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ctech4285
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two antennas with a spillter?

Tue Sep 14, 2010 5:29 am

would it be possible to gain 3dbi if you connect two directional antennas together for a link? is there anything to watch out for?
 
RK
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Re: two antennas with a spillter?

Tue Sep 14, 2010 8:27 am

Did you forget that you lose 3 dB when you split the signal?
-3 dB + 3dB - time - material - lossy connectors = you lose
 
ctech4285
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Re: two antennas with a spillter?

Tue Sep 14, 2010 9:05 pm

but the recieve gain is +3dbi minus some losses. and since an antenna works as sender and reciver equal it has to give a gain sending unless my premis is wrong. the beem width has to decrease i think.

there is an error in you logig
 
FIPTech
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Re: two antennas with a spillter?

Wed Sep 15, 2010 12:01 am

Should works. This is done almost every time on GSM towers, with 3 or 4 sectorial antennas and a coupler. The goal is more to get the exact field coverage you need than getting more gain.

Nevertheless it's not a job for beginners. You'll need to verify at least the ROS (stationnary waves) so that you got a performance increase and not a decrease.

At those frequencies, ROS meters and spectral analysers are not cheap... But if you can buy or rent them, and accept the learning curve, why not...
 
ctech4285
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Re: two antennas with a spillter?

Wed Sep 15, 2010 5:46 am

are you talking about the return reflection on an antenna causing a standing wave in the coax cable that propagates back out of the antennas, and if theirs resonance this signal will grow endlessly? could you not connect a second radio card via splitter (or better yet just point an antenna right at the cable so you don't get +60dbm on the input of your card and run a spectral scan too see if and at what f you have standing wave? they would have to be the same frequency as your sending right?, just maybe out of phase with your primary signal?

the interference pattern should be simple enough if you keep the design simple. so antennas center distance at lambda x, antennas in line with each other and the coax cable the same length you should be fine, i think

for a link i am considering doing, at one location the spectrum is all dirty and used up.
but if you where to place the two antennas (or maybe 3) at something like 20 meters apart you could make your first destructive interface 34m wide at a distance of 115km. meaning you would not see anything +-34meters from your tower. i am not sure how much weaker the second constructive interference would be in this case 70m from center at 115km (these numbers should be withing +- factor 2)
 
ctech4285
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Re: two antennas with a spillter?

Wed Sep 15, 2010 6:09 am

oh one more thing, will the impedance change if you connect two antennas together??
 
FIPTech
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Re: two antennas with a spillter?

Wed Sep 15, 2010 9:43 am

Again you should not do this wihout serious testing tools. SWR meter and spectral analyser, or there are good chances you will end with a lower quality link, because of impedance matching problems, or interferences between antennas.
 
BlackDragon
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Re: two antennas with a spillter?

Sat Sep 25, 2010 1:53 pm

There are special splitters that are used for this and to get around the losses there are amps too, but there is no free ride.
You must make sure that you use proper site design and good quality coax i.e. LMR400 with N end connectors.
 
ctech4285
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Re: two antennas with a spillter?

Sat Sep 25, 2010 11:47 pm

is there any reading material/books on this specific topic? i would like to do a link some times
 
FIPTech
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Re: two antennas with a spillter?

Sun Sep 26, 2010 1:29 pm

If you are interested by advanced antenna setups, i advice you to enter the Ham radio world (amator radio) through Internet searches and forums.

There are lots of readings available, software tools, schematics, books on the subject and a lot of friendly guys with very advanced knowledges.

Antenna setup for wifi is not very different than general radio rules, and hardware for setting up antennas is not different as well. You will find in the Ham world all the tools you need. Most of the time free (for softwares), sometimes very cheap for test hardware (for the one you can do yourself), sometimes very expensive like professional spectral analyzer and swr meters.


If you are not ready to spend a lot of time to learn radio technics and experiment, or you can't buy basic test hardware, i advice you to keep things simple and buy ready made antennas / wifi hardware.

Radio is not something simple, it's more like an art.
 
BlackDragon
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Re: two antennas with a spillter?

Sun Sep 26, 2010 1:57 pm

If you are interested by advanced antenna setups, i advice you to enter the Ham radio world (amator radio) through Internet searches and forums.
:shock: You beat me to the punch line :)

I would suggest to look around your town to find an amateur radio club you will most likely find some well weathered antenna experts maybe an actual cell site technician that can point you in the right direction.

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