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hgb
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increase recieve sensitivity

Sat Dec 30, 2006 8:30 pm

hi to all ,

we have a WISP now and we need to perform a laptops service for our costumers , and we want to make the connection available for roaming users , from the street , malls and from many areas .

we have now SR2 with RB/532 and 15dbi omin for each station .

the sensitivity is good for our clients with a 12dbi patch antenna and SR2 or cb3 radio , but we need to deploy the laptop solution to enable the laptops to connect directly to our base stations .

we will deploy also an SR2 or NMP-8602(26dbm) mini-pci for the laptop users , or they may will use there based wireless card built in the laptops which is 35mw :S (mostly will deploy SR2)

now i can increase the base station Signal power by using an AMP for say 1 watt or 2 watt , and the laptop romaing clients in the city :) can listen and find the ssid with a good -db level say -70 . but i cant connect ofcourse from far places but i can now from inside bulding near to the street and after that no any buildings in the way with the BS ,,,, i dont have any problem in the speed the minimmum speed is good , even 5kb/s , just somthing that made the connection happened .

my question is how to increase the recieve sensitivity level in my Station the SR2 -db level limit is -98(+/-)2 , but i need more !! any ideas to increase this for say -106db ? bigger antenna ? an ampilifier to increase recieve gain ? filters ? recieve divirsity using 3 omini directional antenna with 120 dgree ?

what is the best to perform , and thanks in advance .
 
hgb
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Sun Dec 31, 2006 10:57 am

Do the AMP will increase recieve gain really ? that i have an AMP with 20 db recieve gain , is that mean the recieve sensitivity now is = -98(for the SR2) -20 = -118 db ?

or just it is a bla bla info ?

thanks ..
 
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tneumann
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Sun Dec 31, 2006 2:34 pm

I think you are going the wrong way about this. The obvious idea of combining an amplifier with an omni antenna usually does not work very well. The reason is that tx-power and rx-resitivity are one thing (the amp does help with those, at least if all you do is look at the numbers) but the other, at least equally important thing is signal-to-noise ratio (SNR). An amp does also amplify the noise, often radically so, and therefore it does not help you to get better SNR. And if you're using omni antennas this is also bad for SNR because an omni does feed 360 degree of noise into one radio. Another point regarding the antenna: If you really plan to use a 15 db omni as an AP for laptop users you should be aware that an omni with such a high gain (15 db is quite a lot for an omni) has a very narrow vertical RF pattern, so your laptop users would mostly need to be on the same height as the antenna.

I think you shoud cover the area with more APs, preferrably using sector antennas (3 x 120) with one radio per antenna, using omnis only in small, contained areas such as convention center halls, sports arenas etc. Aim for a consistens SNR of at least 20 db for your laptop users and you will have good connection quality.

--Tom
 
hgb
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Thu Jan 04, 2007 11:12 am

tx-power and rx-resitivity are one thing
ok this is something i need to understand , i knew that if i received a low signal in mi 15 dbi omni and the AMP is connected to the omni , then this low signal will be amplified too with the amplifier , then it will make the signal clearer for the radio which is connected with the AMP , is that true ?

Also i have AMP with a low noise 5db noise (as they said in the manual) ,,

i want also to use the amp with 1 Watt with 1 WATT with the omni because the Omni will spread the signal in 360 dgree , and the signal for the bridge users with 12 dbi patch ant , will not be enough if we assume the normal connection between 2 SR2 radios with 2 12dbi patch directional in each side happened correctly .

the 15 dbi is not a good thing as you said because the vertical pattern , i will try 3 14dbi sectorized omni instead .

finally is any one try an idea like this before ? installing SR2 instead of the built-in mini-pci card in the laptops ?(it will EAT the battery offcourse :P )
also acer laptops has a technology named "Signal up" which is used to make a good signals in send an receive ( i test it and its great by the observation compared by many laptops and usb adapters that iv used , and i didnt take the numbers in that time )

my idea is using acer with SR2 ,,,
the SNR now with the SR2 and RB532 is -98 ,,

is there any chance to make this for reality ? be aware that i need to throw with this signal into one or 2 buildings for each user .
 
hgb
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Thu Jan 04, 2007 11:25 am

also acer laptops has a technology named "Signal up" which is used to make a good signals in send an receive ( i test it and its great by the observation compared by many laptops and usb adapters that iv used , and i didnt take the numbers in that time )
Siganl up technology :
http://www.acer.com.ph/signalup.php
 
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tneumann
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Thu Jan 04, 2007 7:37 pm

i knew that if i received a low signal in mi 15 dbi omni and the AMP is connected to the omni , then this low signal will be amplified too with the amplifier , then it will make the signal clearer for the radio which is connected with the AMP , is that true ?
Not, not clearer, just louder. Assume that you are trying to listen to some music on your stereo, but in the next room some construction workers are using heavy tools that make so much noise that they are almost as loud as the music from your stereo. You will not be able to hear the music clearly, because the difference between the volume of the noise and the music does not allow you to differentiate the music clearly from the noise. It's the difference in volume that makes the music distinguishable from the noise. If both the music and the noise were to gain the same amount in volume the mix of music and noise would just be a lot louder overall, but you will still not be able to better differentiate the music from the noise despite the fact that the db value of the music has increased. That is what your AMP does: it makes the music and the noise louder, and both equally so. The relative difference between them (SNR - signal to noise ratio) remains the same.

--Tom
 
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nickb
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Fri Jan 05, 2007 6:28 pm

I've been WISPing for 7 years now. Way back in the day when a "high power" radio was 17dBm you pretty much had to use amps - and it wasn't too bad, because the ambient noise levels were low.

In todays environment there is a HUGE amount of raw noise out there (2.4Ghz phones, and the hundreds of in-home AP's in towns). Amplifiers are almost always a very bad idea!

In SOME situations they can be useful, but I have been very successful on 5 seperate sites replacing 1W amplifiers with SR2 cards, and receiving BETTER performance! The signal levels "read" lower in the registration table, but the clients work better, I can get more on, and I can get them on farther away!

Our context, for refrence, is a rural setting. We generally put our AP's on top of grain elevators and the like, with a maximum client range ~15 miles with SR2 and about ~8 miles with CB3/EZ3+, though some special cases have been as many as 18 miles on a CB3.

So, if I'm saying anything here, it's "Don't use amplifiers".

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