on 4" approx 3" off the connection, ran it as close as feasible
will try new wire....
i'm using brand new 75' stretch of RG8x
ran it thru the 259b as well before attaching and at 27.555 (which is my target freq.) i was getting a 1.4db loss, no breaks, no shorts...not the best coax, but best i can afford atm
will try new wire....
i'm using brand new 75' stretch of RG8x
ran it thru the 259b as well before attaching and at 27.555 (which is my target freq.) i was getting a 1.4db loss, no breaks, no shorts...not the best coax, but best i can afford atm
If you put a ground to earth on the antenna eliminate it and see what you get.
The dipole does not need a ground. In your attic there is no pressing need to be concerned about lightning grounding, and you can ground all your equipment for rf purposes. Do not ground the dipole. The dipole is a balanced antenna, and adding a ground in the center changes it completely. Two equal sides are the nature of the dipole, and a ground in the center will lengthen one of the sides and severely imbalance the antenna.
The dipole does not need a ground. In your attic there is no pressing need to be concerned about lightning grounding, and you can ground all your equipment for rf purposes. Do not ground the dipole. The dipole is a balanced antenna, and adding a ground in the center changes it completely. Two equal sides are the nature of the dipole, and a ground in the center will lengthen one of the sides and severely imbalance the antenna.
The biggest difference in the performance of a dipole and a vertical antenna of some kind is in polarization. A difference in polarization can make a very big difference in what you hear and where you are heard. That's normal.
The size of the wire/conductor used in making a dipole (or a vertical antenna) does have some slight affect, but nothing very significant. To make any significant differences, that difference in size has to be huge, not just several wire sizes. One good example of that is called a 'cage' dipole. That bandwidth thingy is very, very over emphasized. It's also frequency related, what may make a difference at VHF won't make any difference at HF.
There can't be any -exact- size for any particular length of resonant antenna, resonance depends on how/where the thing is mounted (among other things). How that antenna reacts to things around it. When you talk about an indoor antenna, that reacting to things around the antenna get's magnified a great deal, there's just so much stuff near the antenna. So, a little 'skootch' longer/shorter is absolutely normal. Any/all antennas can benefit from tuning. It may not be much, but there can always be some improvements in how the thing is made. There are NO "one size fit's all" antennas no matter what or who tells you there are.
One 'trick' with dipoles is that their input impedance can be manipulated by varying the angle between their 'legs'. Making that angle less than 180 degrees (a flat top) lowers the input impedance from a 'norm' of around 65 - 75 ohms to something closer to 50 ohms (same for 'drooping' the radials of a groundplane antenna!). Depending on how/where the thing is mounted, that 'droop' may not have to be very much at all. The only way I know of to tell for sure is to try it and see.
Resonance has nothing to do with input impedance of an antenna. And/or, SWR has nothing to do with resonance. One doesn't tell you anything about the other. And to complicate things just a little bit more, a resonant and properly impedance matched antenna produces a radiation pattern. If that radiation pattern doesn't put the signal where you want it to go, then that resonant and low SWR antenna isn't doing you much good, is it? That radiation pattern is a product of the antenna's length, height, and 'shape' (simple omni-directional/directional). Any and everything around an antenna affects that radiation pattern to some extent.
Ain't all this sh_ _ ... stuff just so much fun??
- 'Doc
The size of the wire/conductor used in making a dipole (or a vertical antenna) does have some slight affect, but nothing very significant. To make any significant differences, that difference in size has to be huge, not just several wire sizes. One good example of that is called a 'cage' dipole. That bandwidth thingy is very, very over emphasized. It's also frequency related, what may make a difference at VHF won't make any difference at HF.
There can't be any -exact- size for any particular length of resonant antenna, resonance depends on how/where the thing is mounted (among other things). How that antenna reacts to things around it. When you talk about an indoor antenna, that reacting to things around the antenna get's magnified a great deal, there's just so much stuff near the antenna. So, a little 'skootch' longer/shorter is absolutely normal. Any/all antennas can benefit from tuning. It may not be much, but there can always be some improvements in how the thing is made. There are NO "one size fit's all" antennas no matter what or who tells you there are.
One 'trick' with dipoles is that their input impedance can be manipulated by varying the angle between their 'legs'. Making that angle less than 180 degrees (a flat top) lowers the input impedance from a 'norm' of around 65 - 75 ohms to something closer to 50 ohms (same for 'drooping' the radials of a groundplane antenna!). Depending on how/where the thing is mounted, that 'droop' may not have to be very much at all. The only way I know of to tell for sure is to try it and see.
Resonance has nothing to do with input impedance of an antenna. And/or, SWR has nothing to do with resonance. One doesn't tell you anything about the other. And to complicate things just a little bit more, a resonant and properly impedance matched antenna produces a radiation pattern. If that radiation pattern doesn't put the signal where you want it to go, then that resonant and low SWR antenna isn't doing you much good, is it? That radiation pattern is a product of the antenna's length, height, and 'shape' (simple omni-directional/directional). Any and everything around an antenna affects that radiation pattern to some extent.
