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Antenna placement

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FPR1981

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You will need to cut it down. I didnt notice it's a full wave. 34 feet long.
 

FPR1981

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A half wave dipole is only about 16 feet. That's what you want. I didnt notice the first was full wave.
 
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Take 18 feet of solid core wire.
Cut 2 links at about 8.4 feet.
Soldier a lenght of coax in the center.
Take the two ends a install glass or plastic insulators.
Tie them about 45'
Tie the center on some PVC pipe.
Take the coax to your transmitter.
Wow.
Maybe 2 or 3 dollars for the ant.
Plus coax and PVC.
I did this for my old CB days and worked great.
It has no gain, but works for low dollars.

DW
So.cal
 

rcraig114

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OK, no worries. I'll cut down both sides so the total length is 16'.

Robert
 

FPR1981

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OK, no worries. I'll cut down both sides so the total length is 16'.

Robert

Start by making it 8.5 feet per side, check SWR and do further trimming of equal lengths from there.

Better to start with too much than too little.

And a dipole should be 2.15db gain. They talk great.
 

rcraig114

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Can I test and trim while on ground level? I don't know about your attic, but going up and down 4 times to trim a bit of wire is near impossible with all the climbing I have to do.

Robert
 

FPR1981

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Can I test and trim while on ground level? I don't know about your attic, but going up and down 4 times to trim a bit of wire is near impossible with all the climbing I have to do.

Robert
Yes. I would string it up outside at like clothesline height and check it with a shorter length of coax.
 

WB9YBM

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I guess I'm a bit confused here. Why can't this antenna be used in this application?

A mobile antenna is typically designed to operate on top of a ground plane the general size & shape of a car. It's also designed to resonate at a shorter over-all physical length so it doesn't bang into low bridges, garage doors, & etc. Meanwhile, a base station antenna has a ground plane designed to take the place of a car body. Also the over-all physical length is closer to an electrical 1/4-, or 1/2-wavelength (since we're not worried about hitting a bridge from a mobile) which will also give better on-air performance.
 

WB9YBM

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Can I test and trim while on ground level? I don't know about your attic, but going up and down 4 times to trim a bit of wire is near impossible with all the climbing I have to do.

Robert

I've read in a few references that if an antenna is less than a 1/2 wavelength (some say full wavelength) above ground, the impedances will be off (although it might still be on frequency)...
 

prcguy

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That's a very broad statement. A horizontal dipole at 1/2 wavelength or multiples will be closer to free space impedance and when it gets to 1/4 wave or lower above ground the impedance can go quite low. But its different for a vertical antenna and their impedance is not skewed as much by height. Their radiation pattern is and 1/2 wavelength multiples above ground are best for low angle near the horizon.

I've read in a few references that if an antenna is less than a 1/2 wavelength (some say full wavelength) above ground, the impedances will be off (although it might still be on frequency)...
 

prcguy

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Unity gain is a fuzzy term unlike dBd referenced to a 1/2 wave dipole and dBi referenced to an isotropic radiator. From antenna mfrs I'm familiar with who use unity gain figures, I believe its a comparison to a 1/4 wave ground plane in most cases, which is slightly less gain than a 1/2 wave dipole by a dB or so.

Maybe my error, but I thought a wire dipole was a unity gain.
No?

DW
So. Cal
 

rcraig114

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I am working on a dipole as we speak, along with building a bigger ground plane for the one I have on the roof. In the mean time, I'm looking at some base station antennas on the market with varying prices. I'm noticing most of these are 18 feet and taller. Question though, should the mount for these big antennas be at the peak of my roof or can I mount it half way down the chimney or something so as to not be as tall? I ask because we get some pretty hefty winds around here (hurricane state) and 18' above my roof line would probably make this antenna a flying dart.

A few I'm looking at (have to get permission from the Mrs. for these big guys)





Robert
 

FPR1981

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I am working on a dipole as we speak, along with building a bigger ground plane for the one I have on the roof. In the mean time, I'm looking at some base station antennas on the market with varying prices. I'm noticing most of these are 18 feet and taller. Question though, should the mount for these big antennas be at the peak of my roof or can I mount it half way down the chimney or something so as to not be as tall? I ask because we get some pretty hefty winds around here (hurricane state) and 18' above my roof line would probably make this antenna a flying dart.

A few I'm looking at (have to get permission from the Mrs. for these big guys)





Robert

Having owned the A99 and the IMAX, I would tell you that they're decent, but overpriced compared to the Sirio 27 aluminum ground plane. I spent $95 shipped for mine, and it will eat an A99 for breakfast. It's super lightweight too, and easy as hell to tune.
 

rcraig114

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OK, how much of this thing needs to be exposed above the roofline?

Robert
 
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