Ain't all this sh_ _ ... stuff just so much fun??
- 'Doc
Ya 'Doc. I haven't had this much fun since.....Well I do know my back is killing me this morning lol
It is a flat top presently and i can get a r=50 it the 11 meter but the X is up in the 100+ something definitely wrong there. AT 54mhz i'm seeing a nice 50/9
Today Im gonna rip 'er all down and go over it all again, and maybe try relocating to another section of the attic with less wiring..it's not like i don't have enough coax for it Time to hit up the home depot and try improving on my list of tuning parts available
HomerBB. No ground installed.
greatly appreciate the help all!!!
It is a flat top presently and i can get a r=50 it the 11 meter but the X is up in the 100+ something definitely wrong there. AT 54mhz i'm seeing a nice 50/9
Today Im gonna rip 'er all down and go over it all again, and maybe try relocating to another section of the attic with less wiring..it's not like i don't have enough coax for it
Time to hit up the home depot and try improving on my list of tuning parts availableHomerBB. No ground installed.
greatly appreciate the help all!!!
Glad you are having fun with building the antenna. the hobby is all about fun.
Maybe build the antenna outside away from any wires etc etc in the backyard if you have the space.
Once you know your antenna is resonant outside, then move it inside and try it with a "known good antenna" that worked outside.
Then hopefully you just need to touch up the antenna when it is installed in the attic.
Maybe build the antenna outside away from any wires etc etc in the backyard if you have the space.
Once you know your antenna is resonant outside, then move it inside and try it with a "known good antenna" that worked outside.
Then hopefully you just need to touch up the antenna when it is installed in the attic.
k, got it between 2 trees in the back yard and finally have something to start with i think
weird tho, i've had to cut each side of the dipole below 8' to even get close to a match @ 27.555
i'll get her back up in the attic and see what happens..if it's a total kibosh i'll just try new wires and start again
thanx again guys!!
weird tho, i've had to cut each side of the dipole below 8' to even get close to a match @ 27.555
i'll get her back up in the attic and see what happens..if it's a total kibosh i'll just try new wires and start again
thanx again guys!!
and back in the real world where i'm 25 feet above ground in the attic...
i'm great if i get my ham license
what i've done differently from the early wire version is removed the plexiglas plate and the bolts from the build...all i have now is coax running straight to the wires. Wonder if the bolts were throwing everything outta wack
will get new wire tomorrow
i'm great if i get my ham license
what i've done differently from the early wire version is removed the plexiglas plate and the bolts from the build...all i have now is coax running straight to the wires. Wonder if the bolts were throwing everything outta wack
will get new wire tomorrow
ok 8 feet 7 inches is wrong for 555. it should be8 feet 6 inches if its solid without insulatoin. if your using like 92% velosity facter wire thats insulated and stranded then it should be about 7 feet 9 1/2 inches
If that plexiglas and bolts were the center insulator, then they have no appreciable effect on the antenna. Making it that way just makes the whole thing easier to deal with, put together. If not using that center insulator but only the coax, then there's a chance that the strain will pull that coax apart a little. Not a biggy, but keep it in mind if you see significant changes.
If the antenna worked outside, then hang it in the attic and try it there. I'm sure the SWR will change, but that can be compensated for easily, just 'droop' the legs of that dipole a bit (that dipole doesn't have to be perfectly straight). Leave the length of the thing alone. If the 'X' was as low as you can get it, it's resonant, which you want.
- 'Doc
If the antenna worked outside, then hang it in the attic and try it there. I'm sure the SWR will change, but that can be compensated for easily, just 'droop' the legs of that dipole a bit (that dipole doesn't have to be perfectly straight). Leave the length of the thing alone. If the 'X' was as low as you can get it, it's resonant, which you want.
- 'Doc
Glad to see you got it going.
I use PVC pipe for cneter pieces and insulators.
It is cheap and one 10' stick sure can make a lot of antennas.
The wire measurements are all to get you in the ball park per say.
Resonance depends on so many variable factors. Height above ground, type of ground. Angle of each dipole leg. Anything in the area within a couple of wave lengths that can effect the antenna. structures and on and on. there is no "Perfect" formula to build a wire antenna and make it work every time.
As you are finding out.
I use PVC pipe for cneter pieces and insulators.
It is cheap and one 10' stick sure can make a lot of antennas.
The wire measurements are all to get you in the ball park per say.
Resonance depends on so many variable factors. Height above ground, type of ground. Angle of each dipole leg. Anything in the area within a couple of wave lengths that can effect the antenna. structures and on and on. there is no "Perfect" formula to build a wire antenna and make it work every time.
As you are finding out.
